Guidance

Operational guidance for investigating and managing STI outbreaks

Updated 4 June 2024

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Introduction

A key function of the UK Health Security Agency (UKHSA) is to protect people from outbreaks of infectious disease. UKHSA operational guidance on the management of communicable disease outbreaks provides a framework for working across public health structures in local authorities, the NHS and other relevant bodies. Outbreaks of sexually transmitted infections (STIs) present unique challenges for detection, investigation and control and this guidance focuses on the key elements associated with these challenges. This guidance provides an update to previous guidance on managing outbreaks of STIs.

Over the past decade the diversity of STI outbreak investigations that UKHSA has taken part in has expanded. Investigations now include viral infections transmissible through direct sexual contact, such as hepatitis A, mpox and Zika virus. New challenges are also presented by an evolving syphilis epidemic and antimicrobial resistance in Shigella species and gonorrhoea.

Aim and scope

The aim of this updated guidance is to support the detection, investigation, and control of STI outbreaks and the development of local STI outbreak control strategies. This guidance is not intended to provide a complete manual for the investigation of an STI outbreak. Instead, it provides guidance on the major steps, processes and considerations. Links to more detailed information is provided where it is available.

This guidance is relevant to all pathogens transmissible through direct sexual contact.

Who this guidance is for

This guidance is intended for use by any health professionals involved in the detection, investigation and management of STI outbreaks in England. This includes:

  • health protection and field epidemiology professionals at local, regional and national level
  • microbiologists, virologists and clinical laboratory specialists involved with the diagnosis and treatment of STIs
  • GUM clinic and other SHS staff
  • public health professionals and sexual health service commissioners in local authorities or sexual health commissioning groups within the NHS or ICBs

What has changed

A roles and responsibilities section outlines expectations of different organisations and teams and has been updated to reflect current structures.

Guidance on detection is split by the organisation and teams involved. Data sources for potential outbreaks have been updated and expanded. An investigation section includes guidance on assessment of exceedances. A communications section provides guidance for communication messages at different stages of an investigation. Recommendations are listed according to organisation and team.

Background

Data sources for STI outbreak detection

Further details on data sources that can provide signals for potential outbreaks are provided in the UKHSA data guide for sexual health.

UKHSA laboratory surveillance

UKHA operates the laboratory surveillance system SGSS which stores and manages surveillance data on infectious diseases and antimicrobial resistance from diagnostic laboratories across England. SGSS data is considered complete for notifiable infections and is updated daily. However, many STIs are not statutory notifiable infections (including syphilis, gonorrhoea and chlamydia), therefore SGSS data for many STIs is likely incomplete. SGSS also only includes positive test results.

UKHSA have developed a weekly laboratory exceedance algorithm for SGSS data which provides details of exceedances at a regional and national level. The weekly number of laboratory reports for a range of pathogens is presented over the most recent 5 years and the observed number for recent weeks is compared to the expected number given the historical data. Exceedance reports are reviewed weekly by regional Field Service teams.

UKHSA reference laboratories

Data from STI diagnostic and antimicrobial susceptibility testing undertaken at the UKHSA STI Reference Laboratory (STIRL) is available from the Modular Open Laboratory Information System (MOLIS). This includes data on positive and negative test results and where applicable, antimicrobial susceptibility data. MOLIS is a timely source of data and can support outbreak investigations of STIs where the reference laboratories perform routine diagnostic testing for local services, such as for Lymphogranuloma venereum (LGV) as well as identifying cases of multi-drug resistant Neisseria gonorrhoeae. Limited clinical data is collected through MOLIS.

UKHSA Gastro Data Warehouse

Microbiological, genomic, and antimicrobial resistance data is available for Shigella spp. isolates sent to the UKHSA Gastrointestinal Bacterial Reference Unit (GBRU) for confirmation and typing. Data from the GBRU is available in the Gastrointestinal Data Warehouse (GDW). GDW is a timely source of data and can support outbreak investigations of some sexually transmissible enteric infections, such as shigellosis. A weekly report of genetically related clusters is reviewed by UKHSA regional Field Service teams.

GUMCAD STI surveillance system

GUMCAD is the mandatory surveillance system for STIs and collects data on STI tests, diagnoses, and services from all commissioned sexual health services in England. Whilst not real-time, data is reported quarterly to service providers, local authority sexual health commissioners and UKHSA regional teams. Data and reports are available through the UKHSA HIV/STI Data Exchange.

Cleaned, in-year (and therefore provisional) GUMCAD extracts are available quarterly. Whilst every effort is made to ensure these extracts are as complete as possible, occasionally one or more SHS are unable to submit their quarterly data by the submission deadline, affecting the completeness of data extracts. GUMCAD extracts contain demographic and risk factor variables which can assist with understanding the local, regional, and national epidemiology of STIs in England. Further details can be found in GUMCAD data specification and technical guidance.

CTAD chlamydia surveillance system

CTAD is a laboratory surveillance system which collects data on tests and diagnoses of chlamydia as part of the NCSP, as well as data from some local laboratories in England which carry out independent LGV typing. Data tables from CTAD are available quarterly and published annually as official statistics.

Notifications of Infectious Diseases (NOIDs)

Laboratories in England have a statutory duty to notify UKHSA of the identification of notifiable causative agents (including mpox virus, Hepatitis A, B, C, D and E viruses, and Shigella spp.). NOIDs causative agent reports can be used as a source of weekly counts of notifiable organisms, derived from SGSS data. Data is presented for the current week, and the preceding 5 weeks.

Regional surveillance systems

Regional surveillance systems may exist. Notably, certain regions have implemented local enhanced surveillance for syphilis or gonorrhoea during periods of increased incidence. UKHSA regional Field Service teams can advise which systems are available locally and how to access them.

Tools for exceedance detection

Real-time and enhanced surveillance of STIs (RESTI) Snapshot dashboard

The Real-time and enhanced surveillance of STIs (RESTI) Snapshot dashboard uses laboratory surveillance data (from SGSS, MOLIS and GDW) and is updated monthly to provide timely insights into STI trends. Trends of chlamydia, herpes, syphilis, gonorrhoea, syphilis, shigella, LGV and mpox diagnoses are presented for England and by UKHSA region. Data can be viewed by age group and gender. Whilst the numbers of STI diagnoses in SGSS is incomplete, trends follow those seen in GUMCAD, and provide a timely means of monitoring potential exceedances or unusual changes in case numbers. Headline findings are communicated monthly to all users. Access to the dashboard is restricted to UKHSA colleagues working in sexual health and can be requested at [email protected].

Local syphilis metrics dashboard

The Local syphilis metrics dashboard uses GUMCAD data to provide insights into the local epidemiology of syphilis. Testing, diagnosis, and partner notification metrics are available at the local authority, regional and national level and are updated quarterly. Data can be viewed by a number of demographic characteristics and risk factors. Access to the dashboard is restricted to UKHSA colleagues working in sexual health, sexual health commissioners, providers and local authority sexual health leads and can be requested at [email protected].

Roles and responsibilities

A multi-disciplinary response is key to the coordinated investigation of an STI outbreak. Key partners include:

  • sexual health services (SHS)
  • microbiologists, virologists and clinical laboratory specialists
  • local authority public health and commissioning leads
  • NHS and Integrated Care Board (ICB) commissioners
  • primary care organisations
  • communications colleagues
  • UKHSA Field Service, Health Protection Team (HPT) and regional facilitators
  • voluntary sector organisations relevant to the outbreak

Regular meetings should be held across local and regional sexual health networks to raise awareness of changes in testing, health promotion activity, or clinic capacity, as well as to increase the understanding of roles, responsibilities, and capacities. The frequency of meetings should be agreed according to local and regional need and attendance by all partners may not always be required. Partner meetings will also be useful to engage key stakeholders that may be required to investigate an STI outbreak. Members of an OCT may differ from those who are part of sexual health networks for routine monitoring of STIs.

A number of organisations could be involved in the detection of signals for potential STI outbreaks. Once an outbreak has been declared, the role of the OCT is to agree and co-ordinate all activities related to the management, investigation and control of the outbreak.

Depending on the nature of the outbreak, engagement from additional partners may also be required from other organisations such as environmental health, NHS England, ICBs, secure setting staff, social services, police, educational establishments or voluntary organisations.

UKHSA Blood Safety, Hepatitis, STIs and HIV (BSHSH) Division

The BSHSH Division within UKHSA is the national team responsible for surveillance of STIs and bloodborne viruses in England and has subject-matter expertise in this area. The BSHSH Division includes the RESTI team, GUMCAD team, CTAD team and regional facilitator team.

The role of the UKHSA BSHSH Division within an OCT will depend on the circumstances and anticipated impact of the outbreak. For locally focused incidents and outbreaks, representatives from the national team may be required to provide expert advice on the interpretation of information with the national context, the control strategy design and the availability of specialist microbiological services.

Where an outbreak has wider implications for national and international health, meetings are likely to be chaired by a senior consultant from the BSHSH Division who will co-ordinate involvement of other organisations, such as devolved administrations.

UKHSA STI reference laboratory

The UKHSA STI reference laboratory (STIRL) provides specialist and reference services to detect, investigate and characterise clinically important STI pathogens. The laboratory uses established and developmental phenotypic and genotypic assays to define antimicrobial susceptibility of bacterial STIs to relevant antimicrobials for individual case management, as well as for surveillance purposes. STIRL has a role in defining and investigating outbreaks, incidents and diagnostic escape mutants. The laboratory may initially detect and highlight exceedances in sample numbers and/or pathogen profiles, confirm the identify and/or antimicrobial susceptibility profile of outbreak pathogens, as well as assist in establishing local, regional or national laboratory surveillance to investigate outbreaks and incidents. STIRL can provide diagnostic, scientific and clinical advice for outbreaks and incidents.

UKHSA Field Service

The UKHSA Field Service provides regional epidemiological expertise to UKHSA health protection teams, regional facilitators, local NHS, local authorities, and other partners. Regional Field Service teams can undertake detailed analysis of STI surveillance data which can provide early insights into unusual or emerging patterns. Regional field epidemiologists should be involved in the preliminary stages of all exceedance and outbreaks investigations. Field Service teams:

  • monitor routine surveillance data to identify potential outbreaks, including review of UKHSA exceedance reports
  • undertake investigation of exceedance signals
  • lead the analysis and interpretation of data throughout the outbreak investigation, including undertaking analytical studies where appropriate
  • implement enhanced surveillance where required, such as development of questionnaires or surveys and undertaking audits

Where extra capacity is required for data collection (for example, administering questionnaires or data extraction from clinical records), data processing, or analysis, the Field Service Rapid Investigation Team may be able to support the investigation.

UKHSA health protection teams (HPTs)

UKHSA HPTs provide specialist public health advice and operational support to NHS, local authorities and other agencies to prevent and reduce the impact of infectious diseases, chemical and radiation hazards, and major emergencies. HPTs support local disease surveillance and investigate and manage health protection incidents. HPTs:

  • coordinate the inclusion of wider system partners such as environmental health officers
  • provide advice on the identification of potential outbreaks in conjunction with Field Service and regional facilitators
  • provide advice on the management of potential outbreaks through existing disease-specific guidance
  • appoint a consultant in communicable disease control (CCDC) or consultant in health protection (CHP) to chair an OCT

UKHSA regional facilitators

UKHSA regional facilitators provide local intelligence, identification of evidence-based practice and coordinate the involvement of wider system partners. Regional facilitators work alongside Field Service, HPT and local stakeholders to ensure that ongoing monitoring and analysis of regional surveillance data leads to knowledge mobilisation and evidence-based action. Regional facilitators:

  • coordinate the inclusion of wider system partners such as voluntary sector organisations
  • build and maintain relationships with wider system partners
  • provide advice and guidance on the appropriate use of relevant health improvement tools, resources and interventions
  • identify best practice guidance for local health improvement and interventions
  • support development of new health improvement resources
  • liaise with commissioners, sexual health services and voluntary sector organisations regarding public health messaging and outbreak-related campaigns

Sexual health commissioners

Sexual health commissioners within local authorities are responsible for commissioning comprehensive, community-based open access sexual health services in line with national/professional standards. Commissioning responsibilities for SHS in prisons are held by NHSE Health and Justice. Sexual health commissioners have well established relationships with a range of partners and will often lead local area partnership groups. The national integrated sexual health service specification sets out what should be provided by SHS within local authorities. This includes ensuring that:

  • health promotion and prevention activities are commissioned (either directly or sub-contracted)
  • there is sufficient capacity within sexual health services to respond to and manage an outbreak in line with UKHSA guidelines and that this is included within the appropriate contracts, particularly in relation to data collection and sharing
  • there is sufficient funding for any surge capacity or change to service delivery as recommended by an OCT – this is applicable where full responsibility has not been assigned to the service provider (funding levels must also recognise associated costs such as increased laboratory diagnostic tests and capacity)
  • consideration is given to reviewing existing contractual arrangements with service providers if current service specification does not adequately support prevention of future outbreaks
  • findings and experience from outbreak investigations are used to inform future sexual health needs assessments and health improvement activities

Sexual health services

SHS are well placed to identify changes in epidemiology of STIs among their service users at a local level by reviewing service level data on a regular basis (at a frequency determined by need and resources). This enables the timely identification of any changes that may not be detected through routine surveillance. In responding to local outbreaks, sexual health physicians, nurses and health advisers:

  • notify the relevant HPT of any identified increase in diagnoses of STIs, changes in clients being diagnosed with particular infections, or cases of rare infection
  • provide clinical advice on infection presentation and management
  • provide details on patterns of local sexual behaviour and use of specialist SHS
  • assess the capacity of local specialist SHS to respond to any outbreak and raise concerns with commissioners were necessary
  • support the development and collection of enhanced surveillance questionnaires or surveys
  • support the development and implementation of control measures

Voluntary sector organisations

Voluntary sector organisations can help to engage with inclusion health groups such as sex workers, people who inject drugs, people experiencing homelessness and migrant communities. These organisations often represent the views and interests of marginalised population groups and:

  • provide an essential link to population groups that the initial investigation has highlighted as being at increased risk of infection
  • represent the views and interests of the population groups affected
  • facilitate the dissemination of targeted prevention messages
  • contribute knowledge and expertise to facilitate communication between health services and the groups they represent

Other organisations

NHS laboratories

Local NHS diagnostic laboratories can provide microbiological expertise and access to local testing data. Local NHS laboratories ensure relevant isolates are referred to national reference laboratories where required.

UKHSA reference laboratories

Where microbiological typing may help in the investigation of an outbreak, UKHSA reference laboratories provide expert advice on availability and interpretation of typing data.  

Primary care organisations

Primary care organisations (general practice and community pharmacy) may identify or be informed about local STI outbreaks. Dedicated primary care services should contribute towards an OCT if they are aware of individuals who are at increased risk of contracting STIs.

Local authority teams

Dependent on the nature of the outbreak, engagement from wider local authority teams, such as drug and alcohol commissioners, environmental health officers and social services, may be required.

Devolved administrations and international public health agencies

Co-ordination with public health agencies outside of England is the responsibility of the UKHSA BSHSH Division.

Detection

Timely outbreak detection requires regular data reviews to systematically assess surveillance data. Good practice should include reviews of data by commissioners, providers, local authority public health intelligence teams and UKHSA. The frequency of these data reviews should be agreed upon and take place across organisations. UKHSA surveillance systems are not primarily designed for outbreak identification and consequently recognising STI outbreaks may rely on the alertness of local health professionals. 

Data reviews should consider sub-populations of interest as well as different geographical levels, such as local authority or clinic-level. For example, if there is an increase in diagnoses of syphilis among heterosexual men and women whilst the majority of diagnoses have historically occurred among GBMSM, this may indicate a shift in the population at risk.

Exceedance investigations

Possible outbreaks of STIs can be detected and subsequently notified through a number of pathways, depending on the organisation or team which first detects the signal. It is recommended that a review of data sources which may provide signals for outbreaks is undertaken systematically, regularly and according to a standard operating procedure. All exceedances which are detected should be logged, along with the outcome of the investigation. This includes appropriate review and sign-off by a senior member of the team undertaking the review.  

Detection by sexual health services

SHS should regularly review numbers of STI diagnoses and tests. Outbreaks are often detected by clinicians and SHS should use data and their professional judgment to assess the STI exceedance. When indicated, the SHS should complete a STI outbreak notification form and indicate on the form whether the notification is for information or a request for assistance. Communicating the suspected STI outbreak should then occur through appropriate channels.

Detection by sexual health commissioners

Although sexual health commissioners are most likely to receive alerts from SHS, they may also detect exceedances through regular review of data from SHS. Data should be reviewed monthly by sexual health commissioners and follow standard practice to assess the STI exceedance. Any concerns should be promptly discussed with their local HPT and regional facilitator. Notification forms received from SHS should be reviewed and all suspected STI outbreaks communicated.

Detection by UKHSA regional teams

UKHSA regional teams (regional facilitator, HPT and Field Service) should receive all notification forms for suspected STI outbreaks. Review by SHS and sexual health commissioners may indicate that further data analysis is required to assess the STI exceedance. This should include exclusion of other potential causes of increases in disease reports, such as reporting or laboratory diagnostic data errors or changes in reporting. The Regional Facilitator may be aware of local intelligence on any recent changes that may have affected reporting rates, such as local STI awareness raising activities, the establishment of new testing facilities, or changes in testing guidelines or recommendations.

The findings of notable exceedance reviews by UKHSA regional teams should be rapidly communicated (ideally within 7 days) to SHS and sexual health commissioners. To enable timely input into assessment of STI exceedances, UKHSA regional teams should inform the national STI team within the BSHSH division of any suspected outbreak and consider whether it is appropriate to arrange a data review and assessment meeting with national subject matter experts.

Data review by UKHSA regional teams

UKHSA regional teams will undertake regular (ideally monthly) review of all data sources for a signal of a potential STI outbreak. Local and regional STI network or leads meetings should include a standing agenda item to consider all recent assessments of STI exceedances, including communication of the outcomes. Regular data reviews should include:

  • regular review of data within the STI Snapshot Dashboard considering diagnoses of gonorrhoea, syphilis, chlamydia, shigella, LGV, herpes and mpox
  • regular review of the syphilis metrics dashboard considering testing, diagnosis and partner notification at local authority and regional level
  • quarterly review of GUMCAD data considering cases by locality, gender, age and sexual orientation
  • quarterly review of CTAD data considering chlamydia diagnoses by locality, gender and age
  • regular review of sexually transmitted Shigella spp. clusters included in the weekly Shigella report provided using data from the UKHSA Gastro Data Warehouse

Assessment of STI exceedances

Consider the following when assessing the likelihood that an exceedance represents an outbreak:

  • are the diagnoses within a specific population or geographical location that can be defined as an outbreak?
  • is the increase in diagnoses above that normally expected and cannot be explained by changes in testing or availability of services?
  • has there been a change in the population at risk that could explain increased diagnoses?
  • is there a cluster of treatment failures in time, a geographical location or a specific population subgroup?
  • is there a cluster of infections where there was a change in clinical presentation or severity?

Further investigation into a potential outbreak may require a multi-disciplinary group, either as part of the OCT or prior to escalation. This group should consider what information is required to determine if the signal represents a cluster or an outbreak.

Escalation following exceedance detection

Immediately following agreement by all relevant partners (always including the UKHSA HPT, regional facilitator and Field Service team, together with SHS and commissioners covering the population at risk) that there is evidence of a potential outbreak, the investigation should move to the investigation stage. This includes rapidly establishing an OCT and commencing the epidemiological investigation.

Investigation

Preliminary investigation

Is it an exceedance, cluster or outbreak?

An exceedance occurs when the counts of a particular event exceed a threshold based on historical comparisons and may occur due to a number of factors. An STI cluster occurs where multiple cases are linked by proximity in time and geography. These may reflect cases with a similar predominate risk factor or drawn from the same population group. An STI outbreak is a special case of a cluster where a known epidemiological link has been established.

Assessment of STI exceedances is likely to need additional clinical and epidemiological intelligence and data to consider the potential epidemiological link between cases or underlying cause. This may require co-ordination between organisations. The critical intelligence gathering required will depend on the characteristics of the signal under investigation and where it was detected. Local knowledge of service delivery from SHS and commissioners may help inform assessment.

Recognition of unusual activity by sexual health services

Clinical or diagnostic staff within SHS may observe unusual patterns in clinical presentations or diagnoses of an STI. This could occur in a specific population group, area, or be linked to a specific venue.

Detection of an exceedance in surveillance data

Regular data reviews by UKHSA teams may indicate exceedances in case numbers that require further investigation. Preliminary investigations to establish an epidemiological link should consider what routinely collected data on exposures is available, including enhanced surveillance questionnaires. Exposure data may indicate attendance at a specific location or setting which may require follow-up by the local HPT.

Detection of an emerging pattern of virulence or antimicrobial resistance  

Regional and national microbiological services may identify the emergence of a new sexually transmissible pathogen or changes in the virulence or resistance pattern of an existing pathogen which may require investigation.

Informing the local health protection team (HPT)

When aware of a potential STI outbreak, SHS and/or sexual health commissioners should notify the local HPT and regional facilitator at the early stages of an investigation, irrespective of the nature of the alert and the detection setting. This will ensure an OCT is established if necessary and appropriate public action can start as soon as required.

Role of the Outbreak Control Team (OCT)

Once the epidemiological link between cases has been established, an outbreak should be declared, and an OCT convened. Other special circumstances, such as a general increase in diagnoses or a case of multidrug-resistant infection, may require an OCT to be established. Guidance is available for the management of ceftriaxone-resistant N. gonorrhoeae.

The role of the OCT is to agree and co-ordinate all activities related to the management, investigation and control of the outbreak. UKHSA provides detailed operational guidance for communicable disease outbreak management. Local outbreak plans should enable responses to be instigated as a directed by an OCT. As OCT meetings may include discussion of individual cases, confidentiality of individuals should be maintained throughout all discussions.

Data collection and descriptive epidemiology

Case definitions

An initial case definition should be immediately agreed by the OCT based on what is known about the infection and population at risk. A case definition should include elements of time, place and person. The definition should distinguish outbreak-associated cases from those likely not to be associated with the outbreak. Case definitions may include specific risk factors (for example, attendance at a certain venue), population groups (for example, GBMSM) or microbiological characteristics (for example, infection with an organism with a defined genetic profile). Case definitions may reflect different levels of certainty related to inclusion in the outbreak.

As the investigation progresses the case definition should be regularly reviewed by the OCT and revised as necessary. General principles should be to use a sensitive case definition initially that can be modified to become more specific as the epidemiological picture becomes clearer during the investigation. For example, this may mean restricting the definition to include cases from a more specific geographical area or time period.

Working hypotheses

It may be possible to form a preliminary hypothesis from the initially gathered information and what is known about the population at risk. Alternative explanations should not be excluded prematurely as these may include infection acquired through an alternative route or broader epidemiological shifts. Such a shift was seen with mpox during the 2022 outbreak where transmission occurred through direct sexual contact rather than associated with contact between animals and humans.

When sufficient data and intelligence has been collected, the OCT may consider implementing an analytical study to enable hypotheses to be formally tested. Hypotheses should be reviewed at each OCT meeting.

Outbreak line lists and data collection

Following declaration of the outbreak, a case line list should be created immediately. This should be managed by the team responsible for the epidemiological investigation but will require input from different organisations represented at the OCT, notably SHS and other clinical services. For the majority of outbreaks, the UKHSA regional Field Service team would be responsible for the outbreak line list.

In the absence of standard surveillance forms, it may be necessary to create a questionnaire or data extraction form to capture important clinical and epidemiological data for each case. The regional Field Service team can produce and distribute questionnaires in a variety of formats, including electronic surveys which can be accessed via mobile devices. Where there are gaps in information or understanding of risk factors, detailed interviews with cases may help to elicit more contextual information about the social context of the outbreak. Such an approach has been used successfully during an outbreak of sexually-transmitted shigellosis.

If necessary, cases can be reinterviewed using enhanced questionnaires to gather more detailed information on risk factors and contacts. The local Field Service team can create the questionnaires and, due to their sensitive nature, the interviews are often conducted by the sexual health provider.

The law allows patient information to be shared with other health professionals in the interests of controlling spread of infectious diseases. Within this framework, local authorities, SHS, and UKHSA can work effectively together, while adhering to appropriate information governance policies when sharing data.

Case finding

Case finding should be focused on the population at risk and both active and passive approaches may be required. Passive case finding should use all suitable data sources for STI outbreak detection. This should include consideration of receiving data extracts from SHS or monthly returns of GUMCAD data.

Active case finding may require co-ordination of testing or screening activities and should be considered as part of secondary prevention measures. If the population at risk is too large for focused public health action, social contact interviews may be an effective approach to find individuals that could benefit from screening. This approach has been used successfully in relation to a resurgence of gonorrhoea and syphilis in Baltimore, United States.

Epidemiological investigation

The UKHSA Field Service team should produce a descriptive epidemiological summary for consideration at each OCT. This should be based on data included in the outbreak line list. New information from the previous summary should be highlighted in yellow. The Field Service Rapid Investigation Team is also available to support field investigations.

The descriptive epidemiological summary should as a minimum include:

  • a summary of the situation including key developments
  • the distribution of cases by time (epidemic curves)
  • the distribution of cases by place (dot maps or other as appropriate)
  • the distribution of cases by case characteristics (tables and/or figures to describe the distribution of age, gender and other risk factors)
  • a connected network diagram indicating epidemiological links between cases (such as known sexual contact or attendance at venues or settings)

Interpretation of any trend in case numbers during an outbreak should take account of changes in each or a combination of:

  • awareness
  • health seeking behaviour
  • service access
  • intervention coverage

A decline in reported cases may be explained by a reduction in attendance patterns or testing coverage, for example. If case-finding initiatives such as the expansion of STI screening were introduced, case numbers may initially remain stable or even increase. In this situation, measure of the positivity within the target population is recommended as a useful additional primary outcome measure. 

Microbiological investigation

Depending on the incident, and especially if treatment failures have occurred, the local CPHI or the STI or gastrointestinal reference microbiologist could be contacted to discuss the referral of specimens for confirmation or additional testing, such as molecular typing or extended antimicrobial susceptibility testing. Typing results can indicate likely transmission links or subclusters which will help inform the control strategy. Apart from enteric STIs (such as Shigella spp.), samples are not routinely sequenced. If, however, the outbreak is associated with antimicrobial resistance, relevant colleagues in the STI reference laboratory should be consulted so that support with sequencing can be discussed where necessary.

Analytical studies

Analytical studies may be conducted to test hypotheses generated during the investigation. Criteria and further information on conducting analytical studies during outbreak investigations is available. Epidemiological analysis to support hypotheses can create stronger evidence to justify control measures. Analytical studies can be particularly helpful if investigating cases with unusual characteristics or a new STI, such as the use of a case-control study to investigative risk factors for LGV among GBMSM. Other approaches to analysis can be used in the investigation of STI outbreaks, such as geospatial methods for STI outbreak investigations.

Regional Field Service teams have extensive experience in conducting analytical studies and will lead on the design and implementation of these studies. However, the OCT should consider the need to balance resources against the expected success and benefit of conducting an analytical investigation.

Control measures

Control measures are aimed at preventing and reducing onward transmission of infection, thereby limiting any ongoing outbreak and protecting health. STI outbreaks are challenging to investigate and control because they are strongly associated with sexual contact and sexual network structures.

The response and control measures considered by the OCT are likely to include a mix of primary and secondary prevention measures and will vary depending on the specific infection and population groups involved. Multi-disciplinary co-ordination of control measures is vital for success in reaching the target population and ensuring effective control. Many of these control measures will be delivered directly by SHS or voluntary sector organisations.

Budgetary considerations related to the implementation of control measures are outside the scope of this guidance but should be discussed and agreed by the OCT, as per usual arrangements for the management of outbreaks of infectious diseases.

Primary prevention measures

Management of cases

Effective clinical and public health management of cases of an STI are central to minimising the long-term impacts of disease and preventing onward transmission. Management will depend on the specific infection but may include:

  • antibiotic therapy
  • exclusion
  • completion of enhanced surveillance questionnaires

The management of individual cases will largely be undertaken by the relevant SHS but may be supported by the HPT depending on the specific infection. Providing appropriate information on safe sexual practice should be a feature of the management of all STIs.

The OCT should also consider whether there are any safeguarding concerns relating to the incident or outbreak and consider appropriate actions. This should be particularly considered when managing vulnerable population groups, for example, sex workers, younger age groups, or migrant populations.

Education and awareness raising

This may include the routine sharing of general information on promoting good sexual health, such as that produced by national or local partners. Targeted information should also be considered and will include information addressing actions for a particular population group at increased risk of infection, measures to reduce transmission of a particular infection and signposting to other services.

Information should be appropriate for the relevant population at risk and may be supported by national, regional or local media messaging as well as local measures which can be disseminated through community networks and should include signposting to relevant specialist services. Voluntary sector organisations can support targeted awareness raising for certain populations.

Specific consideration should be given to control measures at sex-on-premises venues. Local UKHSA HPT and Regional Facilitator leads can access specific guidance for this setting.

Outreach services

If a specific population at risk has been identified, the OCT may consider whether outreach services can be stood up in specific venues or settings. These settings commonly include named venues associated with the outbreak, such as sex-on-premises venues, clubs and other social settings. Outreach services can provide diagnostic and clinical services, alongside awareness raising, promotion of safe sex messaging, information and advice, condom provision, and signposting to other specialist services. Use of a mobile unit should be considered where access to the population at risk may not be possible through specific venues or settings.

Secondary prevention measures

Case finding

Active case finding according to the agreed case definition for the investigation will form part of the epidemiological investigation. If there is evidence of ongoing transmission, despite the implementation of primary prevention measures, the OCT should consider additional case finding approaches for the population at risk. The decision to start active case finding will depend on the characteristics of the outbreak, including the number of cases, potential for high numbers of undiagnosed cases, health impacts of the infection as well as anticipated success of primary prevention measures.

Case finding approaches may include targeted testing at settings or venues associated with the outbreak, which may be best delivered through local outreach services. This may be at prisons, treatment centres, drug facilities, bars and clubs, and homeless shelters. Awareness campaigns may also be considered to encourage testing, these may include communications material distributed at specific venues or settings.

Extension of recommendations for existing screening programmes may require operationalising at a national or regional level. The OCT may further consider recommendations to UKHSA and NHSE. Enabling online requests for STI testing for the population at risk should be considered if appropriate.

Partner notification

Partner notification (PN) plays a critical role in identifying individuals who have been potentially exposed to an STI, diagnosing undetected infections and limiting spread. PN also provides information on sexual networks and potential routes of transmission, aiding the epidemiological investigation.

PN can be challenging where the population at risk report high numbers of anonymous or uncontactable sexual partners. Stigma and concerns about confidentiality may be significant challenges to successful PN. As such, the OCT will need to review the effectiveness of PN as a control measure and to continually consider whether other measures, such as wider active case finding, may be more effective.

PN is most likely to be carried out by the SHS, but the OCT should consider whether existing resources are sufficient for the response and whether additional commissioning arrangements need to be sought. The OCT should consider the most appropriate tool for PN, including the use of novel digital platforms for anonymous notification.

Vaccination

For some infections associated with sexual transmission, including Hepatitis A, Hepatitis B and mpox, pre-exposure vaccination is available and may be available to individuals at high risk of transmission. UKHSA publishes guidance on use of vaccination for specific infectious diseases during outbreaks. The latest information on vaccine and vaccination procedures are included in national information for public health professionals on immunisation.

In an outbreak setting, a targeted vaccination programme may be offered. In addition, passive and/or active vaccination may be recommended for groups of individuals or sexual contacts of cases and will be guided by the OCT through the input of the local HPT and UKHSA national STI team. Such control measures may be critical for control, such as the targeted mpox vaccination programme for GBMSM that played a key role in the UK control strategy for the 2022 outbreak.

The OCT may consider the delivery of a locally targeted vaccination programme based on the epidemiology of the outbreak and should consider how best to deliver this to maximise uptake. The co-ordination and delivery of such initiatives is likely to fall within the remit of NHSE who should be included as part of the OCT membership where required. For example, the regional management of an outbreak of Hepatitis A associated with sexual transmission amongst heterosexual women may suggest an extension to the recommendations for pre-exposure vaccination. Such recommendations would need consideration by national experts, including the JCVI.

UKHSA infection-specific guidance includes recommendations for the public health management of contacts of cases and should be referenced alongside national information for public health professionals on immunisation.

Evaluation of interventions

In addition to ongoing monitoring of case numbers as part of the epidemiological investigation, the OCT may consider additional evaluative measures for evaluation of the effectiveness of any interventions.

Evaluation measures

The OCT should define the primary outcome measures for evaluation during the early stages of the investigation. These may include: 

  • the number, range, coverage, and type of health promotion interventions
  • awareness among the target population of health promotion interventions
  • proportion of the target population engaging with the intervention
  • frequency and coverage of the intervention
  • intervention uptake by the target population
  • proportion of the target population offered STI screening tests
  • uptake and coverage of STI screening tests by the target population

Process measures can evolve during an investigation, reflecting changes to intervention strategies and case definitions. The investigation of gonorrhoea in young heterosexual adults explored the selection of process measures in detail, particularly in relation to awareness raising strategies.

Measuring awareness and engagement

Options include:

  • undertaking brief surveys of clinic attendees before, during and after interventions
  • web-based surveys disseminated through social media
  • counting numbers of ‘click throughs’ from banner ads or website hits

It may be possible to monitor uptake and coverage of interventions using routine data sources and more detailed local enhanced surveillance from clinical services, routine laboratory reports, or reference laboratory reports.

A useful framework to evaluate the effectiveness of a particular intervention can be found as part of evaluation resources for sexual health, reproductive health and HIV services.

Declaring the outbreak over

The OCT is responsible for declaring the outbreak over. The decision to declare the outbreak over should be informed by on-going risk assessment. Agreement that an outbreak is under control should include consideration of:

  • an observed stabilisation and/or a decline in case numbers (a return to expected levels)
  • a decrease in case numbers to levels which can be managed through routine clinical and public health services
  • high coverage of effective interventions (such as screening and/or vaccination) in the population at risk

This decision should include consultation with the appropriate DPH. Rationale of the decision should be included in the minutes of the final OCT meeting and may include whether long-term preventative measures are required. The OCT should consider the need for a period of enhanced surveillance following the end of an outbreak to provide assurance that any resurgence will be closely monitored.

Outbreak report

A detailed outbreak report should be written as part of communicating the findings of the investigation. UKHSA operational guidance for communicable disease outbreak management includes details of what should be included in an outbreak report. The report should be disseminated to a distribution list agreed by the OCT within 12 weeks of closure of the outbreak.

Outbreak debrief and lessons learned

Following the final OCT meeting, key members of the OCT should meet to review the management of the outbreak, identify lessons learnt and to agree recommendations for preparedness and management of future outbreaks. Debriefs form part of standard practice following the conclusion of significant outbreaks, conducted according to UKHSA operational guidance for communicable disease outbreak management.

Communication

Communications should consider of the most effective method for reaching the target audience throughout an STI outbreak investigation. Communications should be reviewed at each meeting for the OCT. Sensitive communications reflecting the need to handle sexual information delicately and confidentially play a central role in the successful management of STI outbreaks. The OCT will agree a communications strategy that reflects these sensitivities.

Appropriate communications should be made at 3 main stages in the investigation of a confirmed or suspected STI outbreak:

  1. Following recognition of the signal.
  2. During the outbreak investigation.
  3. Once the outbreak investigation has concluded.

Informing system partners of a signal

What to communicate

The initial notification of the signal should include all relevant data collected as part of the clinical and epidemiological investigation. Where possible, a brief descriptive epidemiological summary should be distributed.

Who should be involved

Communication routes will depend on the team who have detected and investigated the exceedance. Teams should aim to inform system partners about suspected and confirmed outbreaks at the earliest opportunity. UKHSA regional teams should ensure that all communications for potential outbreaks should be shared internally (with the HPT, Field Service and Regional Facilitator) and externally (SHS and sexual health commissioners). Where detection of a suspected outbreak is through sexual health commissioners or SHS, prompt communication with all UKHSA teams should be made alongside all other local commissioners and providers.  

Where outbreaks include cases outside of England, communications with partner organisations should be led by the UKHSA national STI team.

When should it be communicated

Notifications of potential outbreaks should be communicated to system partners as soon as possible. The potential severity of the outbreak should be prioritised above uncertainty in the validity of the signal.

Communications during an STI outbreak investigation

What to communicate

The communications strategy, including audiences, will depend on the nature of the incident, and will include consideration of engagement with stakeholders, online content and media.

Where relevant, communications to the general public should consider any impact of digital exclusion. Translation to languages commonly used by target populations should be considered, particularly where literacy in English is considered a potential barrier. Suitable language to minimise stigma around sexual orientation and sexual behaviour should be considered and used appropriately in all communications.

Effective communication will maximise community engagement and uptake, improving the effectiveness of control measures for the impacted population, as well as ensuring stakeholders hold a common vision and understanding of the management of the outbreak.

Who should be involved

During an outbreak investigation, the OCT will have responsibility for agreeing all communications related to the outbreak. UKHSA Communications Managers and local authority Communications Managers will agree a communications strategy and work to co-ordinate and oversee its delivery. There are several voluntary and community sector organisations that can offer support to the OCT on communication and media messaging and can help to access particular population groups.

When should it be communicated

The OCT will agree at which stages of the investigation communications are necessary. The timing of communications will depend on the ongoing risk assessment, including the potential impact and severity.

Outbreaks of considerable public health interest (such as emergent organisms, novel drug-resistance profiles, or clinically severe infections) should be considered for publication or conference presentations prior to the conclusion of the investigation.

Communicating the findings of an STI outbreak investigation

What to communicate

An outbreak report should always be written following the conclusion of the investigation. The Chair of the OCT will have responsibility for completion of the report. UKHSA operational guidance for outbreak management includes details of what should be included in an outbreak report.

Scientific or public health communications to professional groups through conferences and/or peer-reviewed publications should be agreed by the OCT. Important new knowledge and learning, including the use of and effectiveness of control measures, should be considered for dissemination.

Who should be involved

The OCT will agree all communications following the conclusion of an outbreak investigation. Abstracts and scientific papers may require organisational review before they can be submitted for publication. UKHSA has an internal portal for review of all articles which can be accessed via the intranet.

When should it be communicated

Outbreak reports should be written following closure of the investigation by the OCT. Conference presentations or peer-reviewed articles should be delivered/published as soon as is practical.

UK Health Security Agency briefing notes

Where an outbreak or cluster may have operational significance for staff and organisations, the OCT should consider producing a UKHSA briefing note to:

  • provide assurance that an incident is being contained with no wider implications
  • raise awareness of actions that staff may need to take
  • inform ongoing action

Once authorised, UKHSA briefing notes can be distributed outside of UKHSA by email cascade.

Definitions

Exceedance

An exceedance occurs when the count of reports of a particular organism exceeds a threshold that is based on historical comparisons. This could occur due to a number of factors, including:

  • a change in laboratory testing methods
  • batch reporting to a surveillance system
  • coding changes at a local laboratory
  • duplicate laboratory reports reported to a surveillance system
  • a change in clinical practice, for example implementation of a policy to target screening of a particular group
  • detection of a real outbreak or cluster

Cluster

A cluster is defined as 2 or more cases with onsets of symptoms (or laboratory testing dates if onset dates are not available) that are close in time and/or place. Following investigations, a cluster may be found to be sporadic (coincidental cases that are close in time and space but not epidemiologically linked). Conversely, further evidence may include a common epidemiological link, suggestive of an outbreak.

Outbreak

UKHSA operational guidance for communicable disease outbreak management uses the following definitions for an outbreak:

  • an incident in which 2 or more people experiencing a similar illness are linked in time or place
  • a greater than expected rate of infection compared with the usual background rate for the place and time where the cases have occurred
  • a single case for certain rare or high-consequence diseases (although the actions outlined in this guidance may not all be applicable)
  • a suspected, anticipated or actual event involving microbial contamination of food or water

Before an outbreak is declared, it is important to exclude other potential causes of increases in infection reports, such as reporting artefacts or changes in testing policy, when assessing all STI exceedances. Many cases and clusters are handled within routine HPT operations and will not require an OCT to be convened.

Population at risk

The population at risk is those persons who are considered to be at high risk of developing the STI of interest. It is important to consider the key epidemiological elements of time, place and person in defining the population at risk. An example of a defined population at risk would be persons who have attended or are likely to attend a specific venue in a given calendar year.

Recommendations

The UKHSA Field Service should:

UKHSA health protection teams should:

  • attend regular meetings across local and regional sexual health networks
  • participate in monthly review of STI data sources in collaboration with other regional stakeholders
  • ensure all communications for potential outbreaks are shared with the Field Service, regional facilitators and external partners (SHS and sexual health commissioners)
  • promptly inform the UKHSA BSHSH team of all suspected outbreaks
  • consider convening an OCT for each STI outbreak and ensure necessary stakeholder representation
  • appoint a consultant in communicable disease control (CCDC) or consultant in health protection (CHP) to chair an OCT

UKHSA regional facilitators should:

Sexual health commissioners should:

Sexual health services should:

Appendices

Appendix 1: Case study

Appendix 2: STI outbreak notification form

Acknowledgements

Authors

Hannah Charles, Vicky Dowling, Lynsey Emmett, Gareth Hughes, Charlotte Jackson, Holly LeBlond, Soeren Metelmann, Emma O’Brien, Norah O’Brien, Shahin Parmar, Ian Simms, Gemma Ward.

Contributors

Sarah Atkinson, Michelle Cole, Alison Critchell, Kate Donahoe, Kirsty Foster, Kate Holburn, Kathryn Hopkins, Leifa Jennings, Tony Proom, Katy Sinka, Georgina Wilkinson.

Important contacts

UKHSA health protection teams

UKHSA Field Service teams

UKHSA Blood Safety, Hepatitis, STIs and HIV (BSHSH) Division

UKHSA STI reference laboratory

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