Research and analysis

Group A streptococcal infections: report on seasonal activity in England, 2024 to 2025

Published 31 October 2024

Applies to England

Main points

Scarlet fever activity in England, for the first six weeks of the 2024 to 2025 season, is in line with normal seasonal patterns with GP consultations increasing. Laboratory notifications of invasive group A streptococcal (iGAS) infection are similarly within normal levels for the time of year.

Given the potential for severe presentations, scarlet fever cases should be treated promptly with antibiotics to limit further spread and reduce risk of potential complications in cases and their close contacts. Clinicians should continue to be alert to the severe complications of GAS infections and maintain a high degree of clinical suspicion when assessing patients, particularly those with preceding viral infection (including chickenpox) or their close contacts.

Updated UK public health guidance on the management of close contacts of iGAS cases in community settings was published on 15 December 2022, with public health action extended to include patients with probable invasive GAS infection and additional close contact groups recommended for antibiotic prophylaxis.

National guidance on the management of scarlet fever outbreaks highlights essential tools to limit spread: prompt notification of scarlet fever cases and outbreaks to UK Health Security Agency (UKHSA) Health Protection Teams (HPTs); collection of throat swabs (prior to commencing antibiotics) when there is uncertainty about the diagnosis and exclusion of cases from school and work until 24 hours of antibiotic treatment has been received.

Numbers presented in this report are based on data available as of 23 October 2024 for diagnoses up to and including 20 October 2024 (end of week 42). Numbers presented may change as updated data becomes available.

Key definitions are available at the end of the report.

Scarlet fever

Scarlet fever data presented in this report are based on GP in-hours sentinel surveillance data due to processing delays for scarlet fever notifications, following the roll-out of a new national case and incident management system.

The first 6 weeks of the 2024 to 2025 season have seen a slight increase in rates of in-hours GP consultations for scarlet fever in line with normal seasonal patterns, reaching 0.65 per 100,000 population in week 42, October 2024. This falls within the range (0.02 to 1.54) observed for the same week in the last 6 seasons (2018/19 to 2023/24).

Figure 1. Weekly scarlet fever GP in-hours consultation rate in England, by season, 2018 to 2019 season onwards

Note: Data shown for the current season goes up to week 42 (18 October 2024).

Invasive group A streptococcal infection

Laboratory notifications of iGAS infection in the first 6 weeks of the 2024 to 2025 season (weeks 37 up to week 42) are comparable to those typically seen at this point in the season (Figure 2). A total of 229 notifications of iGAS disease have been received, with a weekly high of 44 notifications in week 37 (9 September 2024 to 15 September 2024). Laboratory notifications of iGAS infections so far this season are higher than average (180) but within the range (80 to 280) for the same period in the prior 6 seasons (2018/19 to 2022/23).

So far this season, the highest notification rates were in the North East (0.7 per 100,000 population), followed by Yorkshire and the Humber (0.6), and London (0.4).

Figure 2. Weekly laboratory notifications of iGAS, England, by season, 2018 to 2019 season onwards

Note: Numbers of notifications in the latest weeks of the 2024/25 season are expected to increase due to a lag in laboratory reporting. The decline in notifications in recent weeks should be interpreted with caution; delayed processing and reporting timeframes are represented by a dashed line between weeks 41 and 42 of 2024.

Of reports received this season to date, rates were highest in those aged 75 years and older (1.4 per 100,000), followed by those under 1 year (0.7), and 65 to 74 year-olds (0.5). The lowest notification rate was observed in 10 to 14 year-olds, 0.2 per 100,000. Early seasonal trends in case rates for different age groups are broadly consistent across seasons, except for the unusual pattern noted among children in the 2022/23 season (1, 2).

The median age of patients among notified cases of iGAS so far this season is 57 years (range of 0 to 102 years). This is broadly consistent with prior age ranges reported for this point in the preceding 6 seasons (51 to 59 years).

Antimicrobial susceptibility results obtained from routine laboratory surveillance of iGAS isolates in 2024 so far (week 1 to 42) were broadly consistent with prior years. Specifically:

• isolates were reported as universally (100%) susceptible to penicillin
• 6% were resistant to clindamycin (compared with 5% last season; range 5% to 13% in the last 5 years)
• 11% of isolates were resistant to erythromycin (compared to 7% in 2023; range 6% to 15% in the last 5 years), and
• 25% were resistant to tetracycline (compared to 18% in 2023; range 18% to 39% in last 5 years)

Analysis of reference laboratory iGAS isolate submissions indicated a diverse range of emm gene sequence types identified so far in 2024 (January to September 2024). The results indicate that emm 3 is the most common type so far (17.8% of all referrals), followed by emm 1 (8.3% of referrals); emm 6 is the next most commonly isolated, with 7.7% of referrals.

Discussion

The 2022/23 season season saw a period of considerable elevation in scarlet fever notifications (1, 2) and unusual seasonal patterns, also seen GP in-hours consultation rates (3). In comparison, the 2023/24 season saw a return to more usual seasonal patterns. At this early point in the 2024/25 season, scarlet fever rates are in line with seasonally expected patterns

The 2022/23 season saw exceptional levels of GAS activity leading to a large volume of scarlet fever notifications creating a backlog in processing. Estimated notification numbers were published pending completion of processing of the backlog of notifications. A review following this completion has revised the previously reported notifications from 61,442 to 43,968 cases in England for the 2022/23 season. This change would not have altered the public health response and advice given at the time given it still represents exceptional scarlet fever activity. Laboratory notifications of iGAS infection were not affected by a processing delay and similarly showed exceptional activity during the 2022/23 season. A web-based notification app (eNOIDS) has since been developed to obviate the need for manual entry of scarlet fever notifications, reducing the risk of this issue occurring in future.

Cases of iGAS infection in the first part of the current season are following a normal seasonal pattern. Incidence remains below the high levels recorded in 2022 and the total to date in the 2024/25 season is below the level seen in the previous 2 seasons. The pattern of weekly laboratory notifications and age group distribution are within the range typically expected.

So far this season emm 3 is the most common gene type, a continuation from the previous season where emm 3.93 became the most dominant circulating type.

Prompt treatment of scarlet fever with antibiotics is recommended to reduce risk of possible complications and limit onward transmission. GPs and other frontline clinical staff are also reminded of the increased risk of invasive disease among household contacts of scarlet fever cases (4, 5). Clinicians should continue to maintain a high index of suspicion in relevant patients for invasive disease as early recognition facilitates prompt initiation of specific and supportive therapy for patients with iGAS infection.

Relevant guidelines and FAQs are available on GOV.UK as follows:

• guidelines for the public health management of scarlet fever outbreaks in schools, nurseries and other childcare settings
• factsheet: scarlet fever: symptoms, diagnosis and treatment
• guidelines for the management of close community contacts of invasive GAS cases and the prevention and control of GAS transmission in acute healthcare and maternity settings
• prevention and control of group A streptococcal infection in acute healthcare and maternity settings
• Report a Notifiable Disease (eNOIDS)
• weekly notifiable disease reports are published each week for a timelier update
• blog: group A strep – what you need to know

All invasive disease isolates – and also non-invasive isolates – from suspected clusters or outbreaks should be submitted for typing to:

Staphylococcus and Streptococcus Reference Section
Antimicrobial Resistance and Healthcare Associated Infections (AMRHAI)
UK Health Security Agency
61 Colindale Avenue
London
NW9 5HT

Data sources and methods

Scarlet fever data is presented as GP in-hours consultation rates per 100,000 registered population. This information is collected from UKHSA’s GP in-hours syndromic surveillance system; this system is sentinel, which means that not all GP practices in England are included, and coverage varies by UKHSA region, so comparison between geographic regions is not recommended. The system currently includes approximately 19 million registered patients across England. The data included is from two sources: TPP and ORCHID (Oxford and Royal College of General Practitioners Clinical Informatics Digital Hub). The indicator for scarlet fever syndromic is based on diagnoses recorded during GP in-hours patient consultations, and diagnoses are based on signs/symptoms and may not be laboratory confirmed. The weekly rates presented differ from the daily rates reported as standard elsewhere (6).

Invasive GAS laboratory notification data was extracted from the UKHSA Second Generation Surveillance System (SGSS) and combined with specimen referrals to the Staphylococcus and Streptococcus Reference Section to produce a total number of episodes for England. Data was extracted on 23 October 2024.

An improved method of patient iGAS episode de-duplication has been implemented for this season and will be applied for all subsequent reports. The new method corrected an error which resulted in a small number of records being counted more than once in the iGAS episode analyses in the prior reports. The new method led to a less than 1% reduction in iGAS episodes recorded in the 2023/24 season, some regions have been impacted more than others in the earlier seasonal update reports. Please refer to the appendix table associated with this report for a detailed comparison.

A season runs from week 37 in one year to week 36 in the following year (mid-September to mid-September). The 2024/25 season data within this report covers 9 September 2024 to 20 October 2024.

Population rates are calculated per 100,000 using the relevant year’s ONS mid-year population estimate.

The M protein gene (emm) encodes the cell surface M virulence protein. Information for the emm gene, for this report, was extracted from UKHSA’s reference laboratory and contains data between 1 January 2024 until 30 September 2024.

Prior to the COVID-19 pandemic, there were a number of seasons when elevated incidence of scarlet fever and iGAS was seen, in particular the 2017 to 2018 season. During the pandemic there was an unprecedented reduction in the number of scarlet fever and iGAS notifications, affecting the 2019 to 2020 season and the 2021 to 2022 season.

References

1. UKHSA (2023). Group A streptococcal infections: 15th update on seasonal activity in England

2. Guy R, Henderson KL, Coelho J, Hughes H, Mason EL, Gerver SM, and others (2023). ‘Increase in invasive group A streptococcal infection notifications, England, 2022’ Eurosurveillance: volume 28, number 1

3. UKHSA (2023), GP In-hours Syndromic Surveillance System Bulletin (England): 2023, week 21

4. Lamagni T, Guy R, Chand M, Henderson KL, Chalker V, Lewis J, and others (2018). ‘Resurgence of scarlet fever in England, 2014 to 2016: a population based surveillance study’ The Lancet Infectious Diseases: volume 18, number 2, pages 180 to 187

5. Watts V, Balasegaram S, Brown CS, Mathew S, Mearkle R, Ready D, and others (2019) . ‘Increased risk for invasive group A streptococcus disease for household contacts of scarlet fever cases, England, 2011 to 2016’ Emerging Infectious Diseases: volume 25, number 3, pages 529 to 537

6. UKHSA (2024). Syndromic Surveillance Systems and Analyses

Acknowledgements

These reports would not be possible without the weekly contributions from microbiology colleagues in laboratories across England, without whom there would be no surveillance data. Feedback and specific queries about this report are welcome via [email protected]