Research and analysis

Group A streptococcal infections: third update on seasonal activity in England, 2023 to 2024

Updated 25 July 2024

Applies to England

In the first 22 weeks of the 2023 to 2024 season (week 37 to week 6), scarlet fever notifications followed a typical seasonal pattern, though numbers of notifications were at the higher end of what is normally expected. Notifications showed a moderate December peak followed by a drop-off after the Christmas break and showing a steady rise in line with the usual seasonal patterns up to week 6. Scarlet fever notifications in the latest week are at a similar level to this point last season.

Similarly, the incidence of invasive group A streptococcus (iGAS) disease increased to a peak spanning week 52 and week 1, in line with what would normally be expected for the time of year. The age distribution of cases is following expected patterns, with most being older adults. This contrasts with the 2022 to 2023 season when high rates of iGAS infection in children were observed in the early part of the season (1).

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 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.

New NHS England best practice principles to support clinicians when assessing patients presenting with a direct-to-consumer point-of-care device results for GAS were published on 19 January 2024

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, namely:

• 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
• exclusion of cases from school and work until 24 hours of antibiotic treatment has been received

Data presented within this seasonal activity update is based on information available as of 20 February 2024 and covers notifications up to 11 February 2024 (the end of week 6). Numbers presented in this report may change as updated data becomes available. Weekly notifiable disease reports are published each week throughout the year to provide a regular update of scarlet fever notifications.

Key definitions are available at the end of the report. Seasons extend from week 37 (mid-September), of one year, to week 36 (mid-September) of the next.

Scarlet fever

In the current 2023 to 2024 season, scarlet fever notifications remain slightly higher than would normally be expected for the time of year. However, notifications are considerably lower than those observed during the 2022 to 2023 season (see Figure 1). Notifications increased from 457 in week 52 of 2023 to 1,277 in week 5 of 2024, suggesting the start of increased activity that typically peaks in the spring.

A total of 12,503 notifications have been made so far in the current season (up to and including week 6 of 2024), with 7,044 in 2024. Compared to the previous 5 seasons (2017 to 2018 season to the 2021 to 2022 season), this is outside the range (532 to 5,584) and higher than the average (3,240).

Scarlet fever notifications for the 2022 to 2023 season remain provisional while the notifications of infectious diseases (NOIDs) annual report is being compiled. As a result, numbers may change in future reports.

Figure 1. Weekly scarlet fever notifications in England, by season, 2017 to 2018 onwards

Note: data shown for the current season goes up to week 6 (11 February 2024). Data for the most recent weeks may change, as further notifications are received and processed. Most data is therefore represented by a dotted line between weeks 5 and 6 of 2024.

Rates of scarlet fever notifications varied between regions, with the North West region reporting the highest rate (36.9 per 100,000) and the East of England the lowest (17.1 per 100,000) (see Table 1). The rate in the North West is followed by 36.0 per 100,000 in the East Midlands and 29.5 per 100,000 in the North East.

Table 1. Number and rate per 100,000 population of scarlet fever and iGAS notifications in England: 2023 to 2024 season

Region	Number of cases of scarlet fever	Rate of scarlet fever	Number of cases of iGAS	Rate of iGAS
East of England	1,133	17.1	108	1.6
East Midlands	1,757	36.0	111	2.3
London	1,668	19.0	149	1.7
North East	780	29.5	94	3.6
North West	2,740	36.9	181	2.4
South East	1,937	21.5	193	2.1
South West	1,134	19.9	126	2.2
West Midlands	1,235	20.7	150	2.5
Yorkshire and the Humber	1,365	24.9	167	3.0
England	13,749	24.3	1,279	2.3

Invasive group A streptococcal infection

Laboratory notifications of iGAS infection this season (weeks 37 to 6) are higher than usually seen by this point in the season (see Figure 2). There have been 1,243 cases reported so far this season, 433 recorded during 2024. This total is considerably below the total for the same period in the 2022 to 2023 season when 2,046 cases were reported – higher than the average (584), and the range (300 to 855), seen for the same period in the prior 5 seasons (2017/2018 to 2021/2022).

The highest rates this season were reported in the North East region (3.6 per 100,000 population), followed by the Yorkshire and Humber region (3.0 per 100,000), and the West Midlands region (2.5 per 100,000) (see Table 1).

Figure 2. Weekly laboratory notifications of iGAS, England, by season, 2017 to 2018 onwards

Note: in this graph, notifications for the most recent weeks of the 2023 to 2024 season are expected to increase due to lags in reporting timelines from laboratories. The decline in notifications shown for recent weeks should therefore be interpreted with caution and is represented here by a dashed line between weeks 4 and 6.

The median age of patients with iGAS infection so far this season is 57 years (range 1 year and under to 99 years) in line with the range seen at this point in the preceding 6 seasons (51 to 59 years). Rates of iGAS infection were highest for the 75 years and older age group (7.0 per 100,000), followed by under 1 year olds (5.4 per 100,000) and 65 to 74 year olds (3.0 per 100,000). The patterns in rates for different age groups are similar to what has been observed in previous seasons and are not the same as the unusual pattern noted in children during the 2022 to 2023 season.

Antimicrobial susceptibility results obtained from routine laboratory surveillance of iGAS isolates this season (weeks 37 to 6) were broadly consistent with prior years, and below the high level of antimicrobial resistance described in 2021 (2), in particular:

• isolates were reported as universally (100%) susceptible to penicillin
• 6% were resistant to clindamycin (compared with 4% last season; range 4% to 21% in the last 5 years)
• 9% were resistant to erythromycin (compared with 4% last season; range 4% to 21% in the last 5 years)
• 26% were resistant to tetracycline (compared with 13% last season; range 13% to 45% in the last 5 years)

Analysis of reference laboratory iGAS isolate submissions indicates a diverse range of emm gene sequence types identified so far this season. The results indicate that emm1.0 remains the most common (16.6% of referrals), followed by emm3.93 (11.9%), emm28.0 (5.6%), emm89.0 (5.5%) and emm4.0 (5.1%)

During the same period of the 2022 to 2023 season, emm1.0 was the most frequently identified (49%), followed by emm12.0 (12%) followed by emm89.0 (4%) .

Discussion

After a period of elevated notification during last winter, scarlet fever notifications throughout 2023 reduced to levels at the top end of what would normally be reported at this point in the season. GP consultations for scarlet fever also suggest elevated levels in early 2024 (3). Excluding the exceptionally high winter peak recorded for scarlet fever during the 2022 to 2023 season, notifications during the current season are higher than in previous seasons, possibly reflecting in part heightened awareness and improved diagnosis and/or notification practices.

As with scarlet fever, the rate of iGAS infection in the early part of the current season has followed a normal seasonal pattern, albeit at the higher end of the range than would normally be expected. Incidence remains significantly below the exceptional levels being recorded this time last year, with laboratory notifications and age group distribution being within the range normally expected.

This season, a clonal expansion has been observed in the emm3.93 subtype; with a previous expansion on this subtype seen in the 2017 to 2018 season. Early investigations show that antimicrobial resistance in the emm3.93 iGAS cases is low, at less than 2% resistance for each of tetracycline, erythromycin and clindamycin. Detailed genomic and biological investigations are under way to investigate this emergence.

Reduced exposure to GAS infections during the pandemic was likely to have increased the population’s susceptibility to these infections last season. 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 (3, 4). 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
• Scarlet fever: symptoms, diagnosis and treatment (factsheet)
• UK guidelines for the management of contacts of invasive GAS infection in community cases
• Guidelines for prevention and control of group A streptococcal infection in acute healthcare and maternity settings in the UK
• Weekly notifiable disease reports (NOIDS)
• Group A strep – what you need to know (blog)

All invasive disease GAS isolates – and 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 notification data was extracted from the notifications of infectious diseases (NOIDs) reports. Data for England was extracted on 20 February 2024. Weekly totals include a few scarlet fever notifications identified in port health authorities; this will mean that the regional totals will not equal the season total for England.

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 20 February 2024.

The sharp increase in scarlet fever and other group A streptococcal infections, alongside increased awareness and vigilance amongst clinicians, led to a significant rise in scarlet fever notifications during winter 2022. This resulted in a backlog of notifications of scarlet fever cases being entered into the national database after being processed. As a result, notifications for the 2022 to 2023 season are still being finalised and numbers presented here may change in future reports.

The GAS surveillance season runs from week 37 in one year to week 36 in the following year (mid-September to mid-September). The 2023 to 2024 season data in this report covers the period 11 September 2023 to 11 February 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.

Prior to the COVID-19 pandemic, there were a number of seasons with elevated incidence of scarlet fever and iGAS, 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. Guy R, Henderson KL, Coelho J, Hughes H, Mason EL, Gerver SM, and others. Increase in invasive group A streptococcal infection notifications, England, 2022 Eurosurveillance 2023: volume 28, number 1

2. UKHSA (2018), GP in-hours consultations bulletin: 15 February 2024, week 6

3. UKHSA (2022). English surveillance programme for antimicrobial utilisation and resistance (ESPAUR): report 2021 to 2022

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

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

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.

The support from colleagues within UKHSA, and the AMRHAI Reference Unit in particular, is valued in the preparation of the report.

Feedback and specific queries about this report are welcome via [email protected]