Group A streptococcal infections: first update on seasonal activity in England, 2023 to 2024
Updated 4 April 2024
Applies to England
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In the first 12 weeks of the 2023 to 2024 season, scarlet fever levels are towards the higher end of what is normally expected at this time of year, though still well below the exceptionally high levels recorded for the previous 2022 to 2023 season.
Similarly, the incidence of invasive group A streptococcus (iGAS) disease has been slightly higher than what would normally be expected at this time of year. However, incidence remains well below what was observed this time last year. The age distribution of cases is following expected patterns, with the majority of cases in older age groups. This is unlike the previous 2022 to 2023 season where 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.
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.
Data presented within this seasonal activity update is based on information available as of 5 December 2023 and presents data to 3 December 2023 (the end of week 48). 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.
Scarlet fever
For the first 12 weeks of the current 2023 to 2024 season (weeks 37 to 48), scarlet fever notifications have been increasing in line with the seasonal pattern (Figure 1); seasons are defined from week 37 (mid-September) to week 36 (mid-September).
A total of 4,048 scarlet fever notifications were made so far this season, well below what was recorded last season (9,071 for 2022 to 2023) but higher than the average (1,774), or the range (333 to 2,915), for this same period in the prior 5 years (the 2017 to 2018 season to the 2021 to 2022 season).
Scarlet fever notifications for the 2022 to 2023 season remain provisional while the 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 (weeks 37 to 48)
Note: Data shown for the current season goes up to week 48 (3 December 2023); data for the most recent weeks may change, as further notifications are received and processed, and are therefore represented by a dotted line between weeks 47 and 48.
Scarlet fever notifications to date this season show considerable variation across England, ranging between 4.5 (East of England) and 11.6 (North West) per 100,000 population (Table 1).
Table 1. Number and rate per 100,000 population of scarlet fever and iGAS notifications in England: week 37 (11 September 2023) to week 48 (3 December 2023) of the 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 | 299 | 4.5 | 46 | 0.7 |
| East Midlands | 447 | 9.2 | 40 | 0.8 |
| London | 552 | 6.3 | 61 | 0.7 |
| North East | 210 | 7.9 | 39 | 1.5 |
| North West | 862 | 11.6 | 67 | 0.9 |
| South East | 567 | 6.3 | 61 | 0.7 |
| South West | 320 | 5.6 | 50 | 0.9 |
| West Midlands | 382 | 6.4 | 66 | 1.1 |
| Yorkshire and the Humber | 409 | 7.5 | 80 | 1.5 |
| England | 4,048 | 7.2 | 510 | 0.9 |
Invasive group A streptococcal infection
Laboratory notifications of iGAS infection so far this season (weeks 37 to 48, 2023 to 2024) are slightly higher than the range normally seen at this time of year (Figure 2). A total of 510 notifications have been received through laboratory surveillance in England to date this season. This total is well below the numbers recorded in the previous season (752 for 2022 to 2023); however notifications are higher than the average (326) or the range (184 to 465), seen for the same period in the prior 5 years (the 2017 to 2018 season to the 2021 to 2022 season).
During the current season to date, the highest rates were reported in the North East and in the Yorkshire and Humber regions (each 1.5 per 100,000 population), followed by the West Midlands region (1.1 per 100,000 population) (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 47 and 48.
During the current season to date, the highest rate of iGAS infection has been in the 75 years and over age group (3.1 per 100,000) followed by the less than 1 year age group (1.6 per 100,000). Eight per cent of cases were in children aged less than 10 years (43 out of 510) – a return to expected patterns, following the high rates of iGAS infection in children in the early part of the 2022 to 2023 season (1).
The median age of patients with iGAS infection so far this season has been 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).
Antimicrobial susceptibility results obtained from routine laboratory surveillance of iGAS isolates this season (weeks 37 to 48) were broadly consistent with prior years, in particular:
- isolates were reported as universally (100%) susceptible to penicillin
- 8% were resistant to clindamycin (4% last season; range 4% to 21% in the last 5 years)
- 13% were resistant to erythromycin (4% last season; range 4% to 21% in the last 5 years), and
- 34% were resistant to tetracycline (13% last season; range 13% to 45% in the last 5 years)
Analysis of iGAS isolate typing data continues to indicate a diverse range of emm gene sequence types identified so far this season. The results indicate emm 1.0 is the most commonly reported (17% of referrals), followed by emm 89.0 and emm 33.0 (each 7%). The emm types 66.0 and 108.1 have previously been associated with outbreaks in marginalised communities, such as the homeless and people who inject drugs (2); so far this season, 5% and 4% of all typed isolates were identified as emm 66.0 and 108.1, respectively.
Discussion
After a period of elevated notification during last winter, scarlet fever notifications throughout 2023 have fallen to levels at the top end of what would normally be reported at this point in the season.
Similar to scarlet fever, the rate of iGAS infection in the early part of the current season is following a normal seasonal pattern, albeit at the higher end of the range that would normally be expected. Incidence remains well below the exceptional levels being recorded this time last year, with laboratory notifications and age group distribution being within the range normally expected. The current emm types have been circulating for many years.
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 information can be found on GOV.UK:
- 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
- weekly notifiable disease reports
- 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 notification data was extracted from the notifications of infectious diseases (NOIDs) reports. Data for England was extracted on 7 December 2023. Weekly totals include a few scarlet fever notifications identified in port health authorities; this means 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 5 December 2023.
The sharp increase in scarlet fever and other group A strep infections alongside increased awareness and vigilance among clinicians has 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 subsequent updates.
A 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 within this report covers 11 September 2023 to 3 December 2023.
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 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. 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
2. Bundle N, Bubba L, Coelho J, Kwiatkowska R, Cloke R, King S, and others (2017). Ongoing outbreak of invasive and non-invasive disease due to group A Streptococcus (GAS) type emm66 among homeless and people who inject drugs in England and Wales, January to December 2016. Eurosurveillance: volume 22, number 3
3. Lamagni T, Guy R, Chand M, Henderson KL, Chalker V, Lewis J, and others (2018). ‘Resurgence of scarlet fever in England, 2014–16: a population based surveillance study’. The Lancet Infectious Diseases: volume 18, number 2, pages 180 to 187
4. 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, 2011–2016’. Emerging Infectious Diseases: 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 hcai.amrdepartment@ukhsa.gov.uk