Research and analysis

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

Updated 4 April 2024

Applies to England

Scarlet fever activity in England returned to normal seasonal levels from February 2023 and have continued so into the current 2023 to 2024 season.

The age distribution of invasive group A streptococcus (iGAS) cases returned to expected patterns from February 2023 onwards following the high rates of iGAS infection in children observed in the early part of the 2022 to 2023 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 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 close contacts of someone with scarlet fever.

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.

This first seasonal activity report is based on information available as of 25 October 2023 and presents data to 22 October 2023 (the end of week 42). 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 6 weeks of the current 2023 to 2024 season, weeks 37 and 42, scarlet fever notifications are showing normal levels of activity (Figure 1); seasons are defined from week 37 (mid-September) to week 36 (mid-September).

A total of 1,233 scarlet fever notifications were made so far this season, higher than average of 909 but within range (157 to 2,101) for this same period in the previous 6 years (2,101 for 2022 to 2023). This follows a season of exceptionally high activity with 61,442 notifications received from week 37 to 36 of the 2022 to 2023 season in England, with a pre-Christmas peak of 10,069 notifications in week 49.

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

Note: Data for the current season goes up to week 42 (22 October 2023); recent weeks in the current season may change as further notifications are received and processed, represented by a dotted line between weeks 41 and 42.

Scarlet fever notifications to date this season show considerable variation across England, ranging between 1.5 (East of England) and 3.6 (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 42 (22 October 2023) of the 2022 to 2023 season

Region	Number of cases of scarlet fever	Rate of scarlet fever	Number of cases of iGAS	Rate of iGAS
East of England	99	1.5	23	0.3
East Midlands	135	2.8	15	0.3
London	186	2.1	21	0.2
North East	57	2.2	17	0.6
North West	267	3.6	32	0.4
South East	154	1.7	22	0.2
South West	99	1.7	15	0.3
West Midlands	107	1.8	33	0.6
Yorkshire and the Humber	129	2.4	38	0.7
England	1,333	2.2	216	0.4

Invasive group A streptococcal infection

Laboratory notifications of iGAS infection so far this season (weeks 37 to 42, 2023 to 2024) were within the range normally seen at this time of year (Figure 2). A total of 216 notifications have been received, slightly higher than the average of 170 notifications for the same period over the last 6 seasons (range 85 to 279). This follows a season of exceptionally high iGAS notifications with a total of 4,412 iGAS episodes received in 2022 to 2023, peaking at 213 notifications in week 52 of 2022.

During the current season to date, the highest rates were reported in the Yorkshire and Humber region (0.7 per 100,000 population), followed by the North East and West Midlands regions (each 0.6 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 41 and 42.

So far this season, the highest rate of iGAS infection has been in the 75 years and over age group (1.4 per 100,000) followed by the 65 to 75 years (0.5 per 100,000). Across the entirety of last season, the highest rates were in the elderly (22.9 per 100,000 population in the 75 years and over age group), followed by the <1 year age group, with 18.3 per 100,000 population. The lowest rates were in the 10 to 14 year and 15 to 44 year age groups with 2.4 and 3.8 per 100,000 population respectively (overall rate for 2022 to 2023 was 7.8 per 100,000).

The median age of patients with iGAS infection so far this season was 59 years (range <1 year to 98 years), in line with the range seen at this point in the preceding 6 seasons (51 to 59 years). Five per cent of cases were in children aged less than 10 years (10 out of 216).

Antimicrobial susceptibility results obtained from routine laboratory surveillance of iGAS isolates this season (weeks 37 to 42) were broadly consistent with prior years, in particular:

• isolates were reported as universally (100%) susceptible to penicillin
• 7% were resistant to clindamycin (compared with 4% last season; range 4% to 45% in the last 5 years)
• 12% of isolates were resistant to erythromycin (compared to 4% last season; range 4% to 21% in the last 5 years), and
• tetracycline resistance was recorded in 26% of isolates (13% last season; range 13% to 45% in last 5 years)

Analysis of iGAS isolate typing data continues to indicate a diverse range of emm gene sequence types identified this season. The results indicate emm 1.0 remains the most common (16% of referrals), followed by emm 89.0, emm 28.0  and emm 108.1 (all 6%);  emm 108.1 has previously been associated with outbreaks in marginalised communities, such as the homeless and people who inject drugs (2).

Discussion

After a period of elevated notification during last winter, scarlet fever notifications throughout 2023 have fallen to within levels normally reported at this point in the season. As was the case with scarlet fever, the rate of iGAS infection notifications showed elevated incidence early in the last season, reducing to levels trending at the top end of what would be expected through the remainder of the season. The early part of the current season continues this trend, 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 24 October 2023. 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 25 October 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 in this first report on the 2023 to 2024 season 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 22 October 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, 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, 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, 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