Research and analysis

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

Updated 4 April 2024

Applies to England

In the first 22 weeks of the 2023/24 season (week 37 to week 12), scarlet fever notifications followed a typical seasonal pattern, although numbers of notifications were at the higher end of what is normally expected. Notifications showed a moderate December peak followed by a decline after week 51, with a typical seasonal rise up to week 6. Scarlet fever notifications have fluctuated in recent weeks and 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, with numbers of cases 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 2022/23 season when high rates of iGAS infection in children were observed in the early part of the season (1). This season there has also been a change in the circulating iGAS strain types, moving away from the unusual dominance of emm1.0 that was seen last season; while emm 1.0 is still prevalent this season, a wider variety of other strain types is now being seen.

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, 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 26 March 2024 and covers notifications up to 24 March 2024 (the end of week 12). 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

Scarlet fever notifications remain high but within the range of what is normally expected for the time of year. Weekly notification totals are similar to those observed during the 2022/23 season and below those of the 2017/18 season. Notifications peaked in week 51 of 2023, with 1,021 notifications, and then again in week 6 of 2024, with 1,394 notifications, after which there has been some fluctuation: a slight decline followed by an increase in more recent weeks. Another increase is being seen in the most recent weeks, in line with expected seasonal patterns, with 1,165 notifications recorded so far for week 12 (Figure 1).

A total of 19,528 notifications have been made so far in the current season, of which 12,176 were in the 2024. This is outside the range of weekly notification totals (819 to 17,454) – and higher than the average (8,475) – seen in the previous 5 seasons (2017/18 to 2021/22).

Scarlet fever notifications for the 2022/23 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 season onwards

Note: Data shown for the current season goes up to week 12 (24 March 2024); because data for the most recent weeks may change, as further notifications are received and processed, that data is represented by a dotted line between weeks 11 and 12 of 2024.

Cumulative rates of scarlet fever notifications this season have varied between regions, with the East Midlands region reporting the highest rate of 53.5 per 100,000 and the South West the lowest (24.2 per 100,000). The North West (49.0) and North East (45.1) had the next highest rates.

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	1,702	25.6	134	2.0
East Midlands	2,610	53.5	138	2.8
London	2,537	28.8	188	2.1
North East	1,193	45.1	122	4.6
North West	3,638	49.0	233	3.1
South East	3,147	34.9	229	2.5
South West	1,382	24.2	163	2.9
West Midlands	1,715	28.8	194	3.3
Yorkshire and the Humber	1,604	29.3	224	4.1
England	19,528	34.5	1,625	2.9

Invasive group A streptococcal infection

Laboratory notifications of iGAS infection so far this season (weeks 37 to 12, 2023/24) are similar to what is usually seen at this time of year (Figure 2). So far this season there have been 1,625 cases reported, of which 817 were in 2024. The seasonal total to date is considerably below the total observed for the same period in the previous 2022/23 season which saw 2,713 cases reported. Notifications made so far this season (1,625) are outside the range (465 to 1,565; average 1,066) seen for the same period in the prior 5 seasons (2017/18 to 2021/22).

The highest rates this season were reported in the North East region (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 2023/24 season are expected to increase due to lags in reporting timelines from laboratories. The decline in recent weeks should be interpreted with caution and is represented here by a dashed line between weeks 11 and 12 of 2024.

Of reports received this season to date, rates were highest in those aged 75 years and older (8.8 per 100,000), followed by those under 1 year old (6.4 per 100,000), and 65 to 74 year olds (4.0 per 100,000). The lowest rate of infection was observed in 10 to 14 year olds (1.1 per 100,000). The rate in the 75 years and older age group is considerably higher in the current season than the rate observed in previous 5 seasons (2017/18 to 2021/22) which have a range of 1.5 to 3.9. The patterns in rates for different age groups are not the same as the unusual pattern noted in children in 2022/23.

The median age of patients with iGAS infection so far this season is 56 years, with a range of 0 to 99 years; this is 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 6) were broadly consistent with prior years, and below the elevated levels 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 16% in the last 5 years)
• 9% were resistant to erythromycin (4% last season; range 4% to 21% in the last 5 years)
• 25% were resistant to tetracycline (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 emm3.93 is now the most common gene type (14.1% of referrals), followed by emm1.0 (13.0% of referrals). Gene types emm89.0 and emm28.0 are the next most commonly isolated (5.0% and 4.9% of referrals, respectively). During the same period of the 2022/23 season, emm1.0 was the most frequently identified (54%), followed by emm12.0 (11%) and emm89.0 (4%) .

Discussion

After a period of elevated notification during last winter, scarlet fever notifications throughout 2023 stayed at the top end of normal seasonal levels. GP consultations for scarlet fever have been following a similar pattern so far this year and, in recent weeks, demonstrate an increasing trend (3). The levels of weekly notification in the current season are following a normal seasonal pattern, with a slight December elevation followed by a slightly larger February/March increase. Notifications for recent weeks are comparable to the number of notifications reported in the 2022/23 season, and lower than the 2017/18 season.

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 below the high levels 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 2017/18 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, epidemiological, and biological investigations are under way to investigate this emergence.

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
• 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 26 March 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 26 March 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 2022/23 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 2023/24 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 2017/18 season.

During the COVID-19 pandemic, there there was an unprecedented reduction in the number of scarlet fever and iGAS notifications, affecting the 2019/20 season and the 2021/22 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. UKHSA (2022). English surveillance programme for antimicrobial utilisation and resistance (ESPAUR): report 2021 to 2022

3. UKHSA (2024), GP in-hours consultations bulletin: 28 March 2024, week 12

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

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 hcai.amrdepartment@ukhsa.gov.uk