Research and analysis

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

Updated 25 July 2024

Applies to England

Scarlet fever syndromic surveillance for the 2023/24 season is showing a general decline in GP consultations per 100,000 in recent weeks, in line with the normal seasonal pattern, although higher than average for the time of year. Laboratory notifications of invasive group A streptococcal (iGAS) infection in the current season are within normal levels for the time of year. Although the cumulative iGAS season total is slightly above average compared to the last 5 years, it remains substantially lower than the 2022/23 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, 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; and exclusion of cases from school and work until 24 hours of antibiotic treatment has been received.

Numbers presented in this seasonal activity update are based on data available as of 17 July 2024 for diagnoses up to and including 14 July 2024 (end of week 28). Numbers presented may change as updated data become available.

Key definitions are available at the end of the report.

Scarlet fever

Scarlet fever notifications in this report are based on GP in-hours syndromic surveillance data due to processing delays for scarlet fever notifications (2).

The current 2023/24 season has seen fluctuations in rates of in-hours GP consultations for scarlet fever in line with normal seasonal patterns, with peak activity observed in week 11, March 2024, reaching 3.88 per 100,000 population. This falls within the range (0.11 to 4.72) observed in the last 6 seasons although at the higher end, just below 2021/2022. A seasonal early-summer decline in scarlet fever consultations has been noted in recent weeks, although they remain slightly elevated for the time of year, notwithstanding the unusual activity seen in 2022/23.

Figure 1. Weekly scarlet fever notifications in England, by season, 2017 to 2018 season onwards (weeks 37 to 28)

Note, 2023/24 season goes up to week 28 (14 July 2024).

Invasive group A streptococcal infection

Laboratory notifications of iGAS infection in the latest weeks of the 2023/24 season (week 37 up to week 28) are comparable to those typically seen at this point in the season (Figure 2). To date there have been 2,631 iGAS notifications reported, considerably lower than the total observed for the same period last season (3,998; 2022/23 season). Invasive GAS notifications are higher than average (1,739) but within range (732 to 2,697) for the same period in the prior 5 seasons (2017/18 to 2021/22).

So far this season, the highest notification rates were in the North East region (7.5 per 100,000), followed by Yorkshire and Humber (6.5), and the North West (5.1).

Figure 2. Weekly laboratory notifications of iGAS, England, by season, 2017/18 season onwards

Note: Numbers of notifications in the latest weeks of the 2023/24 season are expected to increase due to lags in reporting timelines from laboratories. The decline in recent weeks – represented here by a dashed line between weeks 27 and 28 of 2024 – should therefore be interpreted with caution.

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 (3).

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)
• 24% 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 still the most common type (14.0% of referrals), followed by emm1.0 (all 8.3% of referrals); emm89.0 and emm28.0 are the next most commonly isolated (5.8% and 5.6% of referrals, respectively).

Discussion

A delay in processing scarlet fever notifications (2) has occurred this season necessitating the use of GP in-hours data for this report. Last season saw a period of considerable elevation in scarlet fever notifications (1)and unusual seasonal patterns, also seen in GP in-hours consultation rates (4). In comparison, this season so far has seen a return to more usual patterns, although slightly higher than average.

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 that 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 typically expected.

This season, a clonal expansion has been observed of an emm 3.93 subtype, with this now dominant, overtaking emm 1.0 (the dominant type from last season). A similar expansion has been reported in the Netherlands, and joint investigations found iGAS due to this type were associated with infections in children aged 6-17 years old in both countries, with no significant excess risk of death identified to date (5). Clinical presentations of pneumonia or pleural empyema were significantly associated with emm 3.93 for both countries, while in England emm 3.93 indicated increased risk for meningitis. Antimicrobial resistance in the emm 3.93 iGAS cases is low, at less than 2% resistance for each of tetracycline, erythromycin and clindamycin.

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 (6, 7). 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 data are presented as GP in hours consultations rates per 100,000 registered population – information 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 (8).

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 17 July 2024.

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

2. UKHSA (2024). Notifications of infectious diseases (NOIDs)

3. 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

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

5. Davies MA, de Gier B, Guy RL, Coelho J, van Dam AP, van Houdt R, and others.(2024), ‘Synchronous emergance of Streptococcus pyogenes emm type 3.93 with unique genomic inversion among invasive infections in the Netherlands and England’ (pre-print).

6. 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

7. 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

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

Acknowledgements

We thank TPP, ResearchOne and the SystmOne GP practices contributing to the UKHSA GP in hours syndromic surveillance system. Thanks also to the Oxford-Royal College of General Practitioners Clinical Informatics Digital Hub (ORCHID), and to its Syndromic Surveillance General Practices (SSGP) and their patients who share data with the UKHSA GP in hours syndromic surveillance system, and also to EMIS for facilitating pseudonymised data access.

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