Main points

Scarlet fever activity for the current 2024 to 2025 group A streptococcal (GAS) season is in line with normal seasonal patterns, with GP consultations increasing in the first three weeks of 2025. Laboratory notifications of invasive group A streptococcal (iGAS) infection are also within normal levels for the time of year.

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 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.

Numbers presented in this seasonal activity update are based on data available as of 21 January 2025 for diagnoses up to and including 19 January 2025 (end of week 3). Numbers presented may change as updated data becomes available.

Key definitions are available at the end of the report.

Scarlet fever

GP in-hours consultations for scarlet fever for the first three weeks of 2025 have seen an increase, in line with normal seasonal patterns, reaching 0.80 per 100,000 population in week 3.

So far this season (week 37 2024 to week 3 2025), the highest weekly rate of in-hours GP consultations was in week 52 of 2024 at 1.07 per 100,000 population. The rate for the latest week (week 3 2025) falls within the range (0.06 to 3.03) observed for the same week in the last six seasons (2018/19 season to 2023/24 season).

Figure 1. Weekly scarlet fever GP in-hours consultation rate in England, by season, 2018 to 2019 season onwards

Note: Data shown for the current season goes up to week 3 (19 January 2025).

Invasive group A streptococcal infection

Laboratory notifications of iGAS infection in the first 6 weeks of the 2024/25 season (weeks 37 2024 up to week 3 2025) are comparable to those typically seen at this time of year (Figure 2). A total of 811 notifications of iGAS disease have been received, with a weekly high of 53 notifications in week 1 (30 December 2024 to 5 January 2025). Cumulative numbers of iGAS infections so far this season are higher than average (662) but within range (295 to 1030) for the same period in the prior 5 seasons (2018 to 2019 to 2023 to 2024 seasons, excluding the 2022/23 upsurge season).

So far this season, the highest notification rates were in London and the North East (2.3 per 100,000 population), followed by Yorkshire and the Humber (1.9), and the West Midlands (1.7).

Figure 2. Weekly laboratory notifications of iGAS, England, by season, 2018/19 season onwards

Note: Numbers of notifications in the latest weeks of the 2024/25 season are expected to increase due to a lag in laboratory reporting. The decline in notifications in recent weeks should be interpreted with caution; delayed processing and reporting timeframes are represented by a dashed line between weeks 2 and 3 of 2025.

Rates of iGAS infection to date this season were highest in those aged 75 years and older (5.0 per 100,000), followed by those under 1 year (2.6), and 65 to 74 year-olds (1.7). The lowest notification rate was observed in 10 to 14 year-olds, 0.4 per 100,000. Early seasonal rates for different age groups are broadly consistent with past seasons, except for the unusual pattern noted among children in the 2022/23 season (1).

The median age of notified cases of iGAS infection so far this season is 59 years (range of 0 to 101 years). This is slightly higher than the median age ranges reported for this point in the preceding six seasons (49 to 57 years).

Antimicrobial susceptibility results obtained from routine laboratory surveillance for iGAS infection so far (week 37 2024 to 3 2025) were within the normal range seen at this point in the season , although at the higher end for erythromycin and tetracycline resistance. Specifically:

• isolates were reported as universally (100%) susceptible to penicillin
• 9% were resistant to clindamycin (6% in 2023/24; range 4% to 15% in the last 6 seasons)
• 19% were resistant to erythromycin (9% in 2023/24; range 4% to 20% in last 6 seasons)
• 41% were resistant to tetracycline (27% in 2023/24; range 12% to 44% in the last 6 seasons)

Analysis of reference laboratory iGAS isolate submissions indicated a diverse range of emm gene sequence types identified to date this season (week 37 2024 to week 2 2025), with emm 49.8 the most common type (11.1% of all referrals), followed by emm 89.0 (5.3%) and emm 8.0 (5.1%).

Discussion

Following the 2022/23 season, which saw a period of considerable elevation in scarlet fever notifications (1, 2) and unusual seasonal patterns, the 2023/24 season saw a return to more usual GAS activity. At this point in the 2024/25 season, scarlet fever rates are in line with expected levels, with increases in consultation rates being noted in the first 3 weeks of 2025 as is typical for this time of year.

Similarly, cases of iGAS infection this season are following expected patterns and levels of activity. Incidence remains below the high levels recorded in the 2022/23 season, and the total to date in the 2024/25 season is currently below the level seen in the previous two seasons. The pattern of weekly laboratory notifications and age group distribution are within the range typically expected.

So far this season emm 49.8 is emerging as the most common gene type, a change from a similar point in the previous season when emm 3.93 emerged as the dominant emm type (3). Early investigations show that emm 49.8 isolates have a higher frequency of resistance to tetracycline and erythromycin (>90%), with clindamycin resistance lower at 15%. This differs from emm 3.93 isolates, where low level of resistance to these antibiotics was found (<2% resistant) (4). GAS remains universally susceptible to penicillin which remains the drug of choice. Detailed genomic 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 (5, 6). 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
• 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
• Report a Notifiable Disease (eNOIDS)
• weekly notifiable disease reports
• 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:

Data sources and methods

Scarlet fever data is presented as GP in-hours consultation rates per 100,000 registered population. This information is 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 (7).

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 21 January 2025.

A season runs from week 37 in one year to week 36 in the following year (mid-September to mid-September). The 2024/25 season data within this report covers 9 September 2024 to 14 January 2025.

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. Information for the emm gene was extracted from UKHSA’s reference laboratory and this report contains data covering the period 9 September 2024 to 14 January 2025.

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 2017/18 season. During the 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, 2022/23

2. 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

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

4. UKHSA (2024). Group A streptococcal infections: fifth update on seasonal activity in England, 2023/24

5. 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

6. 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

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

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