Research and analysis

Group A streptococcal infections: 15th update on seasonal activity in England

Updated 29 June 2023

Applies to England

Data to 18 June 2023.

Main points

Notifications and GP consultations of scarlet fever in England identified exceptionally high levels of activity in the early phase of the 2022 to 2023 season. While rapid declines were seen in the second half of December, numbers of scarlet fever notifications are now fluctuating within normal seasonal levels.

After the high levels of notifications of invasive group A streptococcus (iGAS) disease seen during December, incidence has been fluctuating at the upper end of the range expected for the time of year. Relatively high rates of iGAS infection in children were observed earlier in the season (1), with the age distribution of iGAS cases returning to a more usual pattern since February 2023.

Medical practitioners were alerted to this early increase in incidence and elevated iGAS infection in children on 2 December 2022. 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 people who are 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 and updated on 2 March 2023, with public health action extended to include patients with probable invasive GAS infection and additional close contact groups now 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 or work until 24 hours of antibiotic treatment has been received.

This seasonal activity update is based on data available as of 27 June 2023 and presents data to 18 June 2023 (the end of week 24). Numbers presented in this report may change when 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

Higher than expected scarlet fever activity was noted during the early part of summer 2022 in England. Notifications during the early part of the current season (2022 to 2023) increased to exceptional levels (Figure 1). (Seasons are defined as running from week 37 (mid-September) in one year to week 36 in the following year.)

A total of 58,972 notifications of scarlet fever were received from week 37 to week 24 of this season (2022 to 2023) in England, with a pre-Christmas peak of 10,069 notifications in week 49. This compares with an average of 12,906 (range 1,296 to 28,303) for this same period (weeks 37 to 24) in the previous 5 years. Increased health seeking behaviour as a result of national alerts is likely to have contributed to the increased reports. The last peak season for scarlet fever notifications was 2017 to 2018 when 30,768 reports were received across the entire season.

Notifications in the early weeks of 2023 remain considerably lower than those reported in December 2022 and within the range seen in the past 5 years since week 8 of 2023.

Figure 1. Weekly scarlet fever notifications in England, by season, 2017 to 2018 onwards (weeks 37 to 24)

Note: Data for the current season goes up to week 24 (18 June 2023); data for the most recent weeks may change as further notifications are received and processed, represented by a dotted line between weeks 23 and 24.

Scarlet fever notifications to date this season showed considerable variation across England, ranging between 82.7 (West Midlands) and 146.1 (East Midlands) 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 to week 24 of the 2022 to 2023 season

Notes: More details of an improved processing method implemented since the 10th update report are described in the data and methods section of this report. Week 37 to week 24 covers the period 12 September 2022 to 18 June 2023.

Region	Number of cases of scarlet fever	Rate of scarlet fever	Number of cases of iGAS	Rate of iGAS
East of England	5,848	88.1	364	5.5
East Midlands	7,132	146.1	343	7.0
London	7,802	88.7	434	4.9
North East	2,408	91.0	219	8.3
North West	9,657	130.1	468	6.3
South East	8,547	94.9	655	7.3
South West	5,367	93.9	397	6.9
West Midlands	4,924	82.7	372	6.2
Yorkshire and the Humber	7,287	132.9	477	8.7
England	58,972	104.3	3,729	6.6

Invasive group A streptococcal infection

Laboratory notifications of iGAS infection so far this season (weeks 37 to 24, 2022 to 2023) remain slightly higher than expected (Figure 2). A total of 3,729 notifications of iGAS disease were reported through laboratory surveillance in England, with a weekly high of 213 notifications in week 52 (26 December 2022 to 1 January 2023).

Laboratory notification of iGAS infection for the season so far (weeks 37 to 24) are higher than recorded over the last 5 seasons for the same weeks (average 1,591; range 677 to 2,484 notifications Figure 2).

There have been 2,316 iGAS laboratory notifications in the first 24 weeks of 2023, higher than the average for this point in the calendar year between 2018 and 2022 (1,095; range 420 to 1,887).

While laboratory notifications remain lower than the exceptionally high numbers recorded at the end of 2022, levels of activity remain above what would be expected at this point in the season.

During the current season to date, the highest rates were reported in the Yorkshire and Humber region (8.7 per 100,000 population), followed by the North East (8.3 per 100,000) and East Midlands (7.0 per 100,000); see Table 1.

Figure 2. Weekly laboratory notifications of invasive GAS, England, by season, 2017 to 2018 onwards (weeks 37 to 24)

Notes: In this graph, the most recent weeks of the 2022 to 2023 season are expected to increase due to lags in reporting timelines from laboratories. The decline in recent weeks should be interpreted with caution; normal processing and reporting timeframes, in addition to bank holidays, mean that increases in laboratory reports are expected – represented by a dashed line between weeks 23 and 24. More details of the improved processing method implemented since the 10th update report are described in the data and methods section of this report.

The highest rate was in the group of those aged 75 years and over (16.2 per 100,000) followed by those aged under 1 year (15.2 per 100,000) and those aged 1 to 4 years (14.2 per 100,000); see Table 2.

Table 2. Rate per 100,000 population of iGAS notifications in England by age group, week 37 to week 24 in the 2022 to 2023 season versus the 2017 to 2018 season

Note: In this table the current 2022 to 2023 season covers weeks 37 to 24, whereas the 2017 to 2018 season data covers the full season, weeks 37 to 36. More details on an improved processing method implemented since the 10th update report are described in the data and methods section of this report.

Age group (years)	2022 to 2023 season (weeks 37 to 24): number of cases	2022 to 2023 season (weeks 37 to 24): rate per 100,000 population	2017 to 2018 (full season): number of cases	2017 to 2018 (full season): rate per 100,000 population
Aged 1 year and under	97	16.7	78	12.2
1 to 4	388	15.7	194	7.1
5 to 9	244	7.3	112	3.2
10 to 14	78	2.3	37	1.1
15 to 44	676	3.1	622	2.9
45 to 64	777	5.3	613	4.3
65 to 74	536	9.6	468	8.4
75 and over	993	19.0	773	16.7
Total	3,729	6.6	2,898	5.2

The median age of patients with iGAS infection so far this season, and for the calendar year so far, was 55 years (range under 1 year to 105 years).

So far this season 491 deaths (from any cause) have been recorded within 7 days of an iGAS infection diagnosis, with 64% (n=316) of the recorded deaths being in those aged 65 years and over, and 9% (n=45) in children aged 10 years and under (Table 3).

The all-cause case fatality rate (CFR) to date is higher than in recent seasons, and CFRs are more elevated in elderly people – a likely reflection of the dominance of the emm 1 strain, which is associated with higher case fatality (2). Elevations in rates of iGAS infection in children in this early part of this season have resulted in an increased number of deaths over a relatively short period, with 52 deaths in children aged under 15 years identified to date for weeks 37 to 24.

There have been 834 iGAS reports in children under 18 years in the season to date (22% of iGAS reports), with 55 deaths being recorded in this age group (CFR of 7.0%).

Antimicrobial susceptibility results obtained from routine laboratory surveillance so far this season indicate tetracycline resistance in 12% of GAS sterile site isolates; this is lower than at this point last season (30%). Susceptibility testing of iGAS isolates against erythromycin indicated 5% were found resistant (compared with 12% last season), and, for clindamycin, 4% were resistant at this point in the season (11% last season). Isolates remained universally (100%) susceptible to penicillin.

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 (53% of referrals), followed by emm 12.0 (10%) and emm 89.0 (4%), compared with 24%, 6% and 9% at the same point in the peak season of 2017 to 2018 season, respectively. In children (aged up to 15 years) emm 1.0 and emm 12.0 have dominated this season, accounting for 65% and 14%, respectively (compared with 30% and 7% at this point in the 2017 to 2018 season).

Table 3. Case fatality rate (%) for deaths (all causes) within 7 days of an iGAS specimen, by age group in England for the current season and the previous 5 seasons

Notes: The total may include notifications where the age was unknown. The case fatality rate is the percentage of deaths within 7 days of iGAS infection diagnosis for cases where follow-up has been possible. CFR should be interpreted with caution given the small numbers involved. The current season data (2022 to 2023) covers week 37 to week 24 (12 September 2022 to 18 June 2023). The prior seasons cover the whole season (weeks 37 to 36). ‘Pandemic seasons’ presents data for the 2019 to 2020 and 2020 to 2021 seasons combined.

Age group (years)	2017 to 2018 season % CFR	2018 to 2019 season % CFR	Pandemic seasons (2019/2020 and 2020/2021) % CFR	2021 to 2022 season % CFR	2022 to 2023 season (weeks 37 to 24) % CFR	2022 to 2023 season: number of deaths (all causes) within 7 days of iGAS
Aged 1 year and under	5.6%	2.1%	7.7%	3.8%	9.5%	9
1 to 4	4.7%	6.1%	9.0%	5.9%	6.3%	23
5 to 9	9.9%	4.6%	2.7%	10.6%	5.6%	13
10 to 14	7.9%	8.7%	23.8%	0.0%	10.0%	7
15 to 44	4.1%	1.7%	2.5%	2.3%	6.3%	41
45 to 64	8.4%	8.6%	9.3%	9.7%	10.9%	82
65 to 74	13.5%	8.8%	13.8%	13.1%	15.5%	79
75 and over	24.4%	16.8%	19.9%	18.1%	26.0%	237
Total	12.4%	9.1%	11.3%	10.0%	13.7%	491

Discussion

After a period of elevated notification, scarlet fever notifications in recent months have fallen to levels normally reported at this point last season.

Public and healthcare professional alerts issued in week 48 (2 December 2022) may have succeeded in bringing people forward for clinical assessment and treatment, resulting in the sharp increase in scarlet fever notifications in week 49; other results will have been a reduction of onward transmission due to the effect of antibiotics in decreasing infectivity, and increased case ascertainment.

As for scarlet fever, the rate of iGAS infection notifications showed elevated incidence early in the season, reducing to levels trending slightly above what would be expected at this point in the season. The current emm types have been circulating for many years.

Reduced exposure to GAS infections during the pandemic is also likely to have led to increased susceptibility to these infections; it is noted that very low infection levels were recorded during the period where pandemic measures to limit social mixing were in place.

Public health messaging to encourage contact with NHS 111 or GP practices for clinical assessment of patients with specific symptoms suggestive of scarlet fever has been issued along with reminders to provide ‘safety netting’ advice for parents indicating signs and symptoms of deterioration, particularly for children with respiratory viral infection. 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 and elsewhere 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

• UK guidelines for the management of contacts of invasive group A streptococcus (iGAS) infections in community settings

• Prevention and control of group A streptococcal infection in acute healthcare and maternity settings

• Weekly notifiable disease reports are published for a timelier update

• Group A Strep – What you need to know (blog post)

All invasive disease GAS 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 22 June 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 27 June 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 in recent weeks. This has resulted in a backlog of notifications of scarlet fever cases being entered into the national database after being processed.

A season runs from week 37 in one year to week 36 in the following year (mid-September to mid-September). The 2022 to 2023 season data within this report covers 12 September 2022 to 7 May 2023.

All-cause deaths within +/- 7 days: reported date of death (obtained from tracing against the NHS SPINE where patient information is available) is compared to the date of iGAS specimen in a patient. This includes those where the difference between the two dates is ≤ 7 days, or ≥ minus 7 days (to include those potentially diagnosed via post mortem). Follow-up was not possible for all reported iGAS cases, primarily due to poor identifier (NHS number and date of birth) completion. In addition, not all iGAS cases have the full 7-day follow-up period for case fatality assessment. CFR should be interpreted with caution given the small numbers involved.

An improved method of patient iGAS episode de-duplication was implemented in the 10th update report and continued to be applied for all subsequent reports. The new method corrected an error which resulted in a small number of records being counted more than once in the iGAS episode analyses in the prior reports. This change does not impact the mortality data. The new method led to a 6% reduction in iGAS episodes recorded in the 2022 to 2023 season, impacting some regions more than others in the earlier seasonal update reports. Please refer to the appendix tables for a detailed comparison.

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 to 2018 season; this has been used as comparison point for the trends seen in the current 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, issue 1.

2. McManus O, and others (2023). Factors associated with mortality from invasive group A Streptococcus infection, England, 2015 to 2023. European Scientific Conference on Applied Infectious Disease Epidemiology (ESCAIDE) conference proceeding (abstract ID 577).

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.

Feedback and specific queries about this report are welcome via hcai.amrdepartment@ukhsa.gov.uk