Research and analysis

Group A streptococcal infections: 13th update on seasonal activity in England

Updated 29 June 2023

Applies to England

Data to 16 April 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 remained above usual seasonal levels; they are now within the range normally expected at this point in the season.

Notifications of invasive group A streptococcus (iGAS) disease remain slightly above what is normally seen at this time of year. Relatively high rates of iGAS infection in children have been observed with increases in adults occurring in recent weeks.

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 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 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.

Data presented within this seasonal activity update is based on data available as of 19 April 2023 and present data to 16 April 2023 (the end of week 15). 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 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 54,394 notifications of scarlet fever were received from week 37 to week 15 of this season (2022 to 2023) in England, with a pre-Christmas peak of 10,068 notifications in week 49. This compares with an average of 9,961 (range 907 to 21,544) for this same period (weeks 37 to 15) 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 lower than those reported in December 2022, and in recent weeks have declined to levels seen at this point last season. There have been 17,981 scarlet fever notifications in the first 15 weeks of 2023, higher than the average for this point in the calendar year (5,612, range 428 to 17,352) between 2018 and 2022.

Figure 1. Weekly scarlet fever notifications in England, by season, 2017 to 2018 onwards (weeks 37 to 15)

Note: Data for the current season goes up to week 15 (16 April 2023); data for the most recent weeks may change as further notifications are received and processed, represented by a dotted line between weeks 13 and 15.

Scarlet fever notifications to date this season showed considerable variation across England, ranging between 76.6 (West Midlands) and 137.5 (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 15 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 15 covers the period 12 September 2022 to 16 April 2023.

Region	Number of cases of scarlet fever	Rate of scarlet fever	Number of cases of iGAS	Rate of iGAS
East of England	5,464	82.3	289	4.4
East Midlands	6,710	137.5	295	6.0
London	7,175	81.6	341	3.9
North East	2,232	84.3	173	6.5
North West	8,934	120.4	369	5.0
South East	7,915	87.9	516	5.7
South West	5,189	90.8	308	5.4
West Midlands	4,560	76.6	295	5.0
Yorkshire and the Humber	6,208	113.3	379	6.9
England	54,394	96.2	2,965	5.2

Invasive group A streptococcal infection

Laboratory notifications of iGAS infection so far this season (weeks 37 to 15, 2022 to 2023) remain considerably higher than expected (Figure 2). A total of 2,965 notifications of iGAS disease were reported through laboratory surveillance in England, higher than recorded over the last 5 seasons for the same weeks (average 1,221, range 517 to 1,867 notifications Figure 2), with a weekly high of 213 notifications in week 52 (26 December 2022 to 1 January 2023).

There have been 1,555 iGAS laboratory notifications in the first 15 weeks of 2023, higher than the average for this point in the calendar year (725; range 260 to 1,270 between 2018 and 2022).

Whilst laboratory notifications remain lower than the high recorded in week 52, levels of iGAS activity remain slightly above what would be expected at this point in the season. Further increases are possible in the coming few weeks as we move towards the usual time of year for peak activity, typically occurring between weeks 6 and 18.

Figure 2. Weekly laboratory notifications of invasive GAS, England, by season, 2017 to 2018 onwards (weeks 37 to 15)

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 mean that increases in laboratory reports are expected – represented by a dashed line between weeks 13 and 15. More details of the improved processing method implemented since the 10th update report are described in the data and methods section of this report.

During the current season to date, the highest rates were reported in the Yorkshire and Humber region (6.9 per 100,000 population), followed by the North East (6.5 per 100,000) and East Midlands regions (6.0 per 100,000); see Table 1.

The highest rate was in the group of those aged 75 years and over (12.4 per 100,000) followed by the group of those aged 1 to 4 years (12.1 per 100,000) and group of those aged under one year (10.2 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 12 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 15, 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 15): number of cases	2022 to 2023 season (weeks 37 to 15): 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	75	12.9	78	12.2
1 to 4	328	13.2	194	7.1
5 to 9	206	6.2	112	3.2
10 to 14	73	2.1	37	1.1
15 to 44	555	2.6	622	2.9
45 to 64	604	4.1	613	4.3
65 to 74	418	7.5	468	8.4
75 and over	699	14.3	773	16.7
Total	2,965	5.2	2,898	5.2

The median age of patients with iGAS infection so far this season was 55 years (range under 1 year to 105 years) and, for the calendar year so far, 57 years (range under 1 year to 105 years) in the first 15 weeks of 2023; see Table 2.

Twenty one per cent of iGAS infections reported so far this season are in children (aged 15 years and under), higher than the range seen at this point for the past 5 seasons (4% to 18%).

So far this season 401 deaths (from any cause) have been recorded within 7 days of an iGAS infection diagnosis (176 occurring in 2023), with 64% (n=257) of the recorded deaths being in those aged 65 years and over, and 9% (n=38) in children aged 10 years and under (Table 3). The all-cause case fatality rate (CFR) to date is higher than in recent seasons, although it does vary by age group with the CFR being more elevated in elderly people. 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 45 deaths in children aged under 15 years identified to date for weeks 37 to 15.

There have been 701 iGAS reports in children under 18 years in the season to date (24% of iGAS reports), with 47 deaths being recorded in this age group (CFR of 7.1%).

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 (37%). Susceptibility testing of iGAS isolates against erythromycin indicated 4% were found resistant (compared with 13% last season), and, for clindamycin, 4% were resistant at this point in the season (12% 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 (54% of referrals), followed by emm 12.0 (11%) and emm 89.0 (4%), compared with 24%, 6% and 10% at the same point in the 2017 to 2018 season, respectively. In children (aged under 15 years) emm 1.0 and emm 12.0 have dominated this season, accounting for 66% and 15% respectively (compared with 29% and 8% 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

Note: 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 15 (12 September 2022 to 16 April 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 15) % 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%	8.2%	6
1 to 4	4.7%	6.1%	9.0%	5.9%	6.2%	18
5 to 9	9.9%	4.6%	2.7%	10.6%	6.6%	13
10 to 14	7.9%	8.7%	23.8%	0.0%	10.8%	7
15 to 44	4.1%	1.7%	2.5%	2.3%	6.5%	34
45 to 64	8.4%	8.6%	9.3%	9.7%	11.1%	65
65 to 74	13.5%	8.8%	13.8%	13.1%	15.9%	63
75 and over	24.4%	16.8%	19.9%	18.1%	28.8%	194
Total	12.4%	9.1%	11.3%	10.0%	14.2%	401

Discussion

After a period of elevated notification, scarlet fever notifications in recent weeks have fallen to levels 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 notifications in week 49, and also reducing onward transmission due to increased case ascertainment. Routine monitoring will continue over the coming weeks to identify potential increases in line with the normal seasonal pattern.

The rate of iGAS infection notifications across the season also showed a pattern of elevation, with weekly incidence trending considerably above what would be expected during the first part of the season, particularly during December 2022 but continuing into early 2023.

Investigations are continuing following reports of an increase in lower respiratory tract GAS infections, particularly empyema, in children during November and December 2022 (1). The current emm types have been circulating for many years. While a newer strain of emm1 (M1UK) was documented as having emerged and expanded in the last decade, its role (if any) in driving the current high levels of iGAS in children remains uncertain. Detailed genomic and biological investigations are under way to investigate any differences in the pathogen being seen this season.

The elevated iGAS levels in children compared to the period when pandemic control measures were in place is likely to be a consequence of the heightened scarlet fever activity given the crossover of strains associated in both presentations (2, 3). Reduced exposure to GAS infections during the pandemic is also likely to have led to increased susceptibility to these infections in children, in view of the very low levels seen during the pandemic. Prompt treatment of scarlet fever with antibiotics is recommended to reduce risk of possible complications and limit onward transmission.

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 (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 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 18 April 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 19 April 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 16 April 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 2 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 is to be 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 coronavirus (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. Chalker V, Jironkin A, Coelho J, Al-Shahib A, Platt S, Kapatai G, and others (2017). ‘Genome analysis following a national increase in scarlet fever in England 2014’. BMC Genomics: volume 18 number 1, page 224

3. Al-Shahib A, Underwood A, Afshar B, Turner CE, Lamagni T, Sriskandan S, and others (2016). Emergence of a novel lineage containing a prophage in emm/M3 group A Streptococcus associated with upsurge in invasive disease in the UK’. mGen; volume 2 number 11

4. 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

5. 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 [email protected]