Research and analysis

Group A streptococcal infections: eighth update on seasonal activity in England

Updated 29 June 2023

Applies to England

Data to 29 January 2023.

Main points

Notifications and GP consultations of scarlet fever in England have identified exceptional levels of activity during this early phase of the season. Whilst rapid declines were seen in the second half of December, numbers of notifications remained above usual seasonal levels and are now fluctuating, potentially indicating a reversal to increased activity. Notifications of invasive group A streptococcus (iGAS) disease also remain higher than expected for this time of year. Whilst relatively high rates of iGAS infection in children were seen at the start of the season, increases in adults have been noted in recent weeks. The elevated incidence of iGAS infection seen this season may reflect increases in respiratory viruses and high levels of GAS.

Medical practitioners were alerted to the 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 and maintain a high degree of clinical suspicion when assessing patients, particularly those with preceding viral infection (including chickenpox) or close contacts of scarlet fever.

Interim clinical guidance on management of GAS infection was issued to optimise diagnosis and treatment during this current increase in infection. Updated public health guidance on the management of close contacts of iGAS cases in community settings was published, with additional groups now recommended for antibiotic prophylaxis.

National guidance has highlighted the essential tools to limit spread: prompt notification of scarlet fever cases and outbreaks to UK Health Security Agency (UKHSA) Health Protection Teams (HPTs), 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 eighth seasonal activity update presents data to 29 January 2023 (the end of week 4). Numbers presented in this report may change when updated data becomes available. A seasonal update report will be published later in February. 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

Following higher than expected scarlet fever activity during the early part of this summer in England, notifications during the early part of the current 2022 to 2023 season – seasons extend from week 37 (mid-September) of one year to week 36 (mid-September) of the following year – increased to exceptional levels (Figure 1).

A total of 41,012 notifications of scarlet fever were received from week 37 to week 4 of this season in England, with a pre-Christmas peak of 10,009 notifications in week 49. This compares with an average of 3,909 (range 584 to 6,506) for this same period (weeks 37 to 4) in the previous 5 years (Figure 1). 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. However, they are still higher than in previous seasons for this time of year. The for this time of year. The rate of decline in notifications has slowed since week 52 with some fluctuation since week 2, potentially indicating a transition towards a period of increased activity.

Figure 1. Weekly scarlet fever notifications in England, by season, 2017 to 2018 onwards (weeks 37 to 4)

Note: Data in the figure for the current season goes up to week 4 (29 January 2023); data for the most recent weeks may change as further notifications are received and processed, represented by a dotted line between weeks 47 2022 and 4 2023.

Scarlet fever notifications to date this season showed considerable variation across England, ranging between 54.6 (West Midlands) and 109.9 (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 4 of the 2022 to 2023 season

Week 37 to week 4 covers the period 12 September 2022 to 29 January 2023.

Region	Number of cases of scarlet fever	Rate of scarlet fever	Number of cases of iGAS	Rate of iGAS
East of England	4,090	61.6	172	2.6
East Midlands	5,365	109.9	162	3.3
London	5,492	62.4	245	2.8
North East	1,697	64.1	109	4.1
North West	6,873	92.6	231	3.0
South East	6,141	68.2	334	3.7
South West	3,363	58.9	239	4.2
West Midlands	3,250	54.6	165	2.8
Yorkshire and the Humber	4,736	86.4	241	4.4
England	41,007	72.5	1,898	3.4

Invasive group A streptococcal infection

Laboratory notifications of iGAS infection so far this season (weeks 37 to 4, 2022 to 2023) showed levels considerably higher than expected (Figure 2). A total of 1,898 notifications of iGAS disease were reported through laboratory surveillance in England, with a weekly high of 226 notifications in week 52 (26 December 2022 to 1 January 2023). This is considerably higher than the last high season (2017 to 2018) where activity peaked at 113 cases in week 14 (2 April 2018 to 8 April 2018; (Figure 2). Laboratory notifications of iGAS infection this season are substantially higher than recorded over the last 5 seasons for the same weeks (average 639, range 308 to 945 notifications; Figure 2).

Figure 2. Weekly laboratory notifications of invasive GAS, England, by season, 2017 to 2018 onwards (weeks 37 to 4)

Note: 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 is expected – represented by a dotted line between week 2 and week 4.

Whilst a decline in weekly laboratory notifications has been seen since week 52, high levels of activity at such an early point in the season remain a concern, with further increases possible in the coming weeks as we move towards the usual time of year for peak activity, typically occurring between weeks 6 and 18

During the current season to date, the highest rates were reported in the Yorkshire and Humber region (4.4 per 100,000 population), followed by the South West (4.2 per 100,000) and North East (3.6 per 100,000; see Table 1.

The highest rate was in the 1 to 4 years age group (8.6 per 100,000), followed by those aged 75 years and over (8.2 per 100,000) and the under-1-year age group (5.9 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 4 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 4, whereas the 2017 to 2018 season data covers the full season, weeks 37 to 36. Of the cases recorded in the 2017 to 2018 season, 6 cases had unknown age-group but are included in the total for completeness.

Age group (years)	2022 to 2023 season (weeks 37 to 4): number of cases	2022 to 2023 season (weeks 37 to 4): 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	34	5.9	80	12.5
1 to 4	213	8.6	194	7.2
5 to 9	144	4.3	117	3.3
10 to 14	44	1.3	40	1.2
15 to 44	404	1.9	633	3.0
45 to 64	381	2.6	625	4.4
65 to 74	276	5.0	480	8.7
75 and over	402	8.2	792	17.0
Total	1,898	3.4	2,967	5.3

The median age of patients with iGAS infection so far this season was 50 years (range 1 year and under, to 102 years), lower than the range seen at this point in the preceding 5 seasons (age 54 to 59 years); 21% of iGAS infections reported so far this season are in children (aged 15 years and under), higher than the range seen for the past 5 seasons (5% to 13%). The slight increase in median age compared to earlier in the season, and the decreased percentage of iGAS that are in children (under 15 years of age), continued reflect the increases occurring in the older adult age groups (65 years and over).

So far this season 235 deaths have been recorded within 7 days of an iGAS infection diagnosis (from any cause), with 63% (n=149) of the recorded deaths being in those aged 65 years and over, and 10% (n=24) in children aged 10 years and under (Table 3). The overall case fatality rate (CFR) to date remains slightly higher than seen in recent seasons, although it does vary by age group with the CFR being more elevated in the elderly. 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 29 deaths in children aged under 15 in weeks 37 to 4.

There have been 423 iGAS reports in children under 18 years in the season to date (24% of iGAS reports), with 30 deaths being recorded in this age group (CFR of 7.5%). While this total is the same as published previously there has been 1 additional death within the 1 to 4 year age group with another from the 5 to 9 year age group being removed due to improved data cleaning processes (more information in the data sources and methods section).

Antimicrobial susceptibility results 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 (44%). Susceptibility testing of iGAS isolates against erythromycin indicated 4% were found resistant (compared with 19% last season) and, for clindamycin, 4% were resistant at this point in the season (15% last season). Isolates remained universally 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 was the most common (48% of referrals), followed by emm 12 (15%) and emm 89 (4%), compared with 20%, 7% and 11% at the same point in the 2017 to 2018 season respectively. In children (aged under 15 years) emm 1 and emm 12 have dominated this season, accounting for 58% and 23% respectively (compared with 20% and 10% 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 CFR 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 4 (12 September 2022 to 29 January 2023). The prior season’s data covers the whole season (weeks 37 to 36). ‘Pandemic seasons’ presents data for the 2019 to 2020 and 2020 to 2021 seasons combined. One death previously reported in the 5 to 9 age group for the 2022 to 2023 season has been reassigned to the 2021 to 2022 season due to an improved data cleaning methodology. More details on the improved processing are described in the data and methods section of the report.

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 2) % CFR	2022 to 2023 season: number of deaths (all causes) within 7 days of iGAS
Aged 1 year and under	5.7%	2.1%	7.7%	5.5%	5.9%	2
1 to 4	4.8%	6.1%	9.0%	5.9%	6.8%	13
5 to 9	10.0%	4.6%	2.7%	11.5%	7.1%	9
10 to 14	8.1%	8.7%	23.8%	0.0%	14.7%	5
15 to 44	4.2%	1.7%	2.5%	2.9%	6.1%	22
45 to 64	8.5%	8.9%	9.3%	9.7%	10.3%	35
65 to 74	13.5%	9.0%	13.8%	13.3%	18.3%	46
75 and over	24.8%	17.0%	19.9%	18.2%	29.1%	103
Total	12.5%	9.2%	11.4%	10.3%	13.9%	235

Discussion

While a recent downturn in scarlet fever notifications has been reported, it is unclear whether the reduction will be sustained, particularly as weekly rates of scarlet fever notification GP consultations remain above expected at this point of the season and are showing signs of fluctuation.

The recent declines in scarlet fever notification since week 49 may represent reduced levels of transmission. While these are often seen over the Christmas school break, this decline pre-dated the end of the school term. Public and healthcare professional alerts issued in week 48 (2 December 2022) may have succeeded in bringing people forward for clinical assessment and treatment, inducing the sharp increase in notifications in week 49 and reducing onward transmission. Ongoing monitoring will continue in the weeks following the start of the school term to assess the impact on transmission.

The rate of iGAS infection notifications across the season showed a similar pattern of elevation, with weekly incidence trending above what would be expected during the first part of the season, particularly during December.

While the rate of iGAS infection is elevated in all age groups, incidence in children aged under 10 years is particularly elevated compared to levels reported in the last peak season, and substantially higher than in the past 2 years. However, there continue to be indications of an increase of iGAS notifications in the older age groups in recent weeks; further epidemiological analysis will monitor this trend.

Investigations are underway following reports of an increase in lower respiratory tract GAS infections, particularly empyema, in children over the past few weeks (1). The current emm types have been circulating for many years. Whilst a new 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. The weekly incidence of iGAS in individuals over 75 years is higher than has been seen at this point in the season in pre-pandemic periods; the CFR in adults is slightly higher than for previous years at this point in the season, with emm1 dominant in this age group. Detailed genomic and biological investigations are underway 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 are likely to have resulted in increased levels of susceptibility to these infections in children, noting the very low levels during 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 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
• Weekly notifiable disease reports are published for a timelier update
• Group A strep – what you need to know (blog post)

Invasive disease isolates and also non-invasive isolates from suspected clusters or outbreaks should be submitted 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 31 January 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 31 January 2023.

The sharp increase in scarlet fever and other group A strep infections alongside increased awareness and vigilance amongst 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 to week 36 each year (mid-September to mid-September). The 2022 to 2023 season data within this report covers 12 September 2022 to 29 January 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 de-duplication has been implemented for this report, correcting an error which resulted in a small number of records being counted more than once in the mortality analyses in previous reports. The improved data cleaning process has been applied to current and previous seasons data presented in Table 3.

Population rates are calculated per 100,000 using the relevant year ONS mid-year population estimate. Rates have been updated to reflect the recent release of the 2021 mid-year population estimates.

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 a comparison point to the trends 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.

The support from colleagues within UKHSA, and the AMRHAI Reference Unit in particular, is valued in the preparation of the report.

Feedback and specific queries about this report are welcome via [email protected]