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Volume 8 No 11; 21 March 2014

Group A streptococcal infections: update on seasonal activity, 2013/14

National surveillance data for group A (Streptococcus pyogenes; GAS) streptococcal infections continue to show increases in incidence above the seasonally expected levels for England. Further to the previous report of 4 March 2014 [1], scarlet fever notifications have escalated across the country. Routine laboratory reports and isolate referrals are showing early signs of a possible elevation of invasive group A streptococcal (iGAS) disease incidence.

Scarlet fever

Routine monitoring of surveillance data identified widespread increases in scarlet fever notifications in February 2014 compared to recent years (figure 1). These increases continued into March, with weeks 10 and 11 of 2014 being particularly high, where numbers of notifications surpassing levels seen in the last peak year (2008/09). A total of 3548 notifications of scarlet fever have been made so far this season in England (weeks 37 2013 to 11 2014) compared to an average of 1420 (range: 807 to 2622) for this same period in the previous 10 years. The last season to have this level of scarlet fever activity was 1989/1990 where 4042 notifications were received by week 11. The age distribution of cases notified so far for this season remains similar to previous years, with 87% being children under 10y (median 4y).

Figure 1. Weekly scarlet fever notifications in England, 2008/09 onwards



The increase in scarlet fever has been seen across different areas in England with the highest rate of notifications per 100,000 population being in Cheshire and Merseyside (13.0), East Midlands (11.9), Avon Gloucestershire and Wiltshire (10.6), Thames Valley (9.5) and North East (9.7) (figure 2). Four PHE Centre areas are reporting an incidence of scarlet fever similar to last year, North East, Yorkshire & Humber (6.4), Wessex (5.3) and Greater Manchester (8.1) although their rates were relatively high last year (9.5, 6.8, 5.7 and 8.5 in 2013 respectively).

Figure 2. Rate per 100,000 population scarlet fever notifications in England by Public Health England Centre, week 37, 2013, to week 11, 2014

A total of 680 iGAS isolates, defined as isolation of GAS from a normally sterile site, were referred to the Respiratory and Vaccine Preventable Bacteria Reference Unit at Colindale PHE from laboratories in England, Wales and Northern Ireland for specimens taken this season (week 37 2013 to 11 2014), a slight increase on the average (621 reports) but within the range (509-755 reports) for the same period in the previous five years (figure 3).

Three English regions have referred slightly higher than average (2009 to 2013) iGAS isolates for January and February 2014 (combined), East Midlands (25 isolates), London (39 isolates) and the North West (44 isolates). All other regions in England are referring lower numbers of isolates than normal for this time of year.

Antimicrobial susceptibility results from routine iGAS laboratory reports for the season so far indicate erythromycin non-susceptibility is at 6%, which is within the usual range. The susceptibility testing of iGAS isolates against other key antimicrobials (tetracycline (11%), clindamycin (2%) and penicillin (0%)) indicate no changes in resistance. There have been no reports of penicillin resistance in iGAS isolates in England to date.

Figure 3. Weekly count of sterile site GAS isolates referred to the national reference laboratory, England, 2008/09 onwards

Characterisation of iGAS isolates referred to the Respiratory and Vaccine Preventable Bacteria Reference Unit from laboratories in England is identifying a slight shift in the emm/M-type distribution, with an increase in emm 3 in February, with 23% of referrals being emm 3 (compared with 16% in January). Given the increased severity of disease associated with emm 3 strains, this warrants increased monitoring.

Analysis of scarlet fever notifications over the last century suggest cyclical patterns of incidence, with resurgences occurring on average every four years [2]. The last peak year for scarlet fever was 2008/09, with superficial manifestations of GAS infection tending to mirror those of invasive disease [3]. Whilst the enhanced media coverage and public health alerts may have increased case ascertainment, the escalation prior to this suggests a genuine increase in disease incidence. The reasons behind this increase are unclear but may be attributable to a natural cycle in disease incidence. The potential for changes in virulence of circulating strains or increased incidence in particular risk groups remain possible and as such continued vigilance remains essential.

Clinicians, microbiologists and HPTs should continue to be mindful of potential increases in invasive disease and maintain a high index of suspicion in relevant patients as early recognition and prompt initiation of specific and supportive therapy for patients with iGAS infection can be life-saving. Invasive disease isolates and those from suspected clusters or outbreaks should be submitted to the Respiratory and Vaccine Preventable Bacteria Reference Unit at Public Health England, 61 Colindale Avenue, London NW9 5HT.

Guidelines on infection control in schools and other childcare settings, including recommended exclusion periods for scarlet fever, can be found on the following on: http://www.hpa.org.uk/Topics/InfectiousDiseases/InfectionsAZ/SchoolsGuidanceOnInfectionControl/

FAQs on scarlet fever can be found on: http://www.hpa.org.uk/Topics/InfectiousDiseases/InfectionsAZ/ScarletFever/

Guidelines for the management of close community contacts of invasive GAS cases [4] and the prevention and control of GAS transmission in acute healthcare and maternity settings [5] are also available on the web: http://www.hpa.org.uk/Topics/InfectiousDiseases/InfectionsAZ/StreptococcalInfections/Guidelines.

References

1. Public Health England. Group A streptococcal infections: seasonal activity, 2013/14. Health Protection Report 2014; 8(9): Infection (News) Report. Available from: http://www.hpa.org.uk/hpr/archives/2014/hpr0914_AA_GASnws.pdf.

2. Lamagni T, Dennis J, George R, Efstratiou A. Analysis of epidemiological patterns during a century of scarlet fever. European Scientific Conference on Applied Infectious Disease Epidemiology; 18 November 2008; Berlin, Germany; 2008.

3. Dennis JN, Lamagni TL, Smith GE, Elliot AJ, Loveridge P, George RC et al (2008). Use of primary care syndromic data to forecast rises in invasive group A streptococcal disease. Health Protection Conference, 15 September 2008; Warwick.

4. Health Protection Agency Group A Streptococcus Working Group. Interim UK guidelines for management of close community contacts of invasive group A streptococcal disease. Commun Dis Public Health 2004; 7(4): 354-361.

5. Steer JA, Lamagni TL, Healy B, Morgan M, Dryden M, Rao B et al. Guidelines for prevention and control of group A streptococcal infection in acute healthcare and maternity settings in the UK. J Infect 2012 Jan; 64(1):1-18.