Abstract
Invasive group A streptococcal infection has a 15% case fatality rate and a risk of secondary transmission. This retrospective study used two national data sources from England; enhanced surveillance (2009) and a case management system (2011–2013) to identify clusters of severe group A streptococcal disease. Twenty-four household pairs were identified. The median onset interval between cases was 2 days (range 0–28) with simultaneous onset in eight pairs. The attack rate during the 30 days after first exposure to a primary case was 4,520 per 100,000 person-years at risk (95% confidence interval (CI): 2,900–6,730) a 1,940 (95% CI: 1,240–2,880) fold elevation over the background incidence. The theoretical number needed to treat to prevent one secondary case using antibiotic prophylaxis was 271 overall (95% CI: 194–454), 50 for mother-neonate pairs (95% CI: 27–393) and 82 for couples aged 75 years and over (95% CI: 46–417). While a dramatically increased risk of infection was noted in all household contacts, increased risk was greatest for mother-neonate pairs and couples aged 75 and over, suggesting targeted prophylaxis could be considered. Offering prophylaxis is challenging due to the short time interval between cases emphasising the importance of immediate notification and assessment of contacts.
Highlights
Group A Streptococcus (GAS) causes a range of illnesses, from the relatively mild pharyngitis to severe, life-threatening disease [1]
Data from 2010 were excluded as the HPZone system was implemented that year and it was not possible to confirm that all data were captured and Invasive GAS (iGAS) infection became a notifiable disease in England from 2010 [13], data were likely to be incomplete
In 2009, an additional 15 case records reported a link to another GAS case
Summary
Group A Streptococcus (GAS) causes a range of illnesses, from the relatively mild pharyngitis to severe, life-threatening disease [1]. Invasive GAS (iGAS) infection has a case fatality rate exceeding 15% [2] rising to 25% in resource-limited countries [1]. Kingdom (UK), iGAS has an estimated incidence rate of 3.33 per 100,000 population per year [3]. Other contacts are systematically followed up to inform them of their increased risk and advised to seek medical care if they have symptoms of GAS infection or develop them within 30 days from exposure [7,8]. The Public Health Agency of Canada recommends selective prophylaxis for household contacts when a case is fatal or presents with severe symptoms including streptococcal toxic shock syndrome, soft-tissue necrosis, meningitis or pneumonia [11]. A We estimated the background incidence using the proportion of cases that were residents in the community and acquired iGAS in the community which was. The estimated proportion excluded care home residents and hospital acquired cases. b Calculated using ONS maternity data, this represents the estimated risk for the mother and neonate during the month after birth. c Background incidence for all 75 year-olds and over
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