Invasive group A streptococcal (iGAS) infections have been reportable in BC since 1997.
Invasive group A streptococcal (iGAS) infections have been reportable in BC since 1997. Since that time, two periods of heightened activity have been observed: in 2008 when 259 confirmed cases were reported, and the period since late 2015. In 2016, 303 cases were reported (6.4 cases per 100 000 population); 209 cases have been reported from 1 January to 10 July 2017. The recent increase has been observed in all regions of the province but most notably in Vancouver Coastal Health, which reported 84 cases (12.5 cases per 100 000 population) in 2016 in the Vancouver Health Service Delivery Area. Cases occurred across the age span, with a mean age of 46 years, and the highest rates in the elderly. In 2016, 28% of iGAS cases were severe, defined as streptococcal toxic shock syndrome, necrotizing fasciitis, meningitis, pneumonia, or death. A similar proportion of cases were severe in the prior 9 years. The case fatality rate among 2016 cases was 7.9% with 24 deaths; one fatal case was in an adolescent and the others were over 40 years old.
Pediatric cases have been prominent in media coverage in 2017. There has been a slight increase in the proportion of cases under 15 years old: 11% compared to 8% in the 10 prior years. In 2017, two pediatric cases in children under 5 had fatal outcomes, whereas no deaths in children were reported in 2016. Also in 2017, an elementary school age child in the same classroom as an earlier invasive case experienced severe disease and survived with sequelae requiring rehabilitation. However, this disease is not common in children and secondary invasive cases are very rare. Instead, iGAS is most often associated with older age and underlying medical conditions including heart disease, diabetes, malignancy, alcoholism, and recent childbirth. Among 2016 cases, about 1 in 3 reported injection drug use. This risk group is recognized in the world literature as experiencing a higher rate of iGAS, most often associated with skin and wound infections.[2,3] Over 1 in 4 cases in 2016 reported being homeless/underhoused, another recognized risk factor. Varicella infection has been associated with a fiftyfold increase in iGAS but such cases have been reduced through routine childhood immunization.
Case confirmation is by isolation of Streptococcus pyogenes from a normally sterile site, typically blood, synovial fluid, or deep tissue taken at surgery for debridement in cases complicated by necrotizing fasciitis. iGAS isolates from normally sterile sites are typed at the National Microbiology Laboratory in Winnipeg using emm typing of the hypervariable region of the M protein gene. There are over 200 recognized strains. Emm 1 accounted for the highest proportion (17.4%) of cases in the 9 years prior to 2016, but was overtaken by emm 82 (20.2%) and 101 (16.8%) in 2016. While emm 1 was identified in half the 2016 cases in children under 15, among the cases reporting injection drug use or homelessness/underhousing, emm 82 and 101 were identified from 40.1% and 28.4% of cases with typing available, respectively.
While vaccines against iGAS are under development, at present the mainstay of reducing morbidity and mortality from this infection is recognition and treatment of pharyngeal and skin infections, and early recognition of invasive disease. Necrotizing fasciitis can be challenging to differentiate from cellulitis but severe pain and tenderness in excess of that expected with a superficial infection are the hallmark signs. Patients with streptococcal toxic shock syndrome typically present with fever and a widespread erythematous macular blanching sunburn rash, often with hypotension and with rapid progression requiring intensive care. Prompt administration of penicillin as the first-line antibiotic is recommended, although isoxazole penicillins (cloxacillin, dicloxacillin, flucloxacillin) are recommended when Staphylococcus aureus cannot be excluded. Clindamycin is an important adjunct for severe cases, with several biological mechanisms including direct effects on toxin production, as are surgical debridement of infected tissue and supportive care. Intravenous immunoglobulin and hyperbaric oxygen therapy have been used to improve outcomes in severe cases. Reporting of cases to public health will help to identify close contacts for antibiotic prophylaxis (recommended when the index case has severe disease); for associated infection control measures in specific settings such as day cares, nursing homes, and health care facilities; and recognition of clusters.
—Monika Naus, MD, MHSc, FRCPC, FACPM
—Samara David, MHSc
This article is the opinion of the BC Centre for Disease Control and has not been peer reviewed by the BCMJ Editorial Board.
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