Abstract
Ranked among the top10 infectious causes of death worldwide, group A Streptococcus (GAS) causes small- and large-scale outbreaks, depending on the trigger as transmission of a GAS strain or expansion of predominant clones. In China, GAS infections other than scarlet fever are not notifiable. In Shanghai, an epidemiological investigation was initiated after two successive severe pneumonia cases with one death in a digital factory, from where outbreaks are less widely reported. The investigation was performed using emm typing, pulsed-field gel electrophoresis (PFGE) typing, superantigen profiling, and genome analysis. This enabled characterization of relatedness among the outbreak isolates and identification of the mobile genetic elements present. Among 57 patients with respiratory symptoms investigated in the factory, emm5 GAS strains were isolated from 8 patients. The eight GAS infection cases comprising one fatal severe pneumonia case, six influenza-like illness cases, and one pharyngitis case. Two risk factors were identified: adult with an age of 18–20 years and close contact with a GAS patient or carrier. GAS attack rate was 14.0% (8/57), and GAS carriage rate was probably around 2.7% (14/521) based on surveys in two nearby districts. All the 10 outbreak associated isolates were assigned to emm5 and sequence type ST-99 (emm5/ST-99), harbored superantigen genes speC, speG, and smeZ, and were assigned to two similar PFGE patterns (clones). Among the outbreak associated isolates, all carried ermA with resistance to erythromycin and inducible resistance to clindamycin, and eight (80%) carried a tetM gene with resistance to tetracycline. Among the 14 carriage isolates, 12 were emm12/ST-36, and 2 were emm1/ST-28, all with superantigen genes speC, speG, ssa, and smeZ. All the carriage isolates harbored ermB and tetM with resistance to erythromycin, clindamycin, and tetracycline. Genome analysis showed the two outbreak clones were closely related and possessed new prophages carrying virulence gene sdc and antibiotic resistance genes of ermA and tetM, which were not found in the emm5 reference strain Manfredo. This is the first report of a GAS outbreak in this type of workplace. The outbreak was caused by two closely related emm5 clones that differed from the predominant emm types circulating in China.
Highlights
Streptococcus pyogenes, one of the top10 infectious causes of death worldwide (Excler and Kim, 2016), is known as group A Streptococcus (GAS)
Two severe cases aged 18–20 years were transferred to a grade three hospital and one of them was dead on October 9
Sputum, and throat swab were collected from patients with respiratory symptoms in the factory on October 9, October 11 (n = 31), and October 14 (n = 20)
Summary
Streptococcus pyogenes, one of the top infectious causes of death worldwide (Excler and Kim, 2016), is known as group A Streptococcus (GAS). The only notifiable disease among all the GAS infections in China (Yang et al, 2013b), has been epidemic in Hong Kong and mainland China since 2011, with an incidence of 21.7– 31.4/100,000 population (Lau et al, 2012; Yang et al, 2013b) This large outbreak is caused mainly by emm GAS, and typically infects children attending kindergarten and school (97%) (Chen et al, 2012). Variants of ICE-emm and HKU.vir were found to be transferred horizontally between emm and emm strains This conferred enhanced virulence and multidrug resistance in emm strains and elevated their proportion in scarlet fever isolates (Ben Zakour et al, 2015). It was considered appropriate to analyze whether the outbreak strains carry MGEs associated with toxin production and antimicrobial resistance
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