Human infection caused by Streptococcus suis serotype 2 in China: report of two cases and epidemic distribution based on sequence type

BACKGROUND: Streptococcus suis is a zoonotic pathogen that causes serious systemic infections in pigs and occupation-related infections in humans who contact with pigs or pork products. In China, it has caused two outbreaks of human infection and surveillance for S.suis has been ongoing since last time. CASE PRESENTATION: Two cases of meningitis and sepsis caused by S. suis were reported in this study. Both patients work in relation to the pork trade, a risk factor for S. suis infection. The outcome was favorable after a prolonged ceftriaxone therapy but one patient was left with mild hearing loss. Two isolates were identified as sequencing type (ST) 7, S. suis serotype 2 (SS2), which is one the most prevalent and cause two outbreaks in China. Whole-genome sequencing (WGS) revealed that a high degree identity was noted in the genome organizations and sequences between two sporadic ST7 SS2 isolates in this study and representative epidemic virulent isolates. Major differences among them are two sporadic ST7 SS2 isolates lacked a virulence factor called agglutinin receptor and an 89 K pathogenicity island (PAI), which plays important role in the pathogenesis of streptococcal toxic shock syndrome (STSS). A summary about STs of human infection with S. suis in China was completed. The result showed ST1 and ST7 were still the major STs and several novel STs were successfully discovered in different provinces. CONCLUSIONS: Our results enhanced the understanding of the ability to cause life-threatening infections in humans and the distribution and evolution of the S. suis in China.