Clinical and microbiologic characteristics of invasive Streptococcus pyogenes infections in north and south India

The lack of epidemiologic data on invasive Streptococcus pyogenes infections in many developing countries is concerning, as S. pyogenes infections are commonly endemic in these areas. Here we present the results of the first prospective surveillance study of invasive Streptococcus pyogenes infections in India. Fifty-four patients with invasive S. pyogenes infections were prospectively enrolled at two study sites, one in the north and one in the south of India. Sterile-site isolates were collected, and clinical information was documented using a standardized questionnaire. Available acute-phase sera were tested for their ability to inhibit superantigens produced by the patient's own isolate using a cell-based neutralizing assay. The most common clinical presentations were bacteremia without focus (30%), pneumonia (28%), and cellulitis (17%). Only two cases of streptococcal toxic shock syndrome and no cases of necrotizing fasciitis were identified. Characterization of the isolates revealed great heterogeneity, with 32 different emm subtypes and 29 different superantigen gene profiles being represented among the 49 sterile-site isolates. Analyses of acute-phase sera showed that only 20% of the cases in the north cohort had superantigen-neutralizing activity in their sera, whereas 50% of the cases from the south site had neutralizing activity. The results demonstrate that there are important differences in both clinical presentation and strain characteristics between invasive S. pyogenes infections in India and invasive S. pyogenes infections in Western countries. The findings underscore the importance of epidemiologic studies on streptococcal infections in India and have direct implications for current vaccine developments.