Invasive Group A Streptococcal Disease. National Epidemiology and Genetic Analysis

Abstract

Infections with group A streptococci (GAS), or S. pyogenes, range from mild and superficial to very severe and lethal invasive disease. In severe invasive GAS infections, hypotension and multiorgan failure may develop rapidly resulting in the development of toxic shock-like syndrome (TSS). In the northern part of the world's Western Hemisphere, a high endemic level of GAS infection in the 19th century was followed by a spontaneous decline. Nonetheless, a resurgence of fulminant invasive GAS infections was noted in the late-1980s. Because of the unexpected resurgence of this dramatic bacterial disease, a prospective population-based national surveillance program on invasive GAS disease was initiated in The Netherlands in1992. The aim of this thesis was to gain understanding in the epidemiology of invasive GAS infections in the Netherlands and to investigate the relationship between the genetic composition of the bacterium and its clinical and epidemiological manifestations. From 1992 through 1996, a total of 880 patients with invasive streptococcal disease were clinically evaluated. Based on antigenic differences in their M-protein, GAS can be further subdivided. Predominant M-types were M1 (21%), M3 (11%), M6 (5%), M12 (5%), and M28 (8%). The case-fatality rate was 18% overall, but it reached 59% among cases of TSS. Older age, necrotizing fasciitis, sepsis without focus, pneumonia, infection with type M1 or M3 strains, and underlying cardiopulmonary disease were associated with fatality. For long term GAS disease surveillance, invasive isolates were obtained from 1504 patients from May 1994 until December 2003. There was a clear seasonal pattern in invasive streptococcal infections, with an estimated annual incidence that peaked in 1996 (4.0 cases / 100 000 individuals / year) and was at its lowest in 1999 (2.0 cases / 100 000 individuals / year). Since GAS virulence appears to be determined by a complex interplay between multiple virulence factors rather than a limited number of genes only, we constructed a mixed-genome microarray. Microarray analysis revealed that inter M-type differences clearly outweighed intra M-type differences on a whole genomic level. Genetic variation between and within M-types was largely attributable to phages or phage-like elements. Using the mixed-genome microarray technique we could identify biomarkers that were uniquely present among M1 and M3 strains. Further research is required to establish whether these biomarkers contribute to specific M1 and M3 characteristics, such as their TSS inducing potential and association with necrotizing fasciitis. We hypothesized that acquisition of novel genetic elements could have created unusually successful clones the, thus explaining the increase in frequency and severity of invasive GAS infections in the late1980s. Mixed-genome DNA-DNA microarray analysis showed that contemporary M1 and M28 strains in The Netherlands have evolved from ancestral strains through a series of transduction events: the core genome of all strains was identical and variation in prophage content accounted for the differences in genome composition over time. Acquisition of phage-encoded virulence factors is likely to have contributed to an overall increase in GAS virulence over time.