Increased prevalence of group A streptococcus isolates in streptococcal toxic shock syndrome cases in Japan from 2010 to 2012

Abstract

Streptococcal toxic shock syndrome (STSS) is a severe invasive infection characterized by the sudden onset of shock, multi-organ failure, and high mortality. In Japan, appropriate notification measures based on the Infectious Disease Control law are mandatory for cases of STSS caused by β-haemolytic streptococcus. STSS is mainly caused by group A streptococcus (GAS). Although an average of 60-70 cases of GAS-induced STSS are reported annually, 143 cases were recorded in 2011. To determine the reason behind this marked increase, we characterized the emm genotype of 249 GAS isolates from STSS patients in Japan from 2010 to 2012 and performed antimicrobial susceptibility testing. The predominant genotype was found to be emm1, followed by emm89, emm12, emm28, emm3, and emm90. These six genotypes constituted more than 90% of the STSS isolates. The number of emm1, emm89, emm12, and emm28 isolates increased concomitantly with the increase in the total number of STSS cases. In particular, the number of mefA-positive emm1 isolates has escalated since 2011. Thus, the increase in the incidence of STSS can be attributed to an increase in the number of cases associated with specific genotypes.

Keywords: streptococcal toxic shock syndrome.

Fig. 1.

The number of emm genotypes of strains isolated from patients of streptococcal toxic shock syndrome (STSS) in 2010, 2011, and 2012. Values in parentheses indicate the number of isolates collected annually. The line graph indicates the rate of incidence of group A streptococcus (GAS)-induced STSS per 100 000 individuals in each year (2010, 0·066; 2011, 0·113; 2012, 0·121). The number of GAS-induced STSS cases reported in each year is also recorded: 2010, n = 86; 2011, n = 143; 2012, n = 154.

Fig. 2.

Mortality rates (in %) according to the different emm types. Values in parentheses indicate the number of isolates that outcome has become clear for in each emm genotype. Y-axis indicates the mortality rate in each emm genotype.

Fig. 3.

Sequence comparison of the sic alleles from streptococcal toxic shock syndrome isolates (n = 131) collected in Japan. The sic gene was utilized to create a phylogenetic tree. The numbers in parentheses indicate the number of isolates in each sic genotype.