Characteristics of group A Streptococcus strains circulating during scarlet fever epidemic, Beijing, China, 2011.

Streptococcus pyogenes, also known as group A Streptococcus (GAS), is a common human pathogen that can induce a wide spectrum of diseases, ranging from noninvasive diseases, such as pharyngitis, scarlet fever, and impetigo, to invasive diseases, such as erysipelas, cellulitis, pneumonia, bacteremia, necrotizing fasciitis, and toxic shock syndrome. Moreover, GAS can cause rheumatic fever and acute poststreptococcal glomerulonephritis (1,2). In the late1980s, a change in the epidemiology of invasive GAS diseases and the emergence of streptococcal toxic shock syndrome were documented (3,4), and the current number of invasive GAS disease cases worldwide is high (2). Many virulence factors contribute to the pathogenesis of GAS diseases (1,5). However, the matrix (M) protein, encoded by the emm gene, has the most critical role, mainly by antiphagocytic mechanisms (6,7), and the amino-terminal region of M protein is the most promising target for designing a vaccine (8,9). emm gene sequencing is a standard method for typing the M protein (10), but the distribution of emm types varies greatly by geographic location, time, and collection site of clinical specimens (9,11–14). Streptococcal pyrogenic exotoxins also play a major role in the pathogenesis of GAS infections by acting as superantigens. When these exotoxins cross-link major histocompatibility complex class II molecules and T cell receptors, they trigger intense activation of a subset of T cells within a specific β-chain variable region. This process induces a tremendous release of a series of cytokines and may lead to cell, tissue, and organ damage (15,16). Several antimicrobial drugs effectively treat GAS infections (1). In recent years, however, considerable attention has been given worldwide to the issue of antimicrobial drug–resistant GAS. Macrolide-resistant GAS strains have been isolated from various regions of the world (17–19). Macrolides are used as an alternative treatment for GAS in patients allergic to penicillin, and clindamycin, in combination with β-lactam antimicrobial drugs, is a recommended treatment for invasive GAS disease (20). Thus, it is critical that surveillance for macrolide- and clindamycin-resistant GAS be continued. In China, scarlet fever is the only GAS disease reported by the National Notifiable Infectious Disease Surveillance System (NNIDSS) (21). According to NNIDSS, the incidence of scarlet fever in Beijing, China, before 2011 had persistently remained within normal threshold limits. However, in late spring 2011, an epidemic of scarlet fever occurred in Beijing and many other regions of China. In response to the epidemic, enhanced surveillance for GAS diseases was conducted in Beijing during May–July 2011 to determine characteristics of the circulating GAS strains.