Chapter 155: The Group A Streptococcus

INTRODUCTION

The group A Streptococcus (GAS), a β-hemolytic Streptococcus, presents significant clinical and public health challenges throughout the world. The magnitude of disease burden varies not only by geographic region and within countries, but also between distinct populations within regional or national borders. Currently, more than 600 million cases of GAS pharyngitis and 162 million cases of impetigo—a common presentation of GAS infection—are estimated to occur worldwide each year.^1,2 Although less common, invasive GAS infections, such as necrotizing fasciitis and streptococcal toxic shock syndrome (STSS), can result in death in 20–25% of cases.³ Nonsuppurative sequelae of GAS infection, such as acute rheumatic fever (ARF) and poststreptococcal glomerulonephritis (PSGN), are also major contributors to disease burden. A systematic review published in 2005 estimated that approximately 470,000 cases each of PSGN and ARF occur globally every year and between 15.6 and 19.6 million people were estimated to have rheumatic heart disease (RHD), a severe and chronic complication of ARF.¹ RHD is the leading cause of death from acquired heart disease among persons under 50 years of age, and from all cardiovascular disease among children in low income countries.^4–6 Because of the immense burden of disease, GAS continues to be an important target for prevention and public health control⁷.

Following a brief discussion of other groups of β-hemolytic streptococci, this chapter addresses the relevant basic biology, epidemiology, clinical manifestations, immune responses, treatment, and public health approaches to prevention and control of GAS infection in humans.

GROUPS OF B-HEMOLYTIC STREPTOCOCCI IN HUMANS AND ANIMALS

GAS is one of approximately 20 serogroups of β-hemolytic streptococci. Group classifications were developed by Rebecca Lancefield in the 1920s based on cell wall carbohydrate antigens.^8,9 The groups of public health importance are summarized in Table 155-1. Some species of streptococci express more than one group-specific antigen and are therefore included in more than one group category. For example, S. dysgalactiae subspecies equisimilis can express group A, C, G, and L antigens.¹⁰ While GAS colonizes or infects humans (although it has been reported to cause “big foot disease” in field voles and has very rarely been isolated from the throats of dogs^11,12), the other serogroups exhibit variable pathogenicity to humans and animals. Understanding the potential for zoonotic transmission of some β-hemolytic streptococcal serogroups is important for accurate diagnosis and appropriate clinical and public health management of streptococcal disease.