Severe streptococcal infections in historical perspective.

The recent unexplained increase in severe streptococcal diseases in the United States and Great Britain is compared to the 1825-1885 pandemic of fatal scarlet fever. Although scarlet fever may not be representative of all severe streptococcal disease, it was the only one reliably identified in the 19th century. The epidemiology of scarlet fever during the 19th century pandemic suggests the following features of the disease; cocirculation of both virulent and less-virulent streptococcal strains eliciting cross-immunity; circulation of hyperendemic prevalent strains in urban centers of developed nations, with periodic spillovers to rural areas and developing nations; and protection of infants from infection (but not from fatal disease once infection occurred) by the transfer of maternal antibodies via the placenta, breast milk, or both. The 19th century data suggest that efforts to prevent severe streptococcal diseases should begin with better characterization of the epidemiology of streptococcal disease, a task entailing identification of streptococcal virulence factors and measurement of their distribution among isolates from individuals with streptococcal diseases and in open populations.