Etiology and Epidemiology

The group A hemolytic streptococci are responsible for a range of afflictions other than scarlet fever, including erysipelas, rheumatic fever, and the sore throats known as tonsillitis in Great Britain and as pharyngitis in the United States. Scarlet fever is caused only by certain strains that produce (or release) a soluble toxin, whose absorption causes the rash characteristic of the disease. Different strains of streptococci produce different amounts of toxin. Epidemics thus vary greatly in severity, with mortality rates ranging from 0 to 30 percent. Transmission of the infection is by intimate contact, such as occurs in overcrowded homes and classrooms, and evidence of airborne or droplet nuclei infection is slight. In the past, scarlet fever occasionally occurred as a hospital infection, and the disease was also transmitted in contaminated milk.

Susceptibility to the skin rash differs according to the immune and hypersensitivity status of the individual. Those who have experienced scarlet fever once are unlikely to do so again, but remain vulnerable to streptococcal sore throats when exposed to infection with a new serologic type. Research on the susceptibility of different population groups, as defined by a positive skin test (Dick test), suggests that more than half of young infants are immune to the disease, but that by the age of 2 years, only some 20 percent remain so. Thereafter the proportion of im-munes rises steadily through childhood, reaching 77 percent at 10 to 15 years and 86 percent in adults.

The rare occurrence of second attacks of scarlet fever with rash is probably due to infection with a new antigenic erythrogenic toxin. The available evidence suggests that the geographic dominance of particular strains of scarlet fever streptococci is long-term, varying from country to country and from time to time. In Britain, during the years 1936 to 1956, type 4 streptococci were isolated more often from scarlet fever than from tonsillitis cases. In 1964-5, the commonest type associated with scarlet fever was type 4 in Britain, type 22 in East Germany, and type 1 in the former Soviet Union and Holland. With all types, the disease appears to follow a general pattern of alternate severity and mildness. At present, it is very common, though very mild, in both Europe and North America. Fatalities have ceased to occur, and the prevailing mildness of type means that cases tend to escape notification.

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