Incidence of Subclinical Poliomyelitis in an Urban Area According to Age Groups

W ICKMAN recognized minor illnesses among the contacts of paralytic poliomyelitis cases.1 His postulation that these were mild forms of the disease, necessary to explain its epidemiologic behavior, was echoed in 1913 by Frost. Frost intimated that the paralytic case may perhaps be considered as a complication or accident in the course of poliomyelitis; that the disease occurs throughout the world in an endemic form, particularly in large cities; that the population of the cities becomes immunized by subclinical infection early in life, usually before 5 years of age (since older children and adults are less frequently attacked); that the disease has the seasonal distribution of enteric and insect-borne diseases, but that it is transmitted largely by person-to-person contact.2 Stocks estimated upward of 100 subclinical cases to each paralytic case in endemic areas.3 Evidence to support the above premises has gradually accumulated. Anderson and Frost reported that 1 of 5 normal adults and none of 3 normal children (ages 10, 11, and 16 years) had