Residual paralytic poliomyelitis in a tropical region of Brazil, 1969-1977: prevalence surveys in different age groups as indicators of changing incidence.

The magnitude of the problem of paralytic poliomyelitis in recent years in the tropical Federal District of Brazil was estimated in 1980 by determining the prevalence of residual paralytic poliomyelitis in 10,007 schoolchildren born in 1969-1970 and in 10,794 schoolchildren born in 1973-1974. About 98% of these children attended school in the Federal District. The rate of residual paralytic poliomyelitis of 5.4 per 1000 children born in 1969-1970 was 2.3 times higher than the rate of 2.3 per 1000 born in 1973-1974, which may be related to increasing vaccination of children under one year of age. Paralysis appeared before four years of age in 96.5% of these children. These prevalence rates indicate a minimal average annual incidence of acute persisting paralytic poliomyelitis of 187 cases per million total population during the period 1969-1973 and of 80 per million total population during the period 1973-1977 compared with an average annual incidence of 135 reported persisting and non-persisting paralytic cases per million total population in the United States in the prevaccine era and of four persisting cases per 100 million during 1973-1978.