Epidemiological aspects of a poliomyelitis outbreak in Taiwan, 1982

Active surveillance was carried out to examine the epidemiological characteristics of an abrupt outbreak of poliomyelitis after a significant decline in incidence had resulted from a mass vaccination campaign. Through the intensive survey of private and public hospitals, a total of 1,058 paralytic cases were found with a sex ratio of 1.4. While the age-specific attack rate was highest for the age group of less than one year and decreased with increasing age, the age composition did show a greater proportion of higher age groups than in previous outbreaks. Among 901 cases with a known history of vaccination, about half had received no vaccination and only 9.7% had received three or more doses. The outbreak started on May 29th, peaked in late August and ended on November 1st. The epidemic spread from the north through the middle to the south of the island during this period. A simulated epidemic curve based on the Reed-Frost model fitted the observed one fairly well. Attack rates varied from county to county and were significantly associated with the community health status, vaccination coverage, and their interaction. Possible ways to prevent the epidemic are discussed.