The effect of underreporting on the apparent incidence and epidemiology of XXXX .

@entity1 @entity99 @entity1956
To determine if passively reported cases of @entity99 are representative of the affected population, an active surveillance system was set up that identified all @entity1 in Pierce County, Washington, who had been diagnosed by a physician as having @entity99 in the period March 1 through August 31, 1984. In this county, this was part of an ongoing epidemiologic study of @entity99 that had previously included some stimulation of reporting. The active surveillance system covered all primary sources of medical care, including all private physicians who were most likely to see @entity1 with @entity99 . Secondary sources, those that did not provide direct medical care but might be aware of new cases, were also surveyed. The results of active surveillance showed that passive reporting was about 65% complete in Pierce County. No change occurred in the number of @entity99 cases reported, but @entity1956 cases increased by 50%, and non-A, @entity1956 cases increased by 138%. Most of the increase was a result of enhanced reporting from private physicians. The two risk groups most affected by underreporting were homosexual @entity1 with @entity1956 and blood transfusion recipients with non-A, @entity1956 . During active surveillance, the proportion of @entity1 with @entity1956 who reported homosexual activity was 52% compared with 20% from passive surveillance. Transfusion recipients represented 24% of the non-A, @entity1956 reported from active surveillance compared with 9% reported from passive surveillance. Although Pierce County may not be representative of all counties in the United States, @entity1 responsible for public health prevention programs should recognize that data acquired through passive surveillance may not accurately reflect the magnitude of the risk for specific populations or the amount of disease that can be prevented.
