[Saint Louis encephalomyelitis in Hermosillo, Sonora, Mexico. Its epidemiology].

In a warm desertic and irrigated region, with population 250 000 Northwest of Mexico, in Hermosillo, Sonora, along 8 weeks, 51 patients showed the following clinical data: fever, vomiting, neck rigidity, drowsiness and increase of cells and proteins in the CSF. In 12 patients good correlations were found between positive serologic results using SLE antigen by means of HI, CF and NT. Four paired sera showed fourfold increases in titers to SLE by means of HI or CF. With VEE antigen no such increases were found. The cases were scattered geographically, most of them occurred within an urban area, and affected people in 13 localities. The outbreak developed from August to September, 1974, the attack rate was 22/100 000, 69% of the patients being children under 15 years of age. The case fatality rate was 20%. A prosperous chicken industry existed in the region and epizootics were not reported in either domestic or wild animals at that time.