From 1959 through 1962 all cases of hemorrhagic fever (HF) in Bolivia occurred in two rural areas about 70 miles apart, affecting mainly adult males. Although the town of San Joaquín (pop. 2500), Department of Beni, was spared, residents of nearby settlements and estancias were affected.
Then in late 1962 or early 1963 cases of HF began to occur frequently among San Joaquín residents who denied having been beyond the town limits during two or three weeks previous to illness. Since early 1963 we have attempted to determine the true frequency with which HF has occurred in San Joaquín and its surrounding area. Disease surveillance was limited to hospitalized cases in 1963, but was extended to non-hospitalized illness in 1964.
The complement fixation test (CFT) is the only serologic method so far adapted to routine epidemiologic use. To evaluate it as an epidemiologic tool, we tested 296 sera from 94 cases (who had previously shown a fourfold or greater rise in antibody titer by CFI') taken at intervals of up to 14 months after illness, using Machupo virus antigen.