Serodiagnosis of La Crosse virus infections in humans.

Serological diagnoses of human infections with California serogroup viruses are usually made by means of complement fixation or hemagglutination inhibition tests or both. An analysis of antibody titers in sera from 128 humans with California (La Crosse) virus infections indicated that exclusive use of the complement fixation tests would have detected only 50% of the actual seroconversions, whereas hemagglutination inhibition and neutralization tests alone would have been sufficient to make the diagnosis in 79.3% and 84.8% of the cases, respectively. These and other results presented demonstrate that the complement fixation test is not sufficiently useful as a primary tool for diagnosis of La Crosse virus infections. We suggest the use of the hemagglutination inhibition test for preliminary screening of sera from individuals with suspect infections caused by California serogroup viruses. The neutralization test should then be used or confirmation and subtype identification. If hemagglutination inhibition and neutralization titers are high and stable, the complement fixation test should then be used as a last, but specific, resort.