VALIDATION OF AN ENZYME-IMMUNOASSAY FOR SERODIAGNOSIS OF ACUTE Q-FEVER

An enzyme immunoassay was validated for the serodiagnosis of acute Q fever. Minimum positive tests were determined for both serial dilutions and a single dilution of patient sera. To establish the specificity of the test, 152 serum samples were tested from individuals with no evidence of past Coxiella burnetii infection. Diagnostic titers were set at greater than or equal to 128 for the IgM and IgG responses to phase I, at greater than or equal to 512 for the IgM response to phase II and at greater than or equal to 1,024 for the IgG response to phase II Coxiella burnetii These titers gave a false-positive rate of less than or equal to 1 %. Alternatively, testing a single dilution of sera (1:128) gave specificities ranging from 97.3 to 98.7 %. Tests with the greatest sensitivities, using serially diluted early convalescent-phase sera, were the IgM (84 %) and IgG (80 %) responses to phase II Coxiella burnetii. At a single serum dilution, 92 % of early convalescent sera had a positive IgG response to phase II Coxiella burnetii With a high specificity and good sensitivity, the EIA can be used to diagnose acute Q fever with a single convalescent serum specimen. The duration of a positive response was greater than five years.