LABORATORY EVALUATION OF A DOT-BLOT ENZYME-IMMUNOASSAY FOR SEROLOGIC CONFIRMATION OF ILLNESS DUE TO RICKETTSIA-CONORII

Of the 169 United States Army soldiers who deployed on a field trainin g exercise to a remote area of Botswana for two weeks in January 1992, more than 30% developed a febrile illness within five days of their r eturn. A diagnosis of South African tick typhus was suggested by soldi ers' exposure to ticks, as well as the presence of eschars and vesicle s at the site of tick bites, and tender regional lymphadenopathies. Th is high attack rate, experienced during such a short exposure period, emphasizes the hazard of illness due to Rickettsia conorii to persons visiting endemic areas. A rapid, diagnostic, semiquantitative enzyme i mmunoassay (DS) for detection of IgG and IgM antibodies to R. conorii was performed on 209 acute and convalescent sera from soldiers in the outbreak and on 75 control sera. For the acute sera from soldiers meet ing the probable case definition of having both regional lymphadenopat hy and tick bite eschar, as judged by an IgG indirect fluorescent anti body (LFA) test, the resulting sensitivity and specificity of the DS t est were 100% and 48%, respectively. In the analysis of the acute sera , the DS test identified as reactive more of the probable cases (62%) than either the IgG (16%) or IgM (55%) IFAs. This simple and rapid dia gnostic test could be useful in establishing a preliminary diagnosis o f R. conorii rickettsiosis in remote settings when immediate confirmat ion by IFA is impossible.