Q Fever Studies XV. Development and Persistence in Man of Complement-Fixing and Agglutinating Antibodies to Coxiella Burnetii

Discussion and Summary The time of appearance, increase in titer, and persistence of complement-fixing antibody against Coxiella burnetii was studied in 102 individuals. In addition, in 85 of the 102 patients, similar observations were made on the agglutinating antibody. Agglutinating antibody was detectable in the serum of 92% of the patients by the end of the second week, whereas complement-fixing antibody was detectable in only 65 per cent of the cases at this time. By the end of the third week, agglutinating and complement-fixing antibodies were detectable in the same proportion of patients, i.e., 95 and 97% respectively. At this time the median titers of both antibodies were in the range of 1:128–1:256. These findings suggest that the rickettsial agglutination test may have some advantages in the early diagnosis of Q fever. From the economic standpoint, however, the complement-fixation test is more readily adaptable to laboratory use. Also, it has been suggested in other rickettsial diseases that the complement-fixation test may be a better tool for epidemiologic surveys, since complement-fixing antibody has been observed to persist longer than the agglutinating antibody (16). From certain of the data presented here (charts E and F in Figure 3) concerning individual patients, it might also be inferred that in Q fever the complement-fixing antibody persists longer than the agglutinating antibody. However, if the patients are considered as a group (Figures 1 and 2) it would appear that the two antibodies in man are similar in their patterns of persistence; this would suggest that either the agglutination or complement-fixation test may be employed in serologic surveys. Parenthetically, it may be stated that in experimentally-inoculated large animals (sheep), the small amount of data available suggest, in general, that the agglutinating antibody appears early and tends to disappear within a few weeks (17); consequently, in surveys whose purpose is to detect remote as well as recent infections in livestock, it would appear that the complement-fixation test is the preferable method. The long persistence in man of both the agglutinating and the complement-fixing antibody emphatically underlines the need for caution in the interpretation of the results of serologic diagnostic tests performed on a single specimen of serum. The median titers of both antibodies in our series of patients remained at appreciably high levels for many months, so that a titer obtained on a single serum specimen cannot, in the absence of strong supporting epidemiologic and clinical evidence, be interpreted unequivocally as evidence of current infection with C. burnetii .