Abstract 1034 Poster Session IV, Tuesday, 5/4 (poster 119)

Sera from 54 cases and 55 controls were studied quantitatively for IgA and IgG antibodies to B. pertussis antigens PT, FHA, and PRN by ELISA; for B. pertussis agglutinogens by agglutination; for C. pneumoniae IgM and IgG by IFA and for M. pneumoniae IgM by qualitative ELISA and for M. pneumoniae IgG by quantitative ELISA. The distribution of IgA and IgG PT and PRN antibodies and agglutinin titers (Aggs) were similar in cases and controls whereas the FHA, IgA and IgG median values were significantly higher in the cases than in the controls and 35% of the IgG values in the cases were above the 95th percentile of the controls (p=0.0001). C. pneumoniae IgG titers ≥512 occured in 33% of cases and in only 16% of controls (p=0.04) and M. pneumoniae IgM antibody occured in 61% of cases and in only 31% of controls (p=0.002). In contrast, median IgG M. pneumoniae values were significantly higher in the controls (p=0.001). More cases than controls had both M. pneumoniae IgM and high FHA (24% vs 2%; p=0.0005); M. pneumoniae IgM and C. pneumoniae IgG titers ≥512 (24% vs 7%; p=0.016); C. pneumoniae IgG titers ≥512 and high FHA (13% vs 0%; p=0.006); and M. pneumoniae IgM, C. pneumoniae IgG titers ≥ 512 and high FHA (11% vs 0%, p=0.01). These data suggest that both M. pneumoniae and C. pneumoniae contributed to illness in the cases. The finding of an increased prevalence of M. pneumoniae IgM antibody in the cases but higher quantitative IgG titers in the controls is unexpected and unexplained. The elevated FHA values without elevated PT, PRN, or Aggs is not consistent with B. pertussis illness. The high FHA values suggest the possibility of B. parapertussis or B. bronchosepticum infections but infection with these 2 agents would also likely cause a raise in PRN values. Therefore it seems likely that the high FHA values reflect cross reacting antibodies to an unidentified cough causing agent or agents and/or to M. pneumoniae or C. pneumoniae or both. Our data suggest that antibody to FHA without antibody to other B. pertussis antigens may be unreliable for the serologic diagnosis of B. pertussis infections.