Antibody to the enterobacterial common antigen in normal human sera and in sera of acute pelvic inflammatory patients.

Antibody titres to Enterobacterial common antigen (ECA) were assayed in 482 serum specimens from healthy adults and in 40 serum specimens from patients with acute pelvic inflammatory disease by indirect haemagglutination. Normal levels of anti-ECA ranged from 1:4 to 1:256. The mean serum titre was 1:64. The titres were found to be maximal in subjects between ages 31 and 40. The serum titres of females were slightly higher than the titres of males. Significant increases in the titres of anti-ECA were found in 11 of the 17 anti-ECA positive patients who had no concomitant gonococcal infection. ECA antibodies in this study were mostly IgM. The IgG class of antibody was found in 1.1 percent.