Performance of the OmcB Ct ELISA in selected populations. MIF CT-CP+: patients MIF C. trachomatis negative C. pneumoniae positive, HBD: healthy blood donors, MIF CT+CP-: patients MIF C. trachomatis positive C. pneumoniae negative, STI patients: patients referred to sexually transmitted infection clinics. *: Number of tested sera according to the population tested. Significant differences were found between the mean OD values of the OmcB Ct ELISA of children's sera as well as prostitutes' sera in comparison with those of the other populations tested (p < 0.01). No significant difference was found between the mean OD values of sera from patients MIF C. trachomatis positive, patients MIF C. pneumoniae positive, patients referred to STI clinics and from healthy blood donors.