Paired sera IgG test detects more Mycoplasma pneumonias infections than the single IgM test

Abstract

INTRODUCTION: M. pneumoniae is the causative agent of primary atypical pneumonia. Patients mount an IgM and IgG antibody response, which are useful diagnostic markers. The single serum test for IgM specific antibodies may be attractive for rapid laboratory diagnosis, due to delays or non-provision of the convalescent phase serum sample by patients. IgM antibodies are not always produced in adults upon reinfection. AIMS: To evaluate the diagnostic value of paired serum IgG testing compared to single serum IgM for diagnosis of M. pneumoniae infection. DESIGN, SETTING AND METHOD: A prospective clinical study was done involving 418 adult patients in Colombo North Teaching Hospital, Ragama and Chest Hospital, Welisara. {Pneumonia-97, acute bronchitis-183, pharyngitis-138). Control group-87 adults with no acute respiratory infections. M. pneumoniae specific IgG and IgM were tested in paired sera (taken 2-3 weeks apart) using an ELISA kit (IBL-Hamburg-Germany). RESULTS: Patients with >12 U/ml IgM response or IgG sero-conversion were considered positive for this infection. IgM response was detected in 27% (6/22) (4 - pneumonia, 2 - acute bronchitis) of the study population. IgG sero-conversion was detected in 64% (14/22) (9 - pneumonia, 10 - acute bronchitis, 2 - pharyngitis) and 9% (2/22) (2 -pneumonia) by both antibody types. In this study population, IgM specific antibodies were detected in 36% (8/22).There were no IgG responders in the control group but 2% (2/87) showed positive IgM response. CONCLUSION: Specific IgG testing with paired serum samples detect more cases of M. pneumoniae infection than the use of a single serum IgM test.