Polymerase chain reaction is superior to serology for the diagnosis of acute Mycoplasma pneumoniae infection and reveals a high rate of persistent infection.
BACKGROUND
Diagnosis of Mycoplasma pneumoniae (MP) infection is traditionally based on serology, which may require more than two weeks for diagnostic antibodies to develop. PCR-based methods offer earlier diagnosis. During a community outbreak of MP infection, we compared semi-nested and real-time PCR of oropharyngeal swabs with serology for diagnosis of MP infection at different time points after disease onset. PCR-positive individuals were followed longitudinally to assess the persistence of MP DNA in throat secretions. We also studied carriage of MP among household contacts and school children.


RESULTS
MP infection was diagnosed in 48 of 164 patients with respiratory tract infection. Forty-five (29%) had detectable MP DNA in oropharynx. A significant increase in MP IgG IgG titre or MP IgM antibodies was detected in 44/154 (27%) subjects. Two MP PCR-positive patients lacked antibody responses. Sera were missing from another two patients. The agreement between serology and PCR was good, kappa = 0.90. During the first three weeks after disease onset the performance of PCR was excellent and all patients but one were detected. In contrast, only 21% of the patients with confirmed MP infection were positive by serum 1 during the first symptomatic week (56% during the second and 100% during the third week). Only 1/237 (0.4%) school children was positive by PCR. This child had respiratory symptoms. Eighteen of 22 (75%) symptomatic household contacts were MP PCR positive. Persistence of MP DNA in the throat was common. Median time for carriage of MP DNA was 7 weeks after disease onset (range 2 days - 7 months). Adequate antibiotic treatment did not shorten the period of persistence. Bacterial load, measured by quantitative real-time PCR declined gradually, and all followed patients eventually became PCR-negative.


CONCLUSIONS
PCR is superior to serology for diagnosis of MP infection during the early phases of infection. Persistent, sometimes long-term, carriage of MP DNA in the throat is common following acute infection, and is not affected by antibiotic therapy. Asymptomatic carriage of MP even during an outbreak is uncommon.
Nilsson
Anna C
AC
Department of Clinical Sciences, Malmö, Infectious Disease Research Unit, Lund University, Malmö University Hospital, Sweden. Anna.c.nilsson@skane.se
Björkman
Per
P
Persson
Kenneth
K
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000907:Antibodies, Bacterial / Q000097:blood; D002648:Child; D002675:Child, Preschool; D004269:DNA, Bacterial / Q000235:genetics; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009177:Mycoplasma pneumoniae / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*; D009960:Oropharynx / Q000382:microbiology; D011019:Pneumonia, Mycoplasma / Q000175:diagnosis* / Q000453:epidemiology / Q000276:immunology / Q000382:microbiology; D016133:Polymerase Chain Reaction / Q000379:methods*; D012698:Serologic Tests / Q000379:methods*
D000907:Antibodies, Bacterial; D004269:DNA, Bacterial