Background: Mycoplasma pneumoniae is thought to be a common cause of respiratory tract infections (RTIs) in children. The diagnosis of M. pneumoniae RTIs currently relies on serological methods and/or the detection of bacterial DNA in the upper respiratory tract (URT). It is conceivable, however, that these diagnostic methods also yield positive results if M. pneumoniae is carried asymptomatically in the URT. Positive results from these tests may therefore not always be indicative of a symptomatic infection. The existence of asymptomatic carriage of M. pneumoniae has not been established. We hypothesized that asymptomatic carriage in children exists and investigated whether colonization and symptomatic infection could be differentiated by current diagnostic methods.
Methods and findings: This study was conducted at the Erasmus MC-Sophia Children's Hospital and the after-hours General Practitioners Cooperative in Rotterdam, The Netherlands. Asymptomatic children (n = 405) and children with RTI symptoms (n = 321) aged 3 mo to 16 y were enrolled in a cross-sectional study from July 1, 2008, to November 30, 2011. Clinical data, pharyngeal and nasopharyngeal specimens, and serum samples were collected. The primary objective was to differentiate between colonization and symptomatic infection with M. pneumoniae by current diagnostic methods, especially real-time PCR. M. pneumoniae DNA was detected in 21.2% (95% CI 17.2%-25.2%) of the asymptomatic children and in 16.2% (95% CI 12.2%-20.2%) of the symptomatic children (p = 0.11). Neither serology nor quantitative PCR nor culture differentiated asymptomatic carriage from infection. A total of 202 children were tested for the presence of other bacterial and viral pathogens. Two or more pathogens were found in 56% (63/112) of the asymptomatic children and in 55.5% (50/90) of the symptomatic children. Finally, longitudinal sampling showed persistence of M. pneumoniae in the URT for up to 4 mo. Fifteen of the 21 asymptomatic children with M. pneumoniae and 19 of the 22 symptomatic children with M. pneumoniae in this longitudinal follow-up tested negative after 1 mo.
Conclusions: Although our study has limitations, such as a single study site and limited sample size, our data indicate that the presence of M. pneumoniae in the URT is common in asymptomatic children. The current diagnostic tests for M. pneumoniae are unable to differentiate between asymptomatic carriage and symptomatic infection.