Asymptomatic carriage of M. pneumoniae common in children

The bacterium M. pneumoniae is carried at high rates in the upper respiratory tracts of healthy children and usual diagnostic tests cannot differentiate between such asymptomatic carriage and actual respiratory tract infection, according to a study by Dutch researchers published in this week's PLOS Medicine.

These findings are important as they suggest that clinicians may need to reconsider the clinical significance of a positive test result for the presence of this bacterium.

The researchers, led by Annemarie van Rossum from Erasmus MC–Sophia in Rotterdam, The Netherlands, reached these conclusions by comparing the upper respiratory tract swabs and blood culture results taken from 321 children (aged 3 months to 16 years) admitted to hospital with a respiratory tract infection with those from 405 healthy children undergoing an elective surgical procedure.

The authors found that the prevalence of M. pneumoniae (as measured using PCR tests) did not differ between the asymptomatic group and the symptomatic group, with a prevalence of 21.2% and 16.2% respectively. There was also no difference in prevalence when diagnosed using blood tests. In addition, a high rate of other bacteria and viruses was found in both asymptomatic and symptomatic children.

The authors also report a wide variation in asymptomatic carriage of M. pneumoniae ranging from 3% during the spring of 2009 to 58% during the summer of 2010. And in 21 children from the asymptomatic group who participated in a follow up study, 15 (71%) tested negative within one month and in the symptomatic group, 19 of 22 children (86%) tested negative after the first visit.

The authors say: "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 upper respiratory tract is common in asymptomatic children."

They continue: "The current diagnostic tests for M. pneumoniae are unable to differentiate between asymptomatic carriage and symptomatic infection."

The authors add: "Therefore, clinicians may need to readdress the clinical significance of a positive test result."