Nancy A. Melville

June 27, 2012

June 27, 2012 (Thessaloniki, Greece) — As many as 20% of asymptomatic children carry the Mycoplasma pneumoniae, and the presence of the pathogen in the upper respiratory tract does not determine the etiology of a respiratory tract infection, according to research presented here at the European Society for Paediatric Infectious Diseases (ESPID) 30th Annual Meeting.

M pneumoniae is the culprit in up to 40% of community-acquired pneumonia cases; however, serology, the current gold standard for detecting infection, has its flaws, said coauthor Annemarie M. C. van Rossum, MD, from the Division of Pediatric Infectious Diseases and Immunology at Erasmus MC/Sophia Children's Hospital, Rotterdam, the Netherlands.

"The problem with serology is it is a retrospective diagnosis," said Dr. van Rossum. "Furthermore, the method is unreliable in young children, which is why we previously thought M pneumoniae was more prevalent in older children, and not so much [in children] under 5...[but] that is probably not true."

In an effort to take a closer look at the prevalence of M pneumoniae in children in the absence of respiratory tract infection, Dr. Van Rossum and colleagues evaluated 321 children admitted to the hospital with respiratory tract symptoms between July 2008 and September 2011 and compared them with 412 asymptomatic children who were admitted for other elective procedures.

Pharyngeal and nasopharyngeal samples and capillary blood samples were taken for detection of serum antibodies against M pneumoniae.

The samples also enabled the detection and quantification of genomic copies of M pneumoniae by real-time polymerase chain reaction (PCR), as well as the detection of other bacterial and viral respiratory pathogens.

The results showed M pneumoniae DNA to be present in 20.7% of the asymptomatic children and in 16.7% of children with a respiratory tract infection.

No significant differences in the distribution of genomic copy number or prevalence of anti–M pneumoniae serum-antibodies were seen between the 2 groups.

No differences in bacterial loads were seen between the children with infection and those without.

"We were curious about the levels of M pneumoniae in the healthy children, and while it was surprising to see 21% [prevalence], it confirmed our hypothesis," Dr. Van Rossum said.

"The rate is not statistically significant, but it is a reasonable amount for clinicians to have in the back of their minds in performing a PCR for M pneumoniae."

The patients in both groups were followed and sampled every month until they had 2 consecutive negative samples. Most of the patients in both groups were cleared of M pneumoniae.

"The results indicate that while M pneumoniae is highly prevalent in healthy children, longitudinal follow-up shows asymptomatic presence in the upper respiratory tract that typically clears in several weeks," Dr. Van Rossum said. "Caution should therefore be taken in the interpretation of diagnostic tests for M pneumoniae and [in] subsequent clinical management."

Dr. Van Rossum and colleagues are looking toward further investigation into the factors that determine progression from asymptomatic carriage of M pneumoniae to symptomatic infection.

"The aim of further studies is to generate diagnostic procedures that discriminate between carriage and symptomatic infection," she said.

The authors have disclosed no relevant financial relationships.

European Society for Paediatric Infectious Diseases (ESPID) 30th Annual Meeting. Presented May 11, 2012.

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