Diagnosis by polymerase chain reaction of pneumonia caused by Legionella pneumophila in an immunocompetent child

A 10-year-old, previously healthy child with pneumonia caused by Legionella pneumophila diagnosed by polymerase chain reaction (PCR) of serum is presented. Diagnostic methods were PCR of serum using two different primer sets, and the detection of specific antibody in paired sera using an indirect immunofluorescence assay. Legionella DNA was amplified from serum obtained before and on day 6, but not after completion of a 14-day course of oral clarithromycin. The etiologic role of L. pneumophila was confirmed by seroconversion. The report illustrates that L. pneumophila PCR of serum may contribute to the identification of this microorganism as a cause of severe pneumonia in immunocompetent children.