Respiratory pathogens in children with and without respiratory symptoms

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Investigators from the Netherlands performed polymerase chain reaction (PCR) testing on respiratory samples taken every two weeks through a 6-month winter season from 18 children from infancy to 7 years of age. Study personnel contacted parents twice weekly to query about symptoms of respiratory tract illnesses. The PCR tests could detect 13 respiratory pathogens (11 viruses, Chlamydophila pneumoniae, and Mycoplasma pneumoniae).

A median of 9.5 symptomatic respiratory episodes occurred per subject over the 6-month study period. A pathogen was detected in 56% of symptomatic episodes (defined as onset of symptoms one week before or after sampling) and 40% of asymptomatic episodes. The youngest children had significantly fewer asymptomatic infections (9%) compared with the oldest children (36%) (P=0.03). Multiple pathogens were found in 17% of symptomatic episodes compared with 3% of asymptomatic episodes (P=0.02).

Despite some limitations of the study, including the small number of subjects and bi-weekly sampling performed by parents, the longitudinal design and robust detection of infectious agents contributes substantially to our knowledge of a non-bacterial “flora.” The ultimate balance of commensal versus pathogen and health versus symptomatology is undoubtedly tipped by host and environmental factors, as well as microbial factors.