Background: is a common cause of respiratory disease, but little is known about asymptomatic infection, duration of persistent respiratory tract infection and seasonal changes of prevalence in a normal large sample size pediatric population.
Methods: We studied the prevalence of infection in 1211 children of 3 age groups: 3- to 4-year-old kindergarten children ( = 184) and schoolchildren attending first and second ( = 353) or seventh and eighth grade classes ( = 674). Polymerase chain reaction and enzyme immunoassay detection (PCR-EIA) of throat swabs were used. Respiratory tract symptoms (cough, rhinitis, earache or sore throat) were recorded in 1028 schoolchildren. Follow-up examinations in PCR-positive patients were performed until negative.
Results: PCR was positive in 68 children (5.6%) without significant age and gender related differences in prevalence. Epidemics were confirmed with a prevalence up to 24% in a primary school in December and April. In schoolchildren, asymptomatic infection was a common feature, reaching 54% (32 of 59) of PCR-EIA positives. The rate of asymptomatic infection was 6% (32 of 531 schoolchildren without symptoms). Of the 32 asymptomatic PCR-EIA positives, 26 (81%) were children attending seventh and eighth grade classes. In 3 children PCR-EIA remained positive at 3 to 5 weeks and became negative during the next 7 to 9 weeks. One of 2 schoolchildren with persistent infection was asymptomatic.
Conclusions: We conclude that infection is common in the childhood population studied with seasonal variations in prevalence and epidemic-like occurrence. Asymptomatic infection occurs, especially in teenagers, but persistent infection is rare.