The Prevalence of Potential Pathogenic Bacteria in Nasopharyngeal Samples from Healthy Children and Adults

Objective: To elucidate the prevalence of potential pathogenic bacteria in nasopharyngeal samples from healthy individuals, and the influence on the carrier rate of age, season of the year, and type of child day care.

Design: Nasopharyngeal swab samples obtained in routine medical care from individuals with no sign of infection were studied in 159 pre-school children aged below 7 years, 198 schoolchildren aged 7-15 years, and 261 adults (.16 years).

Results: The prevalence of pathogenic bacteria in healthy individuals decreased with age. The overall isolation frequencies for pre-schoolchildren, schoolchildren, and adults, respectively, were: Moraxella catarrhalis (27%, 4% and 2%); Streptococcus pneumoniae (19%, 6% and 0.8%); Haemophilus influenzae (13%, 6% and 3%). The prevalence of S. pneumoniae in children 7-15 years was higher during the summer than in the winter. We could not confirm any variation in the carrier rate due to the type of child day care.

Conclusion: Potentially pathogenic bacteria are often present in nasopharyngeal samples taken from healthy pre-school children, but rarely from people > or = 16 years of age. This means that the use of nasopharyngeal samples to discriminate between bacterial and viral respiratory tract infection needs to be evaluated further in patients < 16 years. The importance of the seasonal variation in the prevalence of potential pathogenic bacteria in the nasopharynx needs further study.