Increased pharyngeal bacterial colonization during viral illness.

The oropharyngeal colonization by Staphylococcus aureus and Gram-negative bacilli (GNB) and its duration were studied in 89 house staff officers, with biweekly quantitative cultures for 11 months. Eighty-two episodes of upper respiratory tract infection were documented during the study period. The oropharyngeal colonization during illness-free periods ranged from 12% to 18% for GNB and from 5% to 14% for S aureus. During an episode of upper respiratory tract infection, the oropharyngeal colonization of GNB increased to 60%; S aureus colonization increased to 43%. The colonization with both GNB and S aureus was transient and lasted for approximately two weeks. The increased colonization by S aureus and GNB during a viral respiratory tract infection may be a factor contributing to the increased risk of pneumonia in patients with this condition.