Dynamics of pneumococcal carriage in adults: a new look at an old paradigm.

BACKGROUND Limited information is available on pneumococcal colonization among adults. We studied pneumococcal carriage dynamics in healthy adults using high-sensitivity approaches. METHODS Eighty-seven adults (25-50 years old), were followed for six months in Portugal. Nasopharyngeal, oropharyngeal and saliva samples were obtained monthly; pneumococcal carriers were also sampled weekly. Carriage was investigated by real-time PCR (targeting lytA and piaB) and culture. Positive samples were serotyped. RESULTS Approximately 20% of the adults were intermittent carriers; 10% were persistent carriers (>4 months). Pneumococcal acquisition and clearance rates were 16.5 (95% CI 11.2-24.2) and 95.9 (95% CI 62.3-145.0) cases/1000 persons-week, respectively. Living with children increased pneumococcal acquisition (HR:9.7, 95% CI 2.6-20.5; p<0.001). Median duration of carriage was seven weeks and did not depend on regular contact with children. CONCLUSIONS The pneumococcal carrier state in healthy adults is more dynamic than generally assumed: acquisition is frequent and duration of carriage is often long. This suggests that some adults may act as reservoirs of pneumococci and hence, depending on the social structure of a community, the magnitude of herd effects potentially attainable through children vaccination may vary. These findings are important when designing strategies to prevent pneumococcal disease in adults.