Use of antibiotics and risk factors for carriage of Streptococcus pneumoniae: a longitudinal household study in the United Kingdom.

This study aimed to identify risk factors and assess the impact of coincidental antibiotic therapy on carriage of Streptococcus pneumoniae. Index children from birth to 3 years and their households were recruited from primary health-care registers in four UK general practices. Nasopharyngeal swabs were taken monthly from study participants ten times between October 2001 and July 2002. Multilevel random-effect models were used to adjust for statistical dependence between repeated measurements and family clustering of carriage. Carriage results were available for 3753 swabs from 489 individuals in 121 families. Crude prevalence of carriage was 25%. On multivariable analysis, risk of carriage was reduced by antibiotic use the previous month [odds ratio (OR) 0.34, 95% confidence interval (CI) 0.22-0.52], but increased if a child attended day care for >20 h per week (OR 2.52, 95% CI 1.41-4.52). Taking antibiotics significantly reduces the risk of carriage the following month in a setting with a low prevalence of pneumococcal antimicrobial resistance.