Sample collection.
Nasopharyngeal swabs were obtained annually from 40 randomly selected children in each village. Sampled children were independently selected year to year. At baseline, 12 months, and 24 months, 10 swabs per village were randomly selected for culture via broth dilution assay. At 36 months, approximately 15 swabs (mean, 14.6; range, 10 to 15) were randomly selected for culture.