1240 throat samples were processed during different seasons in 11 different communities of The Gambia (West Africa). The carriage rate for Haemophilus influenzae type b ranged from 0 to 33%, but often attained 10% or more, higher than that reported from other open communities. The duration of carriage was short (less than 3 mondis) and H. influenzae b was found in only 10% of the carriers isolated during the previous or the following survey. Children less than 5 years old carried H. influenzae b in their throat significantly more often than children older than 14 years (P<0·05). A high carriage rate did not correlate with the wet or dry season. The carriage rate of children in rural areas was similar to that of children in urban areas. Children in day-care centres or nurseries had a surprisingly low carriage rate (2%). The carriage rate of H. influenzae b was compared to the presence of H. influenzae subspecies in a random sample, which revealed that H. influenzae subspecies was found in 90% of the children under 5 years old. Encapsulated strains of H. influenzae were found in 25% of the same sample, two-thirds of which were not type b. All capsule types were represented. No meningitis cases occurred in the survey populations. We conclude that the prevalence of H. influenzae b in open Gambian communities is similar to that in closed communities elsewhere, but that the kinetics are different from those in closed communities, as persistance of infection in Gambian children is short-lived.

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