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A prospective population-based field study on Haemophilus influenzae type b (Hib) meningitis was carried out in The Gambia, West Africa. The annual incidence was 60 cases/100,000 children less than 5 years old and 297 cases/100,000 less than 1 year. The peak incidence was in those 5 months old, and 45% of cases occurred in those less than 6 months. The case fatality rate was 37%. Because the outcome did not appear to be affected by the logistics of receiving care, and resistance to chloramphenicol and ampicillin is not yet a problem, prevention of Hib disease at an early age seems the best solution. There are several options for vaccine trials. On the basis of available data, at least one of these trials seems warranted before Hib vaccination can be introduced in developing countries. Extrapolation of successful results in industrialized countries to a population of different genetic origin and living under different conditions seems questionable.

One hundred two invasive and 64 noninvasive isolates of Haemophilus influenzae were collected in the course of a 2-year prospective field study on the epidemiology of H. influenzae meningitis in The Gambia. The isolates were serotyped, biotyped, and subtyped by outer membrane protein (OMP) profile analysis (OMP subtyping). H. influenzae meningitis was found to be caused by serotype b (95%). In invasive disease, serotype a, although present in the throat of healthy children, caused only occasionally (5.9%) disease. The distribution of biotypes of H. influenzae appeared to be very similar to that found outside The Gambia. A distinct pattern of OMP subtypes, different from other parts of the world, is prevalent in H. influenzae type b (Hib) in The Gambia. OMP subtypes 2, 4, 5, 8, and 9 were observed to be predominant. These subtypes, except subtype 2, have not been described. L subtypes (subtypes 2, 4, and 8) were associated with invasive disease, whereas non-L subtypes (subtypes 5 and 9) were found more often in healthy carriers (P less than 0.001). A significant difference in geographical distribution was found in subtypes of noninvasive Hib strains (P less than 0.05). We conclude that in The Gambia H. influenzae invasive disease is caused mainly by type b strains with a limited number of OMP subtypes, which are different from the subtypes found elsewhere in the world. These data are important for the surveillance of Hib disease in developing countries and are baseline data for a Hib polyribosyl-ribitolphosphate-conjugated vaccine trial in The Gambia. Alternative Hib OMP vaccines should include a set of representative OMPs.

Haemophilus influenzae meningitis was studied over a 2-year period in children less than 5 years of age in a population-based, prospective study in The Gambia, West Africa. A total of 77 cases were recorded. The incidence was 60 cases/100,000 children less than 5 years of age and 297 cases/100,000 children less than 1 year of age. The peak prevalence was at the age of 5 months; 83% of the children were less than 1 year old and 45% were less than 6 months old. Only 55% of cases recovered completely. The distance to the nearest hospital was an important predisposing factor for a fatal outcome. Two cases were secondary. Many patients were anemic and underweight. The observations show that H. influenzae meningitis in The Gambia has an incidence as high as that in the USA, but that it has 10-fold more devastating outcome. If the infection is to be prevented by vaccination in The Gambia, immunization will have to be given very early in life.

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 months) 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 less than 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 persistence of infection in Gambian children is short-lived.