In order to explain a threefold increase in the incidence of meningococcal disease in the Netherlands during the 1980s, we serotyped and subtyped Neisseria meningitidis isolates recovered between 1958 and 1990 from > 3,000 patients with systemic disease. No single strain could be held responsible for the increase. Apart from the newly introduced strain B:4:P1.4, which became the most prevalent phenotype in 1990 (21% of all isolates), the majority of the cases in 1990 were caused by many different strains that were already present in the Netherlands before 1980. For the period 1980-1990, a shift in the age distribution of patients with meningococcal disease from younger to older age categories was found, particularly with regard to cases due to meningococci of serogroup B; this shift is explained by the changing distribution of serotypes and subtypes within serogroup B. A polyvalent group B, class 1 outer-membrane-protein vaccine of a stable composition could theoretically have prevented approximately 80% of all group B meningococcal infections in the Netherlands during the past 30 years.

Several properties of Haemophilus influenzae outer membrane proteins were analyzed to define related proteins in various isolates. H. influenzae type b 760705 had six major outer membrane proteins with the following characteristics. Protein a (Mr, 47,000) demonstrated heat modifiability in sodium dodecyl sulfate; its apparent molecular weight was 34,000 at temperatures below 60°C. This protein was extracted from cell envelopes by using Triton X-100-10 mM MgCl2; in cell envelope preparations, the protein was degraded by trypsin. Proteins b (Mr, 41,000) and c (Mr, 40,000) were insensitive to trypsin degradation, were not heat modifiable in sodium dodecyl sulfate, and were peptidoglycan associated in 0.5% Triton X-100-0.2% sodium dodecyl sulfate. The amount of protein b was reduced in ultrasonically obtained cell envelopes. Protein d (Mr, 37,000) was heat modifiable in sodium dodecyl sulfate with an Mr of 28,000 at temperatures below 100°C and was degraded by trypsin, leaving a membrane-bound fragment of Mr, 27,000. Both the intact and degraded proteins were immunologically crossreactive with the heat-modifiable OmpA protein of Escherichia coli K-12. Protein d was absent in LiCl-EDTA extracts of cells. Protein e (Mr, 30,000), invariably present in all H. influenzae strains tested, was insensitive to trypsin and absent in LiCl-EDTA extracts of cells. Protein k (Mr, 58,000) was extracted from cell envelopes with 2% Triton X-100-10 mM MgCI2 and, in cell envelopes, appeared to be sensitive to trypsin degradation. Proteins with similar properties to those of proteins a to k were found in 10 other H. influenzae b strains, reference strains with serotype a, c, d, e, and f capsules, and 18 of 20 nonencapsulated strains. Their relative molecular weights, however, varied.

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.

Lymphocytes, located within the Peyer's patches, might be involved in the dissemination of enteropathogenic Salmonella typhimurium and Yersinia enterocolitica bacteria. To test this hypothesis, we have investigated the susceptibility of human Band T-cell lines to bacterial adhesion and invasion. The two S. typhimurium strains analyzed were highly invasive, while the two Y. enterocolitica (0:8) strains adhered to the Band T-cell lines but did not enter the cell lines in significant amounts. We hypothesize that the incapability of the Y. enterocolitica (0:8) strains to enter the human Band T-cell lines is most probably due to the bacterial inability to induce the internalization process upon adhesion to both cell lines. Although immortalized Band T-cell lines were used in this study, the results presented suggest the possibility that both cell types could play a role in the dissemination of intracellularly residing S. typhimurium in vivo.

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.