An attempt at an epidemiological explanation - Epib.nl

Meningococcal disease ill the Netherlands, 1958-1990INTRODUCfIONMeningococcal disease (MD) still poses major health problems in both developingand industrialized countries. Before 1980 the annual incidence of MD in the Netherlandsvaried between 0.7 and 2.0 cases per 100,000 inhabitants, whereas epidemicsthat occurred in 1946 and 1966 were associated with all annual incidence of 9.9 per100,000 and 4.1 per 100,000, respectively." During the 1980s the incidence of MD inthe Netherlands gradually increased and it reached 3.5 per 100,000 inhabitants in1990.Meningococci are classified into serogroups, serotypes and subtypes OD the basis ofantigenic differences in their capsular polysaccharides, class 2/3 outer-membraneproteins (OMPs) and class 1 OMPs, respectively. Studying the serotype and subtypedistribution of meningococci contributes to the understanding of the epidemiology ofMD' The number of monoclonal antibodies used for serosub typing is still growing,thus improving our insight into the spread of MD.' The characterization of thechromosomal genotype of Neisseria meningitidis isolates by multilocus enzymeelectrophoresis is another valu able tool for studying the epidemiology of MD.'Both in Europe and in the Americas, serogroup B is the predominant serogroupcausing MD, followed in freq uency by serogroup C' 7 Currently, no effective vaccineis available for protection against serogroup B MD. The development of such avaccine is primarily focused on class 1 OMPs.69 Experimental vaccines against serogroupB, which to some extent covered the local needs, were tested in Norway, Cubaand Chile. I " 12 The reported efficacy of these vaccines ranged from 51 % to 81%. ITOMP vaccines are to be used for the prevention of serogroup B MD, it becomesessential to monitor the distribution of subtypes over time in order to allow foradaptation of the vaccine to the current circulation of subtypes.Since 1958, meningococcal isolates from blood and/or cerebrospinal fluid (CSF)have been submitted for further classification to the Reference Laboratory fo rBacterial Meningitis (RLBM) in Amsterdam by ahoost all microbiologists in theNetherlands. The strain collection currently comprises of approximately 7000meningococcal isolates. On the basis of this extensive collection, we report thechanging pattern of the serotype and sub type distribution of meningococci in theNetherlands, as determined with the use of monoclonal antibodies against 7 serotypesand 11 subtypes. Our typing results are compared with those obtained with multilocusenzyme electrophoresis in a former survey of strains from patients in the Netherlands13 Special attention is paid to the period 1980-1990, during which the incidenceof MD gradually increased to a subepidemic level. By comparing the results fromtyping in this period with those from the period 1958-1975, we attempt to explain theincreased number of cases. In addition, we describe the shift in the age-distributionand the increase in the recovery of isolates from blood alone - phenomena that wereobserved during ti,e last decade - and discuss tlleir relation to the serogroup andserosubtype distribution.19