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[Meningococcal disease in Spain, 1990-1997. Change in its epidemiological pattern].

BACKGROUND
In Spain, the presentation of meningococcal disease in the 1980s was closely linked to the predominance of N. Meningitidis serogroup B. This situation changed at the beginning of the 1990s, observing a growing trend of serogroup C strains in the isolation procedures carried out in some areas of the country, together with an increase in the incidence of the disease starting in the 1995-1996 season. The purpose of this study is to characterise the epidemiological pattern of meningococcal disease in Spain during the 1990-97 season and, in particular, where the disease was caused by the phenotype C:2b:P1.2.5 in this period of etiological change.


METHODS
Retrospective study of the cases of meningococcal disease in Spain, with the exception of the Autonomous Communities of Andalusia, Cantabria, Madrid, Basque Country and Valencia, between 1990-1997. The epidemiological data were obtained from the Compulsory Disease Reporting system, through individualised notification of cases, and the microbiological data from the Meningococcus Reference Laboratory of the National Microbiology Centre.


RESULTS
The incidence of meningococcal disease in the period studied, 1990-1997, was 3.81 x 10 - 6 person-years, increasing by 0.1851 cases per 100,000 inhabitants per year. Starting in 1995, the incidence caused by serogroup C practically tripled with respect to the preceding period, with a rate of incidence in 1997 of 2 cases per 100,000 inhabitants. This increase was to a large extent due to the emergence of the phenotype C:2b:P1.2,5, which in that same year registered an incidence of 1 case per 100,000 inhabitants. The increase in incidence affected all age groups, but was particularly significant in the 5-19 year-old group (annual rate of growth: 13.3%; P < 0.001). It was also found that there was an increase in the number of outbreaks reported and cases associated to them. The overall mortality rate was 7.7% (95% confidence interval: 7.0-8.4), and the mortality associated with the phenotype C:2b:P1.2.5 was significantly higher than that of the serogroup B chosen as reference (odds ratio: 1.69; 95% CI: 1.05-2.71), following adjustment for age, sex, clinical form and year.


CONCLUSIONS
The pattern of meningococcal disease in the territory studied, during 1990-1997, was characterised by an increase in the incidence of serogroup C, particularly the emerging phenotype C:2b:P1.2,5. Together with this increase, a displacement of the incidence to higher age groups was observed, together with a tendency towards temporospatial aggregations of cases and an increase in the mortality associated with the new phenotype. This pattern is characteristic of epidemic situations of meningococcal disease caused by serogroup C.