Carriage of a new epidemic strain of Neisseria meningitidis and its relationship with the incidence of meningococcal disease in Galicia, Spain

In Galicia, Spain, a dramatic increase in the incidence of meningococcal di sease was seen in the 1995-6. The annual incidence rose to 11 per 10(5) inh abitants, and 80% of identified strains were C:2b:P1.2,5. This led to the i mplementation of an intensive A+C vaccination campaign for the population a ged 18 months to 19 years. During this campaign the prevalence of carriage in areas with high and low incidence was studied. Nasopharyngeal swabs were taken from 9796 subjects immediately before the administration of meningoc occal vaccine, plated onto Thayer-Martin plates, incubated and sent for ana lysis to the Reference Laboratory for Neisseria in Spain. The prevalence of the C:2b:P1.2,5 strains was 0.6 % (95 % Cl 0.29-0.88) in the high incidenc e area, and 0.41% (95 % Cl 0.00-1.04) in the low incidence area, and that o f serogroup C (all strains) 1.36 % (95 % Cl 0.80-1.80) and 0.89 % (95 % Cl 0.09-1.69) respectively. The prevalence of N. meningitidis (all strains) wa s almost the same in both areas (8 %). Carriers of the epidemic strain were not found in the 2-4 year age group, that most affected by the disease. Our data showed a wide distribution but a low carriage rate of the epidemic strain C:2b:P1.2,5 in the high and low disease incidence areas studied; th e difference in the carriage rates between the two areas was not statistica lly significant.