Background: A) To ascertain the rate of carriers and the Types of Neisseria Meningitidis circulating in the population resident in the health jurisdiction of Gran Canaria. B) to ascertain the pattern of distribution of such carriers.
Methods: A descriptive transversal design was made, with a random sampling in multiple stages and by conglomerates. A minimum sample size was determined at 707 individuals for an expected prevalence of 8.6%, with a rate of reliability of 95.6% and a precision of 0.02. Assuming that 15% if the individuals would not be willing to co-operate, the sample size was increased to 831 individuals, distributed in each conglomerate in proportion to the existing population. This size was distributed in turn into four groups by age and sex, in proportion to their significance in each basic health care zone selected at random. The individuals in the sample were identified from among those who attended the blood extraction units, and after they had passed the criteria of exclusion, their co-operation was requested as volunteers in the study. If they accepted, a questionnaire was filled out with a number of variables of epidemiological interest and a pharyngeal smear was taken. Since the Primary Care units were selected on a simple random basis, and the same method was used to select the individuals within the units, the estimate of the prevalence was made by means of an unbiased estimator.
Results: A total of 828 samples were obtained, that is, 99.6% of the number foreseen. With the exception of three, all of the individuals selected participated voluntarily in the study, a circumstance rendering it highly representative. All of the strains obtained corresponded to N. Meningitidis Serogroup B, except for one identified as N. Meningitidis Serogroup C Sero/Subtype 4:P1.2,5. The strains of N. Meningitidis serogroup B identified corresponded to 25 different sero-subtypes. The prevalence determined after having studied the sample was 6.45%, the variance = 0.0275 and the standard error = 1.66. We can conclude with a 95% degree of reliability that the prevalence of carriers of N. Meningitidis in the Gran Canaria health jurisdiction is estimated to be between 3.2% and 9.7%.
Conclusions: A clear predominance of N. Meningitidis serogroup B strains among carriers has been verified. There are no statistically significant differences in the prevalence observed among the different age groups nor between sexes.