Pharyngeal carriage of Neisseria meningitidis and Neisseria lactamica in households with infants within areas with high and low incidences of meningococcal disease

In a household survey in the Faroe Islands, an isolated community with hyperendemic occurrence of meningococcal disease due to serogroup B 15, 1604 persons were examined for pharyngeal carriage of Neisseria meningitidis and N. lactamica. Two areas were chosen having experienced high (HIA), and two having experienced low incidences (LIA) of disease. Living in HIA compared with LIA was associated with higher risk of N. meningitidis B 15 carriage and lower risk of N. lactamica carriage, with odds ratios of 2.7 (95% confidence interval (CI) 1.4-5.1, P = 0.003) and 0.41 (95% CI 0.31-0.53, P less than 0.0001), respectively. In HIA the risk of N. meningitidis carriage was much lower in non-carriers than carriers of N. lactamica, with an odds ratio of 0.19 (95% CI 0.08-0.47, P = 0.0003); in LIA this association (odds ratio 0.51, P = 0.05) was much weaker. Children 0-14 years had substantially higher risk of being carriers of N. meningitidis group B 15 if the mothers were so, with an odds ratio of 11 (95% CI 4-29, P less than 0.0001).