Carriage of N. lactamica in a population at high risk of meningococcal disease.

Carriage of Neisseria lactamica among household contacts of meningococcal disease (MCD) cases was investigated during an epidemic in Auckland, New Zealand. The overall carriage rate for N. lactamica was 10.5% (95% CI 7.4-13.5%) with a peak carriage rate in 2-year-olds of 61.5% (95% CI 26.6-88.1%). Factors associated with a significant (P < 0.05) increase in the likelihood of carriage included runny nose, the number of people per bedroom and youth. Genetic analysis of isolates revealed a striking correlation of strains within the same household but a high level of diversity between households, suggesting that household contact is an important factor in acquisition. For household contacts aged less than 5 years, there was a higher rate of carriage amongst those in contact with MCD cases under 8 years old than for contacts of cases aged 8 years and over. It is likely that development of MCD is a reflection of the nature and intensity of the exposure to a virulent strain of N. meningitidis, coupled with an absence of host resistance among those individuals not carrying N. lactamica.