Re-emergence of meningococcal carriage on three-year follow-up of a kibbutz population after whole-community chemoprophylaxis.

A long-term study was conducted to determine the rate of re-emergence of throat carriage of meningococci in a semi-closed kibbutz community after the administration of chemoprophylaxis to all its members. Serotype B:4 was selected as marker organism since it was isolated from a fatal case and was the most frequently occurring strain (80%) among serogroup B isolates, which themselves comprised 54% of all meningococci. The carriage rate among Israeli residents (volunteer workers were analyzed separately) before treatment was 6.6% (49/748) overall, with 4.3% group B strains. Three weeks after treatment, in most cases with rifampicin (whereby three persistently positive persons were retreated with minocycline), no meningococci were recovered. Six months later, 1.9% of a population sample aged < or = 30 years were positive, while before treatment and one and three years later, 9.4%, 8.6% and 4.6% respectively were positive in this age group. Serotype B:4 comprised 81.3% of group B strains before prophylaxis, 5.3% after one year, and 28.6% after three years, thus possibly re-establishing itself as the single dominant serotype. The marked suppression of carriage after mass chemoprophylaxis appeared to last at least six months, with the meningococcal population being re-established within a year.