Outbreak of meningococcal disease caused by PorA-deficient meningococci.

An outbreak of 7 cases of group C meningococcal disease occurred during the last week of July and the first week of August 2001 in the southwestern part of The Netherlands. Characterization of the 7 patients' isolates by various typing methods showed that the isolates were identical, except for the expression of PorA. Isolates from 5 patients were PorA deficient. These results show that transmission of PorA-deficient meningococci occurs and that PorA-deficient meningococci can cause invasive disease. PorA-based meningococcal vaccines may provide limited protection.