Meningococcal disease in Malawi: studies on the genetic relatedness of the bacteria.

Seventy-seven meningococci, isolated from patients and carriers during a large epidemic of meningococcal meningitis in Malawi, were characterized in terms of antimicrobial susceptibility, plasmid content and multi-locus enzyme electrophoresis (MLEE). All the isolates were sensitive to chloramphenicol but six had high enough minimum inhibitory concentrations of penicillin (> or = 2 mg/litre) to render them clinically resistant. Only one isolate was sensitive to sulphonamides but all the isolates were sensitive to rifampicin and ciprofloxacin, two drugs that would be suitable alternatives in prophylaxis. None of the isolates carried plasmids. MLEE indicated that 32 (80%) of the cerebrospinal fluid isolates and 22 (69%) of those from carriers were closely related genetically (in two electropherotypes that differed at only one allele). The Malawian group A meningococci differed from three Ethiopian isolates by two or three alleles, indicating that direct spread from the sub-Saharan meningitis belt to Malawi was unlikely.