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We tested two sets of primers derived from the dhps gene of Neisseria meningitidis for the amplification of meningococcal DNA by PCR. Both the NM1-NM6 primers and the NM3-NM6 primers amplified dhps DNA from all of the meningococci included in the study, resulting, in most cases, in amplicons of 0.70 and 0.23 kb, respectively. Also, dhps DNAs of N. gonorrhoeae and some commensals were amplified but Haemophilus influenzae, Streptococcus pneumoniae, and Escherichia coli DNAs were not. By PCR amplicon restriction endonuclease analysis (AREA) of the larger amplicon, we could differentiate between individual strains of N. meningitidis. Following two cases of meningococcal disease, we used PCR AREA to identify healthy contacts carrying the disease-causing strain. We conclude that PCR AREA is a useful method for meningococcal strain differentiation and that it has potential as a method for studying the spread of a disease-causing strain in an affected population. The method is quicker and easier to perform and interpret than chromosomal DNA fingerprinting.

In Norway, the use of chemoprophylaxis after cases of meningococcal disease is not recommended. Instead, household members less than 15 years are treated with penicillin for 7 days. Failures of this treatment have been reported. We therefore used DNA fingerprinting to identify the disease-causing strain in healthy contacts combined with selective rifampicin prophylaxis to these carriers to prevent secondary cases. During a 2-year period (1987-89) there were 13 cases of meningococcal disease in the County of Telemark (165000 inhabitants). 65 (14.7%) out of 441 contacts to these 13 patients harbored meningococci in their throat; 16 (3.6%) carried the disease-causing strain. Only 1 carrier fulfilled the criteria for being treated with penicillin; 8 were adults and the remaining 7 were not household members. No secondary cases of meningococcal disease occurred during the study period or the following 12 months. During the 4-year period (1984-87) preceding the study period there were 39 cases of meningococcal disease in Telemark; 7 of them were index cases for 12 bacteriologically verified and 4 clinically suspected secondary cases of meningococcal disease. We conclude that selective prophylaxis with rifampicin seems to be more efficient that penicillin treatment of household members less than 15 to prevent secondary cases of meningococcal disease.

Rapid diagnosis of meningococcal disease followed by early treatment is essential. However, culture of blood or cerebrospinal fluid (CSF) may be unsuccessful because antibiotic treatment is often started before adequate specimens are collected, and because bacteria may die during transportation to the laboratory. We have used the polymerase chain reaction (PCR) to detect meningococcal DNA in a culture-negative CSF of a 15-year-old girl with meningococcal disease. Two oligonucleotides flanking the dihydropteroate synthase gene (dhps) of Neisseria meningitidis were used as primers. The PCR reaction is a rapid technique for the early detection of meningococcal meningitis, and also when culture is negative.

By cloning studies and complementation experiments, the sulfonamide resistance gene of a serogroup B and serotype 15 (B:15) strain of Neisseria meningitidis was localized to a 1.2-kb chromosomal SspI fragment expressing a drug-resistant dihydropteroate synthase. The fragment hybridized to DNA from both resistant and susceptible strains, suggesting that the resistance gene is a variant of the normal gene for dihydropteroate synthase.