Prevalence of Neisseria meningitidis in family members of patients with meningococcal infection.

The aim of the study was first, to determine the prevalence of Neisseria meningitidis among the family members living with patients suffering from meningococcal infections, and second, to ascertain the distribution among these family members of strains epidemiologically related to those isolated from patients. Forty-two family groups were studied and 135 nasopharyngeal samples were taken from family members living with patients. Twenty family groups were found to contain meningococcal carriers, and of these 20, 13 contained a carrier of the strain that caused the infection (65%). Among the family members who were carriers, the mother and father most frequently yielded the strain which caused the illness. The serotypes most frequently encountered both in patients and carriers were 2 and 8, as well as nontypable strains. The polyacrylamide gel electrophoretic patterns (PAGE) most frequently found were II and IV. A notable feature of the study is the high resistance of the strains to sulphadiazine, since more than 90% of the strains found in patients and more than 75% of those from carriers possessed a minimum inhibitory concentration greater than or equal to 10 micrograms/ml.