OBJECTIVE: To describe an outbreak of meningococcal meningitis and the impact of rifampicin chemoprophylaxis on secondary attack rates among Aboriginal people in central Australia.

DESIGN: Prospective study of patients admitted to hospital between September 1987 and May 1991.

SETTING: The Alice Springs Health Region of the Northern Territory and the Anangu Pitjantjatjara Lands of South Australia, covering a population of 13,228 Aboriginal people.

SUBJECTS: Patients admitted to the Alice Springs Hospital with clinical signs or autopsy findings of meningococcal disease. Rifampicin chemoprophylaxis was given to close contacts of all cases. Mencevax AC vaccine was offered to children aged 1 to 15 years in the Region.

MAIN OUTCOME MEASURES: Blood or cerebrospinal fluid (CSF) with Neisseria meningitidis, or a positive result of latex agglutination testing on CSF. Positive isolates were serogrouped.

RESULTS: Seventy-seven cases of meningococcal disease were diagnosed in Aboriginal people over four years compared with one to two cases per year previously; of these, 60 were definite, 7 probable and 10 suspected cases. Seventy-six subjects had meningitis, of whom one also had the clinical features of meningococcal septicaemia; one other subject had positive blood cultures with a mild febrile illness without features of meningitis. The annual attack rate of meningococcal disease in the Aboriginal population was 1.6/1000. The relative risk for secondary cases was estimated to be between 0.3 (95% confidence interval [CI], 0.09-0.92) and 0.5 (95% CI, 0.15-1.53). The annual attack rate in the non-Aboriginal population was 0.04/1000.

CONCLUSIONS: The epidemic closely resembled those in sub-Saharan Africa, and in socioeconomically marginalised groups in developed countries. The relative risk for secondary cases was lower than generally reported, and was attributed to chemoprophylaxis for close contacts and the mass vaccination program for children. Until there are major improvements in living conditions, infectious diseases such as those transmitted by airborne droplets will continue to occur in Aboriginal communities.