Case-control study of risk factors for human infection with a new zoonoticparamyxovirus, Nipah virus, during a 1998-1999 outbreak of severe encephalitis in Malaysia

An outbreak of encephalitis affecting 265 patients (105 fatally) occurred d uring 1998-1999 in Malaysia and was linked to a new paramyxovirus, Nipah, t hat infected pigs, humans, dogs, and cats. Most patients were pig farmers. Clinically undetected Nipah infection was noted in 10 (6%) of 166 community -farm controls (persons from farms without reported encephalitis patients) and 20 (11%) of 178 case-farm controls (persons from farms with encephaliti s patients). Case patients (persons with Nipah infection) were more likely than community-farm controls to report increased numbers of sick/dying pigs on the farm (59% vs. 24%, P = .001) and were more likely than case-farm co ntrols to perform activities requiring direct contact with pigs (86% vs. 50 %, P = .005), Only 8% of case patients reported no contact with pigs, The o utbreak stopped after pigs in the affected areas were slaughtered and burie d. Direct, close contact with pigs was the primary source of human Nipah in fection, but other sources, such as infected dogs and cats, cannot he exclu ded.