Risk factors for Nipah virus transmission, Port Dickson, Negeri Sembilan, Malaysia: Results from a hospital-based case-control study

A hospital-based case-control study of viral encephalitis was carried out at Port Dickson Hospital, in the state of Negeri Sembilan, Malaysia. Between March and May 1999, 69 clinically diagnosed viral encephalitis cases and 31 controls were interviewed. Job histories on pig farming activities were assessed by a group of epidemiologists and veterinary surgeons. Results show that among clinical cases of viral encephalitis, 52 (75.4%) cases were diagnosed to have Nipah virus infection based on positive serology for antibodies to the cross-reacting Hendra virus antigen. The Nipah virus encephalitis was significantly associated with a history of working in pig farms (p < 0.001, OR = 196.0, 95% CI = 20.4 - 4741.6), history of contact with animals (p < 0.001, OR = 38.3, 95% CI = 8.2 - 209.0) and with history of direct contact with pigs (p = 0.002, OR = 34.4, 95% CI = 2.6 - 1,024.4). The Nipah virus infection was also significantly associated with history of feeding/cleaning pigs (p < 0.001, OR = 102, 95% CI = 11.9 - 2,271.5). These results provide evidence that involvement in pig farming activities is significantly associated with the risk of getting Nipah virus infection. They are potential risk factors for Nipah virus transmission in the major pig-producing area of Bukit Pelandok, Port Dickson Negeri Sembilan.