Outbreak of Nipah-virus infection among abattoir workers in Singapore

Background In March 1999, an outbreak of encephalitis and pneumonia occurre d in workers at an abattoir in Singapore. We describe the clinical presenta tion and the results of investigations in these patients. Methods Clinical and laboratory data were collected by systemic review of t he case records. Serum and cerebrospinal fluid (CSF) samples were tested fo r IgM antibodies to Nipah virus with an IgM capture ELISA, Reverse-transcri ptase PCR was done on the CSF and tissue samples from one patient who died. Findings Eleven patients were confirmed to have acute Nipah-virus infection based on raised IgM in serum. Nipah virus was identified by reverse-transc riptase PCR in the CSF and tissue of the patient who died. The patients wer e all men, with a median age of 44 years. The commonest presenting symptoms were fever, headache, and drowsiness. Eight patients presented with signs of encephalitis (decreased level of consciousness or focal neurological sig ns). Three patients presented with atypical pneumonia, but one later develo ped hallucinations and had evidence of encephalitis on CSF examination. Abn ormal laboratory findings included a low lymphocyte count (nine patients), low platelet count, low serum sodium, and high aspartate aminostransferase concentration (each observed in five patients). The CSF protein was high in eight patients and white-blood-cell count was high in seven. Chest radiogr aphy showed mild interstitial shadowing in eight patients. Magnetic resonan ce imaging (MRI) showed focal areas of increased signal intensity in the co rtical white marker in all eight patients who were scanned. The nine patien ts with encephalitis received empirical treatment with intravenous aciclovi r and eight survived. Interpretation Infection with Nipah virus caused an encephalitis illness wi th characteristic focal areas of increased intensity seen on MRI, Lung invo lvement was also common, acid the disease may present as an atypical pneumo nia.