In Malaysia and Singapore, the majority of affected cases were men, reflecting the occupational exposure. The incubation period was less than 2 weeks in 90% of cases and the majority of infected individuals (55%-85%) developed symptomatic illness. Central nervous system disease was typically preceded by a 3- to 4-day prodrome of fever, nausea, myalgia, and dizziness. The initial presenting features, based on a series of 94 total cases from the initial and subsequent outbreaks in Malaysia, included fever (87%), headache (65%), dizziness (36%), and vomiting (27%).57,58Neurological signs included reduced tendon reflexes (56%), segmental myoclonus (32%), nuchal rigidity (28%), and seizures (23%) and cerebellar abnormalities (9%). A compilation of 92 cases from outbreaks between 2001 and 2004 in Bangladesh59found the most common clinical characteristics to be fever (100%), altered mental status (90%), headache (73%), respiratory difficulty (69%), severe weakness (67%), and seizures (23%). Overall mortality was 73%. In the Malaysian series, common laboratory abnormalities included a CSF pleocytosis (75%-85%) with mean cell counts of approximately 40/mm3, elevated protein level (mean, 69 mg/dL), and a normal glucose level.57,58The frequency of CSF pleocytosis appears to be variable, as another series found that only 1 of 6 laboratory-confirmed cases had more than 9 cells/mm3.59Computed tomographic scan was usually normal,57,58but MRI was abnormal in almost all patients examined. The most common finding was multiple small (2- to 7-mm) areas of increased T2 and fluid-attenuated inversion recovery signal in the subcortical and deep white matter, usually without mass effect or edema (Figure 4).