Epidemiology and clinical investigation of West Nile Virus encephalitis in Houston, Texas
Kristy O. Murray
MetadataShow full item record
In 2002, West Nile virus (WNV) appeared in Houston. Retrospective medical chart reviews were completed for 172 WNV cases hospitalized in the Houston area between 2002 and 2004; 113 had encephalitis (including 17 fatal cases), 47 had meningitis, and 12 were uncomplicated fever cases. Risk factors associated with progression from encephalitis to death were renal insufficiency, requiring intubation and mechanical ventilation, presence of myoclonis or tremors, and loss of consciousness. Pleocytosis in the cerebrospinal fluid was considered protective. A nested case-control study identified advanced age (odds ratio [OR]=1.1; p<0.001), history of hypertension, including those cases taking drugs which can induce hypertension (OR=2.9; p=0.012), and history of cardiovascular disease (OR=3.5; p=0.061) as independent risk factors for developing encephalitis from WNV infection. After adjusting for age, race/ethnicity (being black) (OR=12.0; p<0.001), chronic renal disease (OR=10.6; p<0.001), being positive for hepatitis C virus (OR=23.1; p=0.0013), and immunosuppression (OR=3.9; p=0.033) were identified as risk factors for death. Patient interviews were used to examine demographics and medical histories; age of 55 years or greater (Odds Ratio [OR]=5.7; 95% CI 1.8, 17.9; p=0.003) and history of hypertension (OR=3.7; 95% CI 1.2, 12.0; p=0.027) were independently associated with encephalitis, supporting the findings from the nested case-control study. At three years post-onset, 42% of patients were still reporting symptoms related to their WNV illness. Objective measurements revealed significant differences in both the mini-mental status exam and Barthel Index between encephalitis patients and those who presented with meningitis or fever. New onset depression was reported by 31% of cases, with 75% having CES-D scores indicative of mild to severe depression. Serial blood draws were tested by ELISA, and persistence of anti-WNV IgM antibodies were found in 24% and 18.4% of patients approximately two and three years post-onset, respectively. Persistence of IgM from previous transmission seasons could potentially result in false interpretation of positive test results. This study provides us with a better understanding of the clinical aspects of a virus that is likely to continue to circulate in the United States, and allows us to identify populations at risk for encephalitis and death.