West Nile virus disease: a descriptive study of 228 patients hospitalized in a 4-county region of Colorado in 2003.

BACKGROUND: Risk factors for complications of West Nile virus disease and prognosis in hospitalized patients are incompletely understood. METHODS: Demographic characteristics and data regarding potential risk factors, hospitalization, and dispositions were abstracted from medical records for residents of 4 Colorado counties who were hospitalized in 2003 with West Nile virus disease. Univariate and multivariate analyses were used to identify factors associated with West Nile encephalitis (WNE), limb weakness, or death by comparing factors among persons with the outcome of interest with factors among those without the outcome of interest. RESULTS: Medical records of 221 patients were reviewed; 103 had West Nile meningitis, 65 had WNE, and 53 had West Nile fever. Respiratory failure, limb weakness, and cardiac arrhythmia occurred in all groups, with significantly more cases of each in the WNE group. Age, alcohol abuse, and diabetes were associated with WNE. Age and WNE were associated with limb weakness. The mortality rate in the WNE group was 18%; age, immunosuppression, requirement of mechanical ventilation, and history of stroke were associated with death. Only 21% of patients with WNE who survived returned to a prehospitalization level of function. The estimated incidence of West Nile fever cases that required hospitalization was 6.0 cases per 100,000 persons; West Nile fever was associated with arrhythmia, limb weakness, and respiratory failure. CONCLUSIONS: Persons with diabetes and a reported history of alcohol abuse and older persons appear to be at increased risk of developing WNE. Patients with WNE who have a history of stroke, who require mechanical ventilation, or who are immunosuppressed appear to be more likely to die. Respiratory failure, limb weakness, and arrhythmia occurred in all 3 categories, but there were significantly more cases of all in the WNE group.

Delayed mortality in a cohort of persons hospitalized with West Nile virus disease in Colorado in 2003.

Most mortality associated with West Nile virus (WNV) disease occurs during the acute or early convalescent phases of illness. However, some reports suggest mortality may be elevated for months or longer after acute illness. The objective of this study was to assess the survival of a cohort of patients hospitalized with WNV disease in Colorado in 2003 up to 4 years after illness onset. We calculated age-adjusted standardized mortality ratios (SMRs) to evaluate excess mortality, evaluated reported causes of death in those who died, and analyzed potential covariates of delayed mortality. By 1 year after illness onset, 4% of the 201 patients had died (SMR, 2.7; 95% confidence interval [CI], 1.3-5.2), and 12% had died by 4 years after onset (SMR, 2.0; 95% CI, 1.3-3.0). Among those who had died, the most common immediate and contributory causes of death included pulmonary disease and cardiovascular disease; cancer, hepatic disease, and renal disease were mentioned less frequently. In multivariate analysis, age (hazard ratio [HR], 2.0 per 10-year increase; 95% CI, 1.4-2.7), autoimmune disease (HR, 3.0; 95% CI, 1.1-7.9), ever-use of tobacco (HR, 3.0; 95% CI, 1.3-7.0), encephalitis during acute WNV illness (HR, 2.6; 95% CI, 1.1-6.4), and endotracheal intubation during acute illness (HR 4.8; 95% CI, 1.9-12.1) were found to be independently associated with mortality. Our finding of an approximate twofold increase in mortality for up to 3 years after acute illness reinforces the need for prevention measures against WNV infection among at-risk groups to reduce acute as well as longer-term adverse outcomes.

West Nile Virus-associated flaccid paralysis outcome.

We report 1-year follow-up data from a longitudinal prospective cohort study of patients with West Nile virus-associated paralysis. As in the 4-month follow-up, a variety of recovery patterns were observed, but persistent weakness was frequent. Respiratory involvement was associated with considerable illness and death.

Virology, pathology, and clinical manifestations of West Nile virus disease.

West Nile virus (WNV) causes epidemics of febrile illness, meningitis, encephalitis, and flaccid paralysis. Since it was first detected in New York City in 1999, and through 2004, >16,000 WNV disease cases have been reported in the United States. Over the past 5 years, research on WNV disease has expanded rapidly. This review highlights new information regarding the virology, clinical manifestations, and pathology of WNV disease, which will provide a new platform for further research into diagnosis, treatment, and possible prevention of WNV through vaccination.

West Nile virus-associated flaccid paralysis.

The causes and frequency of acute paralysis and respiratory failure with West Nile virus (WNV) infection are incompletely understood. During the summer and fall of 2003, we conducted a prospective, population-based study among residents of a 3-county area in Colorado, United States, with developing WNV-associated paralysis. Thirty-two patients with developing paralysis and acute WNV infection were identified. Causes included a poliomyelitislike syndrome in 27 (84%) patients and a Guillain-Barré-like syndrome in 4 (13%); 1 had brachial plexus involvement alone. The incidence of poliomyelitislike syndrome was 3.7/100,000. Twelve patients (38%), including 1 with Guillain-Barré-like syndrome, had acute respiratory failure that required endotracheal intubation. At 4 months, 3 patients with respiratory failure died, 2 remained intubated, 25 showed various degrees of improvement, and 2 were lost to followup. A poliomyelitislike syndrome likely involving spinal anterior horn cells is the most common mechanism of WNV-associated paralysis and is associated with significant short- and long-term illness and death.

Post-infectious encephalomyelitis associated with St. Louis encephalitis virus infection.

Neurologic illness associated with acute St. Louis encephalitis, West Nile, and Japanese encephalitis virus infection includes acute aseptic meningitis, encephalomyelitis, and a poliomyelitis-like syndrome. Few post-infectious immune-mediated neurologic events associated with flaviviral infection have been reported. The authors report on a woman with apparent post-infectious encephalomyelitis associated with recent St. Louis encephalitis virus infection, suggesting that neurologic illness from flaviviruses may also be seen in the post-infectious period following mild clinical illness.