West Nile Cost United States Nearly $800 Million in 14 Years

Marcia Frellick

February 10, 2014

West Nile virus (WNV) has cost the United States $778 million in hospitalizations and lost productivity in the 14 years since it was first detected in the Western Hemisphere, new research shows.

J. Erin Staples, MD, PhD, a medical epidemiologist at the Centers for Disease Control and Prevention (CDC) in Fort Collins, Colorado, and colleagues studied WNV's economic effect from 1999 to 2012, publishing their findings online February 10 in the American Journal of Tropical Medicine and Hygiene.

"Only with accurate figures can public health, academic, and industry officials determine the cost effectiveness of local mosquito control measures or of developing new drugs and vaccines," Dr. Staples said in a news release.

Previous studies likely have underestimated the costs of the disease spread to humans by mosquitoes because they focused on the initial illness, the authors write.

In the current study, the researchers started with cost of initial hospitalization for 80 patients during a 2003 outbreak in Colorado. For 38 of these patients, they then calculated costs of additional physician visits, medications, and lost work and school time during the next 5 years. They extrapolated those costs to the total number of hospitalized cases of WNV disease reported to CDC since 1999.

Those findings suggest an annual burden of $56 million in the United States. However, the annual cost varies widely, as the number of WNV disease cases has ranged from a low of 21 cases in 2000 to 9862 cases in 2003.

The 37,088 WNV disease cases reported to the CDC from 1999 through 2012 included more than 16,000 patients with neurologic disease, more than 18,000 patients who were hospitalized, and more than 1500 deaths. Annual outbreaks have continued to occur across the United States.

About 1 in 5 people infected will develop a fever with symptoms such as headache and joint pain, but about 1 in 150 develop a serious nervous system illness, such as encephalitis or meningitis, that typically requires hospitalization.

"While patients with meningitis had shorter hospital stays than others with neurological syndromes, they were also younger and more likely to miss work, which translated to a higher economic cost in lost productivity," Dr. Staples said in the news release. "Encephalitis patients tended to be older, with many of them retired, so the cost associated with lost productivity was lower."

Patients hospitalized with acute flaccid paralysis, a partial- to whole-body paralysis, had the largest initial and long-term costs (median, $25,000 and $22,000, respectively).

Short- and long-term costs for people hospitalized with WNV disease varied widely by syndrome encountered. This is the first published cost analysis for the 4 "clinical syndromes" of the disease, fever, meningitis, encephalitis, and acute flaccid paralysis, the authors write.

In an accompanying editorial, Alan D. T. Barrett, PhD, from the Department of Pathology, Sealy Center for Vaccine Development, Center for Biodefense and Emerging Infectious Diseases, Center for Tropical Diseases, and Institute for Human Infections and Immunity, University of Texas Medical Branch, Galveston, asks whether results from this subset can be generalized to the US population.

"[T]he question arises can data obtained in Colorado be extrapolated to other states as population demographics vary by state and geographic locations of WNV cases differ each year? Furthermore, the authors make a major assumption that the 38 patients in the five-year follow-up period are representative of the entire United States. Overall, this makes averaging costs difficult because some states have had few cases over the last 15 years and other states have had cases most years."

Although studies such as this one are important in helping guide public health decisions, "there is a need for more studies of economic burden caused by WNV infection that evaluate populations in other states, costs involved in multi-year long-term follow-up of patients with neurologic sequelae, and studies with larger sample sizes, although it is recognized that such studies are difficult to conduct," he writes.

The authors and Dr. Barrett have disclosed no relevant financial relationships.

Am J Tropical Med Hygiene. Published online February 10, 2014. Article full text, Editorial full text

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