Hospitalizations due to the West Nile virus have cost the United States' health-care system almost $800 million in the past 14 years, showing that the costs have been underestimated, according to a team from the Centers for Disease Control and Prevention.

The findings about the cost and effects of the West Nile virus — spread to humans by infected mosquitoes — were published online today in the American Journal of Tropical Medicine and Hygiene.

Reports of serious and sometimes fatal infections first emerged in 1999, when the term "West Nile" became well-known.

Since then, more than 37,000 cases have been reported to the CDC, likely an underestimate of the entire number, according to researchers.

Approximately one in five infected people will develop a fever, headaches and joint pain.

But out of 150 cases, about one of those will go on to develop “a serious nervous system illness such as encephalitis or meningitis that typically requires hospitalization,” according to the report.

But the long-term needs of those infected with the virus are not well-known, according to the report.

"We believe that previous costs associated with West Nile virus disease have been underestimated because they've predominantly focused on the costs of the initial illness," said J. Erin Staples, lead author of the study and a medical epidemiologist with the CDC in Fort Collins, Colorado.

"Many hospitalized patients will incur additional medical and indirect costs, and these need to be figured into the burden of WNV disease. 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."

The study examined the costs of the hospitalization as well as long-term costs over the next five years, including follow-up appointments with family physicians.

It also included the time in which the infected patient missed school or work, adding to the amount of money lost and added loss in productivity.

Costs underestimated

The determined cost on the U.S. was determined by the team, using information on the hospitalization of 80 patients during an outbreak in Colorado in 2003.

Researchers calculated the costs of additional medical care and missed work over the next five years following infection for a subset of patients, and then estimated the total cost toward the country by extrapolating and figuring the annual cost somewhere around $56 million.

The study was the first to look at the costs for four specific syndromes connected to the infection.

"We broke down costs by clinical syndrome and were surprised by what we found. 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," Staples said.

"Encephalitis patients tended to be older, with many of them retired, so the cost associated with lost productivity was lower."

Alan D. T. Barrett, a tropical viral disease specialist at the University of Texas Medical Branch, said that studies like this are critical in understanding “cost-effectiveness of prevention and therapeutic countermeasures.”

"There are a number of candidate vaccines and antiviral drugs in development, and the figures for economic burden reported in this paper will aid policy makers and pharma to assess the economics of vaccine and drug development," he wrote.