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West Nile Virus Outbreak on Track to Be Deadliest Ever

By Roy Maurer  9/14/2012

U.S. health officials said they’re convinced this will be the deadliest year for West Nile virus deaths and severe illnesses since the disease first hit America’s shores in 1999.

The numbers for West Nile virus cases continue to rise, up 35 percent since Sept. 4, 2012. The silver lining is that the outbreak may have peaked in late August, said Lyle Petersen, director of the Centers for Disease Control and Prevention’s (CDC) division of vector-borne infectious disease, in his Sept. 11, 2012, weekly West Nile virus update.

We’re hopeful that the worst of the outbreak is behind us,” Petersen said.

As of Sept. 11, 2012, 48 states have reported West Nile virus infections in people, birds or mosquitoes. There have been 2,636 infections reported in people thus far in 2012; 53 percent of the cases were the most severe form of the disease, including 118 deaths, according to the CDC. (Read “West Nile Virus Spreading Across U.S. for information about communicating with employees about and protecting them from West Nile.)

In addition to the 1,405 cases (53 percent) that were classified as neuroinvasive disease (such as meningitis or encephalitis), 1,231 cases (47 percent) were classified as non-neuroinvasive disease.

Two-thirds of the cases have been reported from six states (Texas, Louisiana, South Dakota, Mississippi, Michigan and Oklahoma), and 40 percent of all cases have been reported from Texas.

Case numbers are expected to rise through October because of the time lag between the onset of symptoms, doctor visits and reporting to authorities. People who were infected two to three weeks ago are just getting their cases reported now, the CDC noted.

“If this year turns out to have the most neuroinvasive cases of any year, which is what we’re on track for, we expect this year to have the largest number of deaths of any year,” Petersen said.

The worst year for the mosquito-borne disease was 2002, which saw nearly 3,000 severe cases and 284 deaths, according to the CDC.

This year’s epidemic has created a huge demand for West Nile test kits, leading to a temporary shortage of kits, the CDC reported.

About one in five of the people who become infected with West Nile virus have symptoms such as fever, headache, body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms can last for as short as a few days, though even healthy people have become sick for several weeks, according to the CDC.

About one in 150 people infected will develop severe illness. The severe symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and neurological effects may be permanent, according to the CDC.

Approximately 80 percent of people who are infected with the disease will not show any symptoms at all.

People typically develop symptoms between three and 14 days after they are bitten by the infected mosquito.

West Nile virus was first diagnosed in Uganda in 1937, but no cases were reported in the U.S. until 1999 in New York City. The virus gradually spread across the country.

Roy Maurer is an online editor/manager for SHRM.

Related Article:

West Nile Virus Spreading Across U.S., SHRM Online Safety & Security Discipline, August 2012

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