The CDC has reported that the number of West Nile virus disease cases has risen dramatically in recent weeks, indicating one of the largest West Nile virus outbreaks ever seen in the United States.
As of Tuesday, 1,118 human cases of West Nile disease, including 41 deaths, have been reported to the CDC, Lyle Petersen, MD, MPH, director of the division of vector-borne infectious diseases at the CDC, said during a media briefing today. Of the 1,118 cases, 629 were classified as neuroinvasive disease, such as meningitis or encephalitis.
“In comparison, there were only 25 cases of West Nile virus disease reported to the CDC 1 month ago,” Petersen said. “The cases and deaths identified thus far in 2012 are the highest number of West Nile virus cases reported to the CDC since the virus was first detected in the United States in 1999.”
Forty-seven states have reported West Nile virus infections in humans, birds or mosquitoes. The only states not reporting activity are Alaska, Hawaii and Vermont. Of the 47 states, 38 had human cases of the disease. Approximately 75% of the cases were reported from five states: Texas, Mississippi, Louisiana, South Dakota and Oklahoma, Petersen said. About half of those cases are from Texas.
“As of right now, we have 586 cases statewide, including 21 deaths,” David Lakey, MD, commissioner of the Texas Department of State Health Services, said during the briefing. “Prior to this, our worst season was 2003, when we had 439 cases of neuroinvasive disease and 40 deaths overall, statewide.”
Petersen said 242 potentially viremic blood donors were also reported in 26 states compared with 25 viremic blood donors reported just 1 month ago. All blood donors are screened for West Nile virus.
“By identifying these patients and deferring them from giving blood, we are taking an important step in preventing the spread of the virus and protecting the US blood supply,” Petersen said.
The West Nile virus epidemic usually occurs in mid-August, but because it takes several weeks for people to be diagnosed and reported, many more cases are expected to occur, he said, adding that the risk for West Nile virus infection will probably occur through the end of September.
It is also unclear why there is more West Nile activity in 2012 than has been in recent years. Factors that affect West Nile activity include the weather, the number of birds that have the virus and the number of mosquitoes that spread the virus. In addition, the mild winter, early spring and hot summer in many parts of the country may have fostered conditions favorable to the spread of the virus.
Petersen said it is important for people to continue taking steps to protect themselves against mosquito bites by using insect repellant, wearing long sleeves outdoors, installing screens on doors and windows, using air conditioning and emptying standing water from items outside of the home.
Check back with www.healio.com/Infectious-Disease for updates on the West Nile virus in the United States.