WEDNESDAY, Aug. 29 (HealthDay News) -- One of the worst outbreaks of West Nile virus to ever hit the United States continues to expand, with 66 deaths and 1,590 illnesses reported as of Tuesday, according to the U.S. Centers for Disease Control and Prevention.
Cases have jumped 40 percent nationwide since just last week, the agency added.
Cases have now reached their highest level since the mosquito-borne virus was first found in the United States in 1999, agency officials said in a Wednesday press briefing.
While almost all states have reported at least one case of West Nile illness, over 70 percent of cases have come from six states --- Texas, South Dakota, Mississippi, Oklahoma, Louisiana, and Michigan.
The outbreak has hit hardest in Texas, where nearly half (45 percent) of the total U.S. cases have been reported.
"The number of people reported with West Nile virus continues to rise," said Dr. Lyle Petersen, director of the CDC's Division of Vector-Borne Infectious Diseases. "We have seen this trend in previous West Nile epidemics, so the increase is not unexpected," he added. "In fact, we think the reported numbers will get higher through October."
According to Peterson, of the cases reported so far, 56 percent are what is called neuroinvasive disease, when the virus enters the nervous system causing conditions such as meningitis or encephalitis. The remaining reported cases (44 percent) are non-neuroinvasive.
"These numbers represent a 40 percent increase of last week's report of 1,118 total cases and 41 deaths," Petersen said.
These numbers can be somewhat misleading since most cases of West Nile are non-neuroinvasive and are mostly unreported, the CDC said. That means that the number of unreported cases probably far exceeds reported ones.
Neuroinvasive disease is the most serious for of West Nile infection and these patients usuall
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