The only states that have not reported cases are Alaska and Hawaii, he said.
"Based on current reports, we think the number of cases may come close to, or even exceed, the total number reported in the epidemic years of 2002 and 2003, when more than 3,000 cases of neuroinvasive disease and more than 260 deaths were reported each year," Petersen said.
The reasons for a major outbreak this year aren't clear, Petersen said. The drought in Texas may have played a role, but there were probably other factors as well, he added.
The best way to avoid the virus is to wear insect repellant and support local programs to eradicate misquotes, Petersen said.
There is currently no treatment for West Nile virus and no vaccine to prevent it, he added.
Speaking at the press conference, Dr. David L. Lakey, Commissioner of the Texas Department of State Health Services said that, "As I look at the data, I am not convinced that we have peaked."
Since last week, there have been 197 new cases and 10 more deaths in Texas, Lakey said. "Those numbers will continue to go up," he added.
Generally speaking, 80 percent of people who are infected with West Nile virus develop no or few symptoms, while 20 percent develop mild symptoms such as headache, joint pain, fever, skin rash and swollen lymph glands.
Less than 1 percent will develop neurological illnesses, such as encephalitis or meningitis, and develop paralysis or cognitive difficulties that can last for years, if not for life.
People older than 50 and those with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease and organ transplants, are at greater risk for serious illness, according to the CDC.
There are no specific treatments for West Nile virus; the greatest risk for infection with West Nile virus typica
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