The recent West Nile virus outbreak in the U.S. is said to be one of the worst since the virus first appeared in the country in 1999, according to new figures from the Centers for Disease Control and Prevention.

The CDC said a total of 1,118 cases, including 41 deaths, had been reported as of Aug. 21. The figure, which reflects reports from 38 states, is the highest on record in the U.S., which has seen three times the usual number of cases being reported for this time of year, officials said.

"The peak of West Nile virus epidemics usually occur in mid-August, but it takes a couple of weeks for people to get sick, go to the doctor and get reported," Dr. Lyle Petersen, the director of the CDC's Vector-Borne Infectious Disease Division, told the media. "Thus we expect many more cases to occur."

While the reason for the high number of cases this year is said to be unclear, Petersen said that unusually warm weather could have fostered favorable conditions for the disease's transfer to humans.

According to CNN, about 75% of the cases are in Texas, Mississippi, Louisiana, South Dakota and Oklahoma. In recent months, Texas has been at the epicenter of the outbreak, with 586 confirmed cases and 21 deaths, according to the Texas Department of State Health Services.

As most people infected with the West Nile virus show no symptoms, officials estimate that more than 94,000 people in the United States have been infected with the virus this year. It's likely that about 98 percent of cases of West Nile fever are not reported, the CDC said.

"The problem is even larger ... than the already notably larger problem of neuroinvasive disease," William Schaffner, chairman of the department of preventive medicine at Vanderbilt University, told Live Science. The impact of unreported cases is a factor in the decision to call the current West Nile outbreak an emergency, as Dallas did, Schaffner said.

Here are some ways you can help prevent the West Nile Virus:

  • Use mosquito repellent with DEET
  • Dress in long pants and long sleeves
  • Be especially careful at dusk and dawn
  • Drain any standing water, such as kiddie pools or bird fountains, where mosquitoes like to breed.