U.S. health officials say there's been an alarming increase in the number of West Nile cases with Texas being hit hardest.

So far there have been more than 1,100 cases reported through the middle of August. That's three times as many as usually seen at this point in the year. About half the cases are in Texas. Most West Nile infections are reported in August and September.

The Centers for Disease Control and Prevention reported the new numbers Wednesday. They say the mild winter, early spring and very hot summer have fostered breeding of the mosquitoes.

But, according to the Star-Telegram, the CDC numbers may be delayed compared to the cases actually detected in North Texas. Analysis by the paper claimed the numbers from the federal health officials could be underreporting fatalities by 70 percent.

NBC 5's own record-keeping of the total number of West Nile human cases reported by local health officials brings the total number to 662 as of Aug. 21; CDC numbers only reference 537 infections in the entire state.

Four more West Nile virus deaths have been reported in Texas, bringing the state's 2012 total to at least 26.

Houston health officials report their second and third West Nile deaths of the year.

Two more were reported in the Dallas area, which has been the focus of this year's U.S. outbreak. One death in Dallas County and one in Collin County brings the Dallas-Fort Worth area's death toll to 18, by far the most in the country.

More than 270 human cases have been confirmed in Dallas County alone, which has begun aerial spraying for mosquitoes.

Harris County officials have scheduled aerial spraying for Wednesday in northwestern Harris County.

Mosquitoes spread the virus from birds to people.

West Nile virus was first reported in the United States in 1999.

Complete coverage of the West Nile virus outbreak in North Texas can be found in our Special Section.

NBC 5's Greg Janda and Associated Press writer Mike Stobbe contributed to this report.