From the Austin command center, Sidwa manages the state effort to track the West Nile outbreak. He said his team got an early warning months ago from routine testing of donated blood.

West Nile cases in U.S.

“This year we got advance notice that there was activity by virtue of that testing and people who were donating blood testing positive for West Nile. That does not mean they are sick. Some of them may be, but they have the virus in their system,” he said.

Most infected people unaware of it

Sidwa said most infected people are unaware of it. Symptoms can include fever, headache and feeling tired. For the small percentage whose brains are affected by the virus, it can be debilitating and even deadly.

“The way it manifests is everything from 80 percent of the people with no symptoms, to 20 percent with a lesser disease, and roughly one percent - or one in 150 - will develop the severe neurological form of the disease,” said Sidwa.

As the hot weather subsides in the weeks ahead, Sidwa said he expects the number of reported West Nile cases to taper off. And he said what has been learned this year will help in dealing with future outbreaks.