A new Texas study found that the West Nile virus is deadlier than researchers and doctors once thought.

The Centers for Disease Control and Prevention has stated the West Nile virus has a fatality rate of roughly 4 percent, but a new study from the Baylor College of Medicine in Houston suggests the fatality rate could be as high as 13 percent.

The study analyzed data from all 4,162 cases of West Nile reported to the Texas Department of State Health Services between July 2002 and December 2012. Out of those cases, 289 people died of the disease within the first 90 days of infection. A remaining 268 people died after the initial onset of the illness, and it’s this number that has researchers and doctors taking notice.

The patients who died after 90 days had already recovered from the illness but were left vulnerable to other infectious diseases, according to the study. Those patients had a higher risk of dying from kidney problems and renal failure than the general population.

West Nile is a mosquito-borne virus that first came to America in 1999. It causes symptoms in about one out of every five people infected.

The people who contract West Nile fall into two categories, Josh Stevenson, the public health emergency preparedness manager for the Grayson County Health Department, explained.

“West Nile sort of falls into (two categories) either the lucky group of people who gets it and doesn’t have any signs, symptoms or maybe has some mild flu-like symptoms, or you’re the unlucky portion of people who get it and it is a very serious disease,” Stevenson said.

One person in Grayson County died of the disease in September, after being diagnosed with the neuroinvasive form of the disease, where the virus travels to the brain or spinal cord.

“Just having experienced the first death in the county from the West Nile virus, we take it very seriously,” Stevenson said. ”And this particular time of year is really the most dangerous time of year for West Nile Virus.”

Temperatures have stayed mild this year and it will take at least two hard freezes before mosquitoes will be killed off for the winter, he said.

In the meantime, evening events have been bringing more people outdoors and that means more people can be bitten.

Stevenson said people should take precautions by applying a bug spray with deet whenever they’ll be outside around dawn or dusk, the time of the day the mosquitoes carrying West Nile are most active.

Cities in Grayson County do not regularly spray for mosquitoes, which Stevenson explained was because of the cost.

Pottsboro City Manager Kevin Farley said budgetary constraints keep the city from paying for it.

In the 10 years Farley has been with the city he said it has never sprayed, but Pottsboro does treat creeks with mosquito dunks.

“Nothing inside the city limits has tested positive for West Nile,” Farley said.

The people most effected by the disease tend to be over 60 years old, as was 91-year-old Irene Crain of Denison, who died from the disease in September.

Stevenson said when he was growing up, the worst thing he could get from mosquitoes was a bump on the arm.

Now there’s West Nile and the Zika virus to contend with and he urges people to take precautions and protect themselves.

“It’s not a nuisance anymore,” he said. “Now it’s a public health risk and just like we have to put on sunscreen when we go outside, now when you go outside during mosquito season, you need to put on some deet and take precautions.”