The Texas Department of State Health Services is urging people to make sure they are immunized against whooping cough after six deaths and more than 1,000 cases so far this year.
The health department said Thursday the six deaths are the most for a single year since 2005.
The deaths have included five infants younger than 2 months old, the age when the first vaccination is recommended. The health department said it demonstrates how important it is for parents and others around newborns to get the recommended doses.
"There are some states that are seeing 10 time as many cases this year as they saw last year. We're certainly seeing more cases at Children's," said Dr. Jeffrey Khan at Children's Medical Center of Dallas. "Last week, we had a very young child who died of pertussis, which is a tragic reminder that this is a lethal disease that should be taken very seriously."
The sixth death was an unvaccinated older child with underlying medical conditions.
A 4-year-old Burleson boy, Gunner Mays, was diagnosed with the illness after he started having violent coughing fits.
"The cough would just not let up," said his mother, Bonnie Mays. "It was a scary cough. He would start coughing and be like, 'I can't breath.'"
After taking him to the hospital twice in two days, doctors diagnosed him with pertussis.
"I was pretty much floored," his mother said.
There were 961 total Texas cases of pertussis last year, down from a peak of 3,358 in 2009.
Whooping cough, or pertussis, is a contagious bacterial illness that can lead to severe coughing.
NBC 5's Catherine Ross and Scott Gordon contributed to this report.