Dr. Jason Bowling, an infectious disease physician with UT Medicine, said flu cases are typically on the rise at height of the flu season, which runs from October to April.
He said the H1N1 strain is the most common, but flu vaccines are plentiful.
Bowling said University Hospital has reported increases in flu cases during the past three weeks.
"Nationally there's an increase as well and Texas is one of 20 states listed as having high activity levels of flu cases right now," Bowling said.
He said there have been some deaths, as there are every flu season.
But a spokeswoman for the Metropolitan Health District reports so far there have been no pediatric deaths in the San Antonio area.
Bowling said H1N1 can even seriously affect the young and healthy.
Asked why there are more H1N1 cases if both vaccines currently available protect against it, Bowling said some may not have been the flu.
Bowling said, "There also are many respiratory illnesses out there."
He said cold weather does not cause the flu, but it does enable it to spread because more people are staying indoors.
Bowling said he advises those who think they have the flu to stay home. And he said there is still plenty of time to get your flu shot.