Officials are reporting a spike in flu cases in Texas with more than a dozen deaths in the Houston area, most of which were caused by the H1N1 strain that's also known as the swine flu.

KHOU in Houston reports that 13 people have died in Houston so far, including a teenager.

Kathy Barton, spokeswoman for the city's health department, said the teenager was infected with the H1N1 strain of the virus.

About 95 percent of the influenza A cases in Texas are H1N1.

Physician Dr. Richard Honaker, of Family Medicine Associates of Texas, has been ordering a lot of rapid flu tests. Dr. Honaker says the past two days have been the busiest so far this season. He usually sees one case a day, right now, that number is four or five

“There are different strains H1N1 is the most common strain so that is what we are really seeing... Most of them tend to be h1n1,” said Dr. Honaker.

In Dallas County, influenza cases have risen from one in the first week of October to 167 in the first week of December. December flu numbers will not be released until January.

“At Christmas time people gather together so more germs spread. Also people are stressed out so their immune systems are low. So you put those two things together and boom you have a mini epidemic,” said Dr. Honaker.

Dr. Honaker says the flu shot is effective about 90 perfcent of the time. Many people are treated with Tamiflu, and he added that is most effective if started within the first 48 hours.

The Centers for Disease Control and Prevention said Texas is one of six states with "high" activity of influenza-like illnesses. Texas, Mississippi, Alabama and Missouri are at the highest level of activity, while Louisiana and Oklahoma, while not quite as high as the previous four, are also at a high level of activity, according to the CDC. See a map here

State health officials said influenza has become widespread across Texas, which is not unusual for this time of year.

Officials with the CDC advise Texans who have not yet received a flu shot that there is still time to get one for this flu season.

NBC 5's Julie Fine contributed to this report.