FORT WORTH (CBSDFW.COM) – The flu is spreading rapidly in North Texas. Late last week, there were seven hundred cases.  As of Monday, the number has grown to more than 18-hundred confirmed cases.

As kids across North Texas head back to class, there is fear the number of flu cases will continue to spike.

Dr. Jill Strachan-Batson with Parkland Hospital says people with the flu are contagious for a longer period of time than they realize.

“The flu is something that is spread by close contact by respiratory droplets, so with kids, congregating in areas and hugging and shaking hands and talking to one another, there is the opportunity for them to spread this germ,” she said.

Hospitals, county health authorities and others are detailing rising flu cases, and also emphasizing the severity of illness the flu is bringing. Dallas County health authorities report more than one hundred people admitted to hospitals, as a result of the physical impact this virus is having on individuals.  Over the past two weeks, 60 people were treated in intensive care units, all with the H1N1 virus.

At Medical City Dallas, the number of flu patients seeking treatment have tripled in recent weeks.  “The number of positive flu tests we’ve had in the last couple of weeks are up eight times what they were in early December, so without a doubt we’re seeing a lot of flu, said Dr. Matt Bush.  Officials at Medical City are so concerned about the spread of the flu, they are asking parents not to bring their kids to visit hospital patients.  JPS Health Network has made the same request.

At least 20 flu deaths have been reported across North Texas.  Denton County health department reported their first two flu-associated deaths on Monday, one of them a young girl from Carrollton, who attended a Lewisville charter school.  Dallas County officials confirm 17 flu related deaths and they say the virus is hitting people of all ages hard.

“Young adults, healthy adults are being impacted tremendously with the illness. The illness has really hit them hard.  We’re talking healthy adults,” said Dallas County Health and Human Services Director Zachary Thompson.

Dr. Strachan-Batson stresses getting a flu shot is the best defense, but warns it will take two weeks to work.

Denton County is offering free flu shots Tuesday at clinics in Denton and Lewisville.  Dallas County Health and Human Services is offering free flu shots to residents who qualify.  Tarrant County’s Health Department has the vaccine available at $20 a shot.  Click here to type in your zip code and find a flu shot near you.