The number of mumps cases in Johnson County has jumped to 37, and a dozen more are suspected. Nearly half are in the Keene Independent School District.
District officials say they are doing all they can to protect students, and that includes a large vaccination drive this week.
Superintendent Ricky Stephens says Keene Elementary School is practically ground zero, which is what parents, administrators and county health officials feared most when the outbreak started.
"Some of them are relatives, but the most common thing is that they are students in the same school. This is what is a concern to us," Dr. Elvin Adams, with Johnson County Health Authority.
County health officials believe a family trip to Arkansas is how the virus got to North Texas. It's part of a larger outbreak that has hit schools in almost every state this year.
"Mumps is highly contagious, so yes this is kind of a new wrinkle," said Lisa Magers, with the Cleburne Independent School District.
With a few weeks left in 2016 the Centers for Disease Control and Prevention says there are 3,832 cases and counting. That is nearly triple the number last year.
Local
The latest news from around North Texas.
Mumps can look like the flu and spreads through infected saliva. With water fountains off-limits, students are being given bottled water. And additional wipe-downs continue at all Keene ISD schools, where those infected with the disease have already been pulled from class.
There's no word from the CDC as to why this outbreak has been so severe.
People who lack the proper immunizations are at the highest risk of getting the mumps. On Tuesday, Keene ISD vaccinated 74 people, including about 10 children.
