A mumps outbreak in Johnson County has grown to 57 cases, a 20-case increase from last Thursday, according to health authorities.
Along with the Johnson County outbreak, unrelated cases in Collin, Dallas, Denton and Tarrant counties have been identified, according to a health department advisory sent out Tuesday afternoon.
Collin County has two confirmed cases. Denton County has three reported cases.
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In Dallas County, eight adults have been diagnosed with mumps. Six of the cases were contracted at the same Halloween party, and two others are unrelated. One person traveled back from Minnesota and another from Arkansas, according to Dr. Christopher Perkins, medical director of the Dallas County Department of Health and Human Services.
"What is unique about this is that when it comes to mumps, the vast majority are vaccinated," Perkins said.
The vaccine has an 88-percent success rate, he added, which means 12 percent of people remain at risk.
Children are given the vaccine in two doses – once between 12-15 months and again between ages 4 and 6.
"So what we're seeing is that as these individuals progress and become young adults, we unfortunately have a sporadic outbreak of mumps," Perkins said. "It might be that they might consider another dose at some point."
Perkins said Dallas County typically sees two to three cases per year.
"So, yes, this is concerning," he said.
Health officials also warned they expect to see even more cases over the next few weeks because of holiday travel.
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.
Nationwide, 4,258 mumps cases have been reported as of Dec. 3 this year, according to the Centers for Disease Control and Prevention.
Mumps can look like the flu and spreads through infected saliva.
"I'm looking for high fevers, sore throat or swollen throat," said nurse practitioner Veronica Teran, with Children's Health Pediatric Group. "Muscle aches, tiredness, headaches, are they not eating as well?"
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.
"Everybody gets the first vaccine at the age of one, and then usually when it's time to start school it's time to get the second one," Dr. Elvin Adams, Johnson County Health Authority.
"The preschoolers have, by and large, only had one, and so to give them extra protection we're recommending they get that second dose early," Adams said.
"Hand washing is also very important, especially in children, because they do share a lot of germs, and they put their hands in their mouths and then they play together," Teran said.