The number of mumps cases in Johnson County has risen to 48, mostly in school-age children in Keene and Cleburne, the county’s health authority said Tuesday.
Fifteen additional patients are suspected of having the highly contagious virus, which often leads to facial swelling and can lead to brain infection. The state as a whole hasn’t had more than 20 cases of the virus a year since 2011.
In Johnson County, “I think we’ve peaked,” said Dr. Elvin Adams, the county health authority. He doesn’t believe the virus will spread to many more people.
Still, it’s “highly probable” more cases could be identified in the next month since the virus has an incubation period of 16-18 days, Adams said. People who get the virus can have it for up to a week before showing symptoms.
“This is why it’s hard to stop an outbreak in a school — anyone who has the virus is giving it to everyone else for about a week,” Adams said. “We don’t consider the outbreak to be completed until about 50 days after the last patient is cleared.”
Nearly two-thirds of the infected patients in Johnson County had received the mumps vaccination, which is about 88 percent effective, Adams said.
Of the 48 people with mumps, 10 have been adults.
Adams said the virus is believed to have come from an outbreak in Arkansas, where several students from Keene had visited family about a month ago. Five people, including some of the students, returned home with the virus.
Two weeks ago, the Cleburne and Keene school districts began taking precautions to prevent an outbreak, identifying students who might have come in contact with the virus.
Students who did not have the mumps vaccine were required either to get immunized or to stay home for 26 days.
Other North Texas cities have seen recent cases of mumps, CBS 11 reported.
Eight adults in Dallas caught the virus, likely at a Halloween party in October, according to the Dallas County Department of Health and Human Services. Two other cases this month were linked to out-of-state travel, according to CBS 11.
There is no treatment for mumps. Patients are often cleared of the virus in about five days, but long-term complications can include brain infection, swelling of salivary glands and pancreas — leading to pancreatitis — and swelling of the testicles and ovaries.
Infected males could become sterile, though long-term-complication rates are low, especially for patients who have been vaccinated, Adams said.
Mumps cases have declined drastically since the 1960s, when widespread vaccinations began. Before that, about 180,000 cases of mumps a year were reported in the United States, according to Centers for Disease Control and Prevention data.
Since the 1960s, the numbers have fallen by about 99 percent, now ranging from 1,000 to 2,000 cases a year.
Still, outbreaks have happened.
“The vaccine can’t ever be perfect,” said Dr. Suzanne Whitworth, medical director of infectious diseases at Cook Children’s Medical Center in Fort Worth. “We know these viruses circulate, and for whatever reason, it will just take off. Mumps is really contagious.”
This year, nearly 2,879 cases nationwide had been diagnosed as of Nov. 5, already the most since 2006, when more than 6,000 people were diagnosed.
In Texas, about 38 cases a year were diagnosed from 2005 to 2015, peaking at 121 in 2010, according to Department of State Health Services data.