CDC reports more than 900 mumps cases in immigrant detention centers "These centers are a perfect storm for mumps to spread," a doctor says.

Immigration detention centers across the U.S. are fighting the first outbreak of mumps in their facilities, according to a new report by the Centers for Disease Control and Prevention.

The report, released Thursday, says that there have been 931 cases of mumps in a total of 57 Customs and Border Protection (CBP) and Immigration and Customs Enforcement (ICE) detention facilities in 19 states in the last year. The cases have affected both detainees and staff.

"These detention centers are a perfect storm for mumps to spread. Individuals have to be within 3-6 feet of each other to spread this virus. Sneezing, coughing on someone, or sharing a drink can spread the virus.” Dr. Todd Ellerin, Director of Infectious Diseases and Vice Chair of Medicine at Southshore Health in Massachusetts, told ABC News.

In June the Department of Homeland Security's inspector general found egregious conditions at CBP facilities, with migrants packed into standing room-only surroundings, often without the ability to bathe for days.

Although the CDC says immunization is the most effective way of preventing mumps, CBP officials say that they do not routinely offer the mumps vaccine to detainees.

“In general, due to the short-term nature of CBP holding and the complexities of operating vaccination programs, neither CBP nor its medical contractors administer vaccinations to those in our custody,” a Customs and Border Protection spokeswoman said in a statement.

In ICE facilities, “flu and other common vaccinations are offered by request only and are not routinely mandated unless deemed medically necessary, in that doing so would prevent a wider outbreak,” an Immigration and Customs Enforcement official said in a statement.

Many doctors, like Ellerin, support vaccination.

“From a public health perspective, I feel strongly that the benefits of vaccinating detainees against the flu and mumps outweighs the risks," Ellerin told ABC News. "This is about protecting the individual, which in turn protects the staff and the population at large.”

“In 2017 the CDC started recommending a third dose of MMR vaccine to those individuals who are in an outbreak setting. It is important that the staff receive maximal vaccination to avoid spreading the virus to their families, children, and communities,” he added.

Many see this mumps outbreak as foreshadowing a possible flu outbreak later this flu season.

“Other viruses spread through respiratory droplets, include influenza,” Ellerin said.

The mumps is a viral infection that can cause fever, headache, muscle aches, and swollen cheeks, according to the Mayo Clinic. The swollen cheeks are due to an infection of the salivary glands, which can cause pain with chewing or swallowing.

Mumps is spread by "respiratory contact from one person to another,” said Dr. Nanda Ramchandar, a pediatric Infectious Disease doctor at University of California, San Diego. "Eighty to ninety percent of non-immunized household contacts will contract the virus. That is a really high rate of transmission.”

According to the CDC, mumps has a long incubation time, so it can present up to 25 days after infection. Complications are rare, but are more likely to occur in unvaccinated people.

There are additional complications for men. "Though many affected men will recover without complications, a feared complication is orchitis,” Ramchandar said. Orchitis is a swelling of the testicles, and can cause diminished testicular function.

Less than 1% of people infected with mumps will suffer from complications involving the brain.

It is difficult to pinpoint the first case of mumps in U.S. detention centers. But while vaccination rates lag in many European countries, the CDC says there are high vaccination rates in Central American countries. According to the CDC report, “Vaccination coverage in El Salvador varies from 90% to 93%, depending on the vaccine, while vaccination coverage ranges from 93% to 98% and 88% to 93% in Guatemala and Honduras, respectively. El Salvador, Guatemala, and Honduras administer vaccines in accordance with the World Health Organization’s (WHO) Expanded Program on Immunization.”

Beyond immunization, other standard prevention techniques recommended by the CDC include hand washing and decreasing contact with people who are sick.

There have been several recent domestic mumps outbreaks, most notably almost 3,000 cases in a tight-knit Arkansas community in 2016-2017.

"Every year, hundreds of thousands of people are hospitalized and thousands or tens of thousands of people die from flu-related causes every year," reports the CDC, which says that an annual seasonal flu vaccine is the best way to help protect against flu.

Sejal Parekh, MD, is a pediatrician in San Diego who is currently writing for ABC News' Medical Unit.