About 900 migrants held in Immigration and Customs Enforcement (ICE) custody have been exposed to mumps since last September, according to the first U.S. government report on outbreaks in the nation's overloaded immigration system.

The U.S. Centers for Disease Control and Prevention (CDC) reported Thursday a total of 898 confirmed and probable mumps cases in adult migrants in 57 facilities housing ICE detainees across 19 states since September 2018. The virus also sickened 38 staffers in that time span.

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More than 80 percent of the patients who fell ill with the mumps at the detention centers were first exposed to the virus while in the custody of ICE or another U.S. agency, according to the CDC report.

ICE spokesman Bryan Cox told The Associated Press medical professionals at detention facilities screen all new detainees within 24 hours of their arrival to ensure that highly contagious diseases are not spread. Cox said some detainees come from countries where communicable diseases are less controlled than in the U.S. and carry with them the risk of spreading infection.

Mumps is a contagious virus that causes swollen glands, puffy cheeks, fever, headaches and, in severe cases, hearing loss and meningitis. Critics claim U.S. immigrations officials are not doing enough to quarantine migrants and prevent the spread of infectious disease in overcrowded detention centers.

“This has all the makings of a public health crisis,” Nashville immigration attorney R. Andrew Free, who has been tracking facilities with mumps outbreaks from reports of advocates and lawyers representing detainees, told The Associated Press. “ICE has demonstrated itself incapable of ensuring the health and safety of people inside these facilities.”

A large portion of the cases recorded by the CDC were reported at detention facilities in Texas. The Texas Department of State Health Services raised the alarm in December, followed by six other state health departments in early January, prompting what the CDC report calls “a coordinated national outbreak response.” ICE has given more than 25,000 doses of measles-mumps-rubella (MMR) vaccine in the affected facilities, according to The Associated Press.

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In the U.S., vaccines have drastically reduced the number of mumps cases. Only a few hundred cases are reported most years, with periodic outbreaks involving colleges or other places where people are in close contact.

The CDC report dealt only with mumps, not other health problems in detention facilities. At least two migrant children have died of complications of the flu after being detained by U.S. Border Patrol. The agency recommended detention facilities follow guidance from state and local health departments when responding to mumps.

The Associated Press contributed to this report.