Federal prisons, whose inmates may be a high-risk population for a coronavirus outbreak, do not have kits to test for the disease available.

“Once we receive concurrence from local health authorities that a test should be conducted, samples would be collected and sent back to the designated lab for testing,” Federal Bureau of Prisons spokeswoman Nancy Ayers said in an email this week.

Concerns are growing in Congress over how prepared federal prisons are to face any potential coronavirus outbreaks. Experts have long recognized that prison inmates, who live in close proximity to each other and often have underlying health conditions, can be highly susceptible to infectious diseases.

“The risk of community spread poses a critical and unique threat to vulnerable populations, including those in our prisons and jails,” California Democratic Sen. Kamala Harris wrote in a letter to the Bureau of Prisons on Thursday.

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There are “no known cases of COVID-19” in a federal prison right now, Ayers said. But it has shared guidance on the virus with its health care workers “out of an abundance of caution.” The bureau declined to share with CQ Roll Call the guidance that it has sent its health care workers.

The union that represents federal prison guards did not respond to requests for comment.

This week marked a dramatic turn as more cases of the disease were acquired by person-to-person transmission in the U.S. rather than overseas. That’s raised alarms among public health experts, who worry that the virus, which spreads easily and is believed to have a fatality rate significantly higher than the seasonal flu, may become widespread.

Current evidence shows that the virus is particularly dangerous for the elderly and those with preexisting health conditions.

There were 260 confirmed cases of COVID-19 in the United States as of Friday afternoon, including 14 deaths, according to Johns Hopkins University. But those numbers are likely to rise sharply as more Americans are tested for the virus. A tally by The Atlantic found that fewer than 2,000 people in the U.S. had been tested as of Friday morning.

A coronavirus vaccine is in the works but could be a year or more away. There are no approved treatments for the virus.

Public health officials have urged Americans to wash their hands often, avoid crowds and stay home from work if they are sick. Those tactics could prove more difficult in the often crowded conditions of federal prisons, where items like alcohol-based hand sanitizers are banned and inmates live in close quarters.