(CNN) — An immigrant detained at a federal prison in California has been diagnosed with chickenpox, raising concerns among the prison staff.

The detainee is among 1,000 immigrants in federal custody who were recently moved to the Victorville Federal Correctional Complex, about 90 miles northeast of Los Angeles, according to US Immigration and Customs Enforcement.

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But John Kostelnik, president of the union representing the prison’s workers, said the California facility is understaffed and the arrival of the ICE detainees two weeks ago has made things worse.

“It’s causing a lot of chaos, a lot of confusion and quite frankly that confusion can lead to someone being killed or something else going wrong,” Kostelnik said.

There’s not enough doctors to accommodate all the detainees. Other detainees have been diagnosed with scabies and some have tested positive for tuberculosis, Kostelnik said.

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Federal authorities said they have been working with the US Marshals Service, the Bureau of Prisons and private detention facility operators to find additional bed space after a recent surge in illegal border crossings.

“The use of BOP facilities is intended to be a temporary measure until ICE can obtain additional long-term contracts for new detention facilities or until the surge in illegal border crossings subsides,” ICE said in a statement.

The agency is closely monitoring the situation and “is confident in the care and oversight provided by the Bureau of Prisons and believe these are extremely safe and secure facilities for ICE detainees.”

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CNN has reached out to the Bureau of Prisons but a request for comment was not immediately returned.

In New York City, some of the migrant children recently separated from their parents were also diagnosed with chickenpox and other contagious diseases, Mayor Bill de Blasio had said.

Chickenpox is a highly contagious disease that is caused by the varicella zoster virus.

The virus causes an itchy blister-like rash that can be dangerous, particularly for people who get it late in life.

It is an airborne virus, so that means it can spread by breathing in the virus particles that come from the chickenpox blisters.

Chickenpox has become more rare since so many children have been vaccinated for it. The vaccine first became available in 1995.

For adults who get chickenpox, there can be more serious complications like pneumonia. Other symptoms include a loss of appetite, headache, tiredness and fever.

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