A seventh child has died as a result of a adenovirus outbreak at a rehabilitation center in New Jersey, health officials said Wednesday.

The New Jersey Department of Health announced Tuesday that six children had died and 12 others were sickened at the Wanaque Nursing Home & Rehabilitation Center in Haskell. On Wednesday, the department said a seventh child involved in the outbreak had died on Tuesday night, while 11 remain ill.

It's unclear how long the center has been dealing with the outbreak. It's also unclear how old the children who died or those still sickened are, and what conditions they were originally being treated for.

The Centers for Disease Control and Prevention and the New Jersey Department of Health are investigating the outbreak, and the facility has been instructed not to admit any new patients.

Over the weekend, the health department found "handwashing deficiencies" and "infection control issues" at the rehabilitation center, which houses senior, rehabilitation and pediatric patients.

In 2016 and 2017, the center was cited for hand washing deficiencies, improper storage of syringes, failure to disinfect surfaces and syringes properly and the unsanitary storage of oxygen tank tubing, all of which prevent the spread of infection. The center was also cited in August for failing to prevent the spread of infection.

"As we grieve, we are urgently seeking clarity from the facility administration regarding the processes being put in place to safeguard patients," said a statement from1199SEIU United Healthcare Workers East, which represents 136 workers at the center.

"Since new for-profit ownership took over at Wanaque Center in 2014, workers have expressed serious concerns over worsening staffing levels, lack of adequate supplies, and severe cutbacks to job standards," said the statement from Ron McCalla, the union's vice president.

New Jersey Gov. Phil Murphy said Tuesday that "the Department of Health has recommended vital measures to enhance protections against the further spread of infection and will continue its active on-site surveillance."

In a statement released Tuesday, the Wanaque Rehabilitation Center said that it had promptly notified "all appropriate government agencies," including the Centers for Disease Control, when staff discovered the adenovirus cases.

"The Wanaque Center continues to fully cooperate with these agencies and has sought out their medical guidance with respect to the virus," the statement said.

Adenoviruses usually cause mild infections of the respiratory tracts, eyes, intestines, urinary tracts, and nervous systems of young children.

The particular strain that's affecting Wanaque "is affecting medically fragile children with severely compromised immune systems," the health department said. "The strain has been particularly associated with disease in communal living arrangements and can be more severe."