"As a result, facility staff have diligently implemented all available infection control and prevention measures in order to protect the health and safety of the Wanaque Center's residents", center officials said.
A Department team is at the facility today and an inspection team was also there Sunday.
Adenoviruses usually just cause mild illnesses.
Adenoviruses are the cause of everyday infections like the common cold, bronchitis, pink eye and respiratory tract infections, but the highly contagious viruses can be much more risky to people with already compromised immune systems.
The facility was instructed not to admit new patients until the outbreak ends, and the Health Department said the number of new cases appears to be decreasing.
The 18 patients range in age from a toddler through young adulthood and most are under 18 years old, health department spokeswoman Nicole Kirgan said in an email. Health officials are working with the center on infection control issues.More news: Turkish President Erdogan: Jamal Khashoggi's Death Was A 'Planned Operation'
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"This strain has been particularly associated with disease in communal living facilities", the department said in a statement.
The facility houses an adult nursing home, a rehabilitation center and a pediatrics unit.
"It can cause pretty much like a common cold type of illness in the majority of the population", Javaid said, adding that if someone's immune system is compromised a minor cold can turn into something much worse.
New Jersey Governor Phil Murphy said in a statement Tuesday that state and local health officials are working to contain the outbreak.
Those who have weakened immune systems are at an increased risk of developing a severe illness or neurological diseases from an adenovirus infection.
A rep for the center didn't immediately return a message.