New Jersey health officials on October 31 confirmed four adenovirus cases at Voorhees (N.J.) Pediatric Facility.
State health experts believe the children were exposed between September 26 and October 29, but symptoms can appear as many as 14 days after exposure.
The department also said Thursday the illness was last detected on Tuesday, Oct. 30. Symptoms - including the common cold, sore throat, bronchitis, diarrhea, pink eye and fever - usually appear two to 14 days after a child is exposed to the virus.
Meanwhile, the state says there are four confirmed adenovirus cases among pediatric patients at Voorhees Pediatric Facility, near Philadelphia.
Like the others, the child, who was staying at the Wanaque Center for Nursing and Rehabilitation in Haskell, was infected with adenovirus, the state's health department confirmed in a statement Wednesday night. One death was a young adult.
The affected children had severely compromised immune systems, including respiratory problems, before the outbreak began, the DOH said. But it can be serious in people with weakened immune systems, like those at the centre.
"We are working closely with the facility to conduct respiratory illness surveillance and ensure all infection control protocols are continuously followed", New Jersey Health Commissioner Dr. Shereef Elnahal said.
Health experts say that the amount of time it takes to respond to a potential outbreak and notify families is variable and may depend on how long they need to investigate an outbreak, culture a virus and confirm its identity.
"The vast majority are under age 18".
The strain found in the Wanaque rehab center outbreak is called type 7 and is among the more potent types.
Elnahal had earlier said all the cases of the outbreak occurred in a respiratory, or ventilator, unit.
"The strain of adenovirus seen in this outbreak is associated with communal living arrangements and known to cause severe illness", the state health department said.