The source of exposure in a deadly Legionnaires’ outbreak on the Upper East Side has been “eliminated,” the city’s health commissioner, Dr. Alister Martin, said Friday.

The announcement came one day after city officials reported a seventh death linked to the outbreak.

“We can confidently close this phase of our response, because the incubation period — meaning the stretch of time during which new illnesses can arise — has passed,” Martin said on a press call. “Legionnaires’ disease has a 14-day incubation period. Within that time frame, we have seen no new cases with onset of symptoms in the last two weeks.”

Residents living in ZIP codes 10128, 10028 and 10075 on the Upper East Side no longer face an “elevated risk” of the disease, he added.

As of Thursday, the city’s Health Department said 92 people had been sickened by the outbreak, 79 of whom were hospitalized, with five still in the hospital.
Health officials reported the first of the seven deaths linked to the cluster two weeks ago.

“I offer my deepest condolences to the families and friends of those we have lost,” Martin said.  

More than 90% of those who fell sick developed symptoms before July 7, five days after the Health Department began investigating the outbreak, the agency said.

The department said it has tested 183 cooling towers at 160 buildings in the affected ZIP codes. Seventy-seven cooling towers at 75 buildings initially tested positive for Legionella bacteria, while 59 cooling towers at 58 buildings tested culture positive, confirming the presence of live bacteria, officials said.

All culture-positive cooling towers have been cleaned and disinfected, according to the department. In total, 124 cooling towers have tested culture negative.

"Our data shows that the source of bacteria exposure causing this cluster has been cut off,” Martin said, while noting that “further testing is underway to pinpoint the source, and that testing is called whole genome sequencing analysis.”

“What we do there is, we collect and sequence the genome DNA from people who got sick and from the culture positive cooling towers,” he said. “Now, if there's a match between the cooling towers and the patients, that tells us which cooling tower towers made people sick in this cluster.”

The results of that testing are expected in late August, he added.

Legionnaires' disease is a form of pneumonia caused by Legionella bacteria, which grow in warm water and can spread in building cooling systems, hot tubs and showerheads. In many cases, people contract the disease by inhaling tiny droplets of contaminated water; Legionnaire's doesn't spread person-to-person.

The illness is treatable, but it is fatal in about 10% of cases, according to the U.S. Centers for Disease Control and Prevention. 

Last year, more than 100 people were sickened during a Legionnaires’ outbreak in Harlem, seven of whom died.