Nearly all coronavirus patients who needed ventilators in New York's largest health system to help them breathe died, a study found.

Overall, about 20% of COVID-19 patients treated at Northwell Health died, and 88% of those placed on ventilators died, according to the study. A ventilator is a device that forces air into the lungs of patients who cannot breathe on their own because of severe pneumonia or acute respiratory distress syndrome.

Other, smaller reports have indicated that patients who need ventilation are unlikely to survive.

Just 12% of the patients in the study needed ventilators, Dr. Safiya Richardson at the Feinstein Institutes for Medical Research, Northwell Health, and colleagues found.

But this study, published in the Journal of the American Medical Association, shows how dire the outlook is for patients with severe COVID-19 disease.

The team looked at the electronic health records of 5,700 patients with coronavirus disease hospitalized at Northwell Health. Final outcomes were known for 2,634 of them.

The records support what doctors have been saying about the coronavirus: most people who become severely ill have some sort of so-called underlying condition. More than half, or 57%, had high blood pressure, 41% were obese and 34% had diabetes.

"Of the patients who died, those with diabetes were more likely to have received invasive mechanical ventilation or care in the ICU compared with those who did not have diabetes," the researchers wrote.

They also confirmed that men were more likely to die than women, and no one under the age of 18 died.

The symptoms of infection were far from clear-cut. About a third of all patients showed up with fevers, 17% were breathing too fast and just under 30% needed extra oxygen. On average, patients were sent home after four days.

But 14% were treated in intensive care, 3% needed intensive dialysis and 21% died.

Since final data was only available on about half of the patients, it's possible that more of those on ventilators survived, the researchers said -- something that would drive down the 88% fatality rate for that group.

"This study reported mortality rates only for patients with definite outcomes (discharge or death), and a longer-term study may find different mortality rates as different segments of the population are infected," the Northwell Health team wrote.

First Published: April 23, 2020, 8:02 a.m.