A new study of people in the New York City area who have been hospitalized with COVID-19 reveals that most of them have more than one underlying illness, some of which seem to increase their risk for bad outcomes.

In the new study, published in the Journal of the American Medical Association (JAMA), researchers wanted to learn more about people who are hospitalized after contracting the novel coronavirus. They looked at electronic health records data from 5,700 people with COVID-19 who had been admitted to hospitals within the Northwell Health system—which currently has the largest number of COVID-19 cases in the country—in the New York City area in March and early April. The median age of patients was 63 years old, and 94% of them had at least one comorbidity, meaning that they had at least one other disease in addition to COVID-19.

The most common were hypertension (affecting about 53% of all COVID-19 patients), obesity (affecting about 42% of patients with BMI data) and diabetes (affecting about 32% of all patients).

Researchers then looked at outcome data from the 2,634 patients who eventually left the hospital, either because they had died or had been discharged. About 14% had been treated in the intensive care unit (ICU), 12% had been on ventilators, 3% had kidney replacement therapy and 21% died. The outcomes for people placed on ventilators were grim; 88% of them died. Of the patients who died, people with diabetes were more likely to have been placed on ventilators.

“Having serious comorbidities increases your risk,” says Karina Davidson, one of the study’s authors and senior vice president for the Feinstein Institutes for Medical Research, which is part of the Northwell Health system. “This is a very serious disease with a very poor outcome for those who have severe infections from it. We want patients with serious chronic disease to take a special precaution and to seek medical attention early, should they start showing signs and symptoms of being infected. That includes knowing that they’ve been exposed to someone who has this virus.”

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Write to Mandy Oaklander at mandy.oaklander@time.com.