In the largest-ever study of coronavirus cases outside China, 26% of patients died. Their symptoms came in 'clusters.'

• In the largest-ever study of hospitalized coronavirus patients outside China, 26% of patients died and less than half had left the hospital alive by May 3.
• Unlike in previous studies of this scale, the researchers identified obesity as a risk factor for severe illness or death.
• Symptoms appeared in "clusters," like respiratory issues or digestive distress, and many patients had no cough or fever.

Obesity could make coronavirus patients more vulnerable to severe illness, and symptoms may appear in clusters.

In the largest study to date of coronavirus patients outside China, published Friday in the medical journal the BMJ, researchers analyzed data from 20,133 patients hospitalized across the UK.

The study identified four major risk factors that can make a person more susceptible to severe illness or death from COVID-19: age, male sex, obesity, and underlying conditions affecting the heart, lungs, kidney, or liver.

Previous studies of this scale have not highlighted obesity as a risk factor. The hospitalized patients' median age was 73, and 60% of them were male.

All in all, 26% of patients in the study died and about one-third remained in the hospital.

Less than half of the patients had left the hospital alive by May 3, when the researchers wrote the study. They were all hospitalized between February 6 and April 19.

'Clusters' of symptoms, sometimes with no cough or fever

Patients appeared with three "clusters of symptoms," the study authors wrote.

That includes musculoskeletal symptoms like muscle aches, joint pain, headache, and fatigue. Gastrointestinal symptoms, which appeared in 29% of patients upon their admission to the hospital, include abdominal pain, vomiting, and diarrhea. A less common "mucocutaneous cluster" included symptoms like skin ulcers and rash.

Though cough, fever, and shortness of breath — the respiratory cluster — remained the most common symptoms, they each only appeared in roughly 70% of patients. Some patients had no respiratory symptoms at all.

"The current case definition of cough and fever, if strictly applied, would miss 7% of our inpatients," the study authors wrote.

About 4% of the patients had only gastrointestinal symptoms, though the authors noted that "this figure could be an underestimate because these patients fall outside standard criteria for testing."

The study is ongoing and has recruited more than 43,000 patients, according to a press release. The researchers expect to release more results in the future.