The new coronavirus lingers for as long as three weeks in the bodies of patients with severe disease, Chinese researchers reported Tuesday.

The virus can be found deep in the lungs and in the stool of patients, and the sicker they are, the longer it stays, the team at a hospital in China’s Zhejiang province reported. But the virus was found in the urine of patients less than half the time, and rarely in the blood at first.

Their report provides another piece of evidence about the pattern of disease in Covid-19 patients. It published in the BMJ. Unlike many recently released studies about the coronavirus, this one has gone through peer review, which means other experts have reviewed the findings.

The team tested 96 patients treated in their hospital for Covid-19 between January and March. They tested samples from the nose and throat, from deeper in the respiratory system, in the blood, stool and urine. They wanted to see how long people had virus in their systems and whether it was likely to spread in various ways. The findings support other studies showing that the virus could spread in stool from infected people.

In general, the sicker people were, the longer the virus could be detected. That could be important for doctors to know, so they can predict which patients will fare better, and, perhaps, how long they may remain infectious to others.

“The median duration of virus in respiratory samples was 18 days,” they wrote.

More on this: An earlier Chinese study showed that people without symptoms had just as much virus in their noses as people who had Covid-19 symptoms – something that indicated people who are not sick could be just as likely to spread virus as people who are.

The team in Zhejiang found that sicker people had more virus deeper in their respiratory tracts, however.

They also found differences between men and women with Covid-19. “In this study, we found that the duration of virus was significantly longer in men than in women,” they wrote.

“Our results shed light on the causes of disease severity in men in terms of the duration of the virus. In addition to differences in immune status between men and women, it has also been reported to be related to differences in hormone levels,” the team wrote.