COPENHAGEN, Denmark — More than 40 percent of the people who died in the outbreak of Middle East Respiratory Syndrome in Italy in 2015-2016 had no known medical or environmental risk factors, a new study shows.

In comparison, previous research on the disease detected more than 50 percent of the cases were caused by people with no clear risk factors, even though the majority of the risk factors for coronavirus infections were the same as for the typical human infection, said the paper, published on Monday in the journal BMJ Case Reports.

Nujaid Sadiq of Queen Mary University of London said in a telephone interview that people with no health risk factors were more prone to spread the infection, either accidentally through infected items or through contact with those who did have such risk factors.

If people carrying the virus entered crowded places they could easily spread it around and make people with no risk factors more susceptible to infection, he said.

It is not yet clear how the C.difficile bacterium which causes C.difficile infections, which sickens 700,000 people a year in the United States alone, is carrying Coronavirus O157:H7, also called MERS-CoV.

But cases were detected in hospitals with high rates of the coronavirus in Italy, Kuwait, Oman, South Korea, Saudi Arabia, and the United Arab Emirates.