A CDC study published Monday focusing on the public health responses to the coronavirus outbreaks on cruise ships discovered the virus lived on surfaces 17 days—much longer than previously believed.

The study looked at the U.S. and Japanese government responses to contain the outbreaks on the Diamond Princess ship in Japan and the Grand Princess ship in California.

“Cruise ships are often settings for outbreaks of infectious diseases because of their closed environment, contact between travelers from many countries, and crew transfers between ships,” the CDC states, noting there was a high proportion of asymptomatic travelers, which could help explain why the outbreaks were so bad.

“SARS-CoV-2 RNA was identified on a variety of surfaces in cabins of both symptomatic and asymptomatic infected passengers up to 17 days after cabins were vacated on the Diamond Princess but before disinfection procedures had been conducted,” according to the study.

Whether the virus was transmitted by infected surfaces was not able to be determined by the data, however, and the study called for further research into “fomite transmission.”

Researchers previously found that the virus lived up to one day on cardboard, three days on plastic and stainless steel, and four hours on copper.