Around half of the healthy adults are exposed to cytomegalovirus (CMV) and their immune systems control its spread without any signs of infection, according to the research.
However in patients with damaged immune systems, the virus can reactivate and cause health problems.
But according to the US study of 120 patients admitted to ICU without any immune problems, one in three patients showed an active CMV infection during the course of the 30-day study period.
CMV reactivation was linked with a longer stay in ICU and hospital, results showed.
Report author Dr Ajit Limaye, associate professor of medicine and laboratory medicine at the University of Washington, said: ‘A substantial number of these patients had CMV reactivate in their bloodstream.
'What's interesting is that having the virus reactivate was associated with longer ICU and hospital stays, independent of other potential variables.’
Journal of the American Medical Association (2008) 300: 413-422