Nearly a third of hospitalized COVID-19 patients in the United States suffered from some type of altered mental function, and their mortality rate was close to seven times higher than those who didn't experience such problems.

This is according to a study of 509 patients hospitalized in Chicago's Northwestern Medicine health system between March 5 and April 6 published on Monday in the Annals of Clinical and Translational Neurology.

Citing the paper, The New York Times(NYT) said patients suffering from altered function, or "encephalopathy," could experience problems with attention and concentration, loss of short-term memory, disorientation and a coma-like level of consciousness.

Only 32 percent of the patients were able to handle routine daily activities like cooking and paying bills after they were discharged, in contrast to 89 percent of patients not suffering from encephalopathy.

The encephalopathy patients stayed three times as long in the hospital compared to their counterparts and were nearly seven times as likely to die.

The paper, however, did not identify a cause for encephalopathy.