Hepatitis infection may increase the risk for Parkinson’s disease, though the reasons for the link remain unknown.

British investigators used records of 100,390 patients hospitalized with various forms of hepatitis or H.I.V. from 1999 to 2011. They compared Parkinson’s incidence in these patients with incidence in more than six million people admitted for medical or surgical conditions like cataracts, knee replacement or varicose veins.

The study, in Neurology, found that people with hepatitis B had a 76 percent higher risk of having Parkinson’s, and people with hepatitis C a 51 percent higher risk, than the control group. Those with other forms of hepatitis or H.I.V. had no increased risk.

The study was restricted to hospitalized patients, and the authors did not have detailed information about the severity and treatment of the diseases.

“We can’t be sure what is underlying this association,” said the lead author, Dr. Julia Pakpoor, a researcher at the University of Oxford. “It could be the treatment for the hepatitis, or it could be that Parkinson’s and hepatitis have common risk factors we haven’t identified.” A different kind of study would be needed, she said, to determine possible mechanisms that might be involved.