Around 1,200 people each year are infected with the hepatitis E virus (HEV) through donated blood in England, a large study shows.
Most people will not notice any symptoms, although it can cause liver damage and be fatal in some cases.
The study in the Lancet medical journal showed one in 3,000 blood donations was contaminated.
Hepatitis E tends to be mild but can be a problem particularly for pregnant women.
A group of researchers from Public Health England analysed 225,000 blood donations in the south-east of England to estimate the scale of the national problem.
Prof Richard Tedder, from Public Health England, said: “[The] infections are widespread in the English population, including blood donors.
“Although rarely causing any acute illness, hepatitis E infections may become persistent in immunosuppressed patients, putting them at risk of future chronic liver disease, and a policy is needed to identify these persistently infected patients and provide them with appropriate antiviral treatment.
“However, our study indicates that the overall burden of harm resulting from transfusion-transmitted HEV is slight.”
He said there was no immediate need to screen donated blood.
However, Prof Jean-Michel Pawlotsky, from the Universite Paris-Est in France, said that stance was “surprising”.
“The potential clinical results of blood-borne HEV infection should not be downplayed, in particular, the risk of serious complications and death exists.
“I believe that systematic screening of blood components for markers of hepatitis E infection should be implemented.”
Lorna Williamson, the medical director for NHS Blood and Transplant said: “These study findings contribute to our overall understanding of hepatitis E and are an important part of the research that helps NHSBT to make blood transfusions as safe as possible for the patients who need them.
“The majority of patients followed up have now cleared the HEV infection and any remaining patients are being followed up.
“We now expect the Advisory Committee on the Safety of Blood, Tissues and Organs (SaBTO), which advises UK ministers and health departments, to review the study results.”
BBC
