Victoria's acting chief health officer says the risk to patients treated by a healthcare worker infected by hepatitis B is less than one per cent.

Victoria's top health officer says the chance of someone contracting hepatitis B from an infected Melbourne healthcare worker is less than one per cent.

The Department of Health and Human Services is contacting 654 patients in Melbourne following the diagnosis of hepatitis B in the health worker.

"(But) my professional judgment here is that the risk is going to be less than one per cent and that's based on historical investigations of this nature in other countries," acting chief health officer Dr Roscoe Taylor told 3AW on Thursday.

Hepatitis B is a blood-borne virus spread through unsafe sex with an infected person and less frequently through blood-to-blood incidents such as needle stick injuries.

Dr Taylor said there had been a methodical examination to determine all the patients the health worker had been in contact with over the past three years.

"The heartening thing at the moment is so far there haven't been any hepatitis B notifications (in the group of patients) for that period of contact with the health worker," the acting chief health officer said.

The department is arranging for all 654 patients to have a blood test to rule out the presence of hepatitis B.

They started receiving letters earlier this week.

Only patients who have been contacted directly by the department need to take any action, Dr Taylor said in a statement.

Healthcare workers are obliged to know their own blood-borne virus status and declare it to authorities every year.

Most health facilities also require staff to be vaccinated against hepatitis B.

Dr Taylor said if a worker knew they had a virus and failed to disclose it "that is professionally inappropriate and it should not happen".

*People wanting information or support in relation to viral hepatitis can contact Hepatitis Victoria's infoline on 1800 703 003.