Two more patients who tested positive for hepatitis C have been confirmed as belonging to the same cluster of 22 patients previously discovered to be infected from the same source, said the Singapore General Hospital (SGH).

A third patient tested positive for the virus last Thursday.

"Phylogenetic studies done for the two patients... showed that they are part of the affected cluster, bringing the total number of affected patients to 25," said Professor Fong Kok Yong, chairman of the hospital's medical board.

Both patients were admitted to the hospital between April and June this year. They were contacted by SGH as part of its screening of patients who had stayed in wards 64A and 67 from January to June.

It announced on Oct 6 that 22 kidney patients had contracted hepatitis C while receiving treatment in the hospital. Of the 601 patients screened so far, 586 have tested negative for the virus. Three tested positive, while the results of 12 are pending. Eight patients died, with five of the deaths possibly linked to the infection.

SGH added that a total of 309 staff have been screened, all of whom tested negative. An independent review committee has been set up to investigate the spread of the hepatitis C virus in the hospital.

Last week, two international experts were invited to the committee to provide advice on the analyses, interpretation and reporting of the findings.

The hospital's own review committee completed its investigation of the last patient death last Tuesday. SGH also filed a police report last Tuesday in order to rule out any possibility of foul play.