A very large amount of hepatitis C virus in their bodies contributed to, and in some cases, directly caused the deaths of seven of the eight patients who died.
Professor Lim Seng Gee, a senior liver specialist at the National University Hospital (NUH), and a member of the Independent Review Committee, said these patients had an "extremely high" number of viruses in their blood.
All were kidney transplant patients with low immunity because of the immunosuppression drugs they need to take so their bodies do not reject the foreign kidney. One of the patients received the transplant within the past year.
The drug they need to take paralyses the body's immune cells, so the virus can replicate freely in their blood, resulting in much more than what would be found in a normal hepatitis C patient.
Prof Lim said that the amount of viruses they had "goes beyond the upper limit of detection of the kit".
He added that just one drop of their blood would have had at least 5,000,000 viruses.
This was also the reason for the easy transmission of the disease as just a tiny speck would carry a huge number of viruses.
All 25 patients who had the virus had stayed longer in hospital than patients who did not get infected, suggesting that their longer stay exposed them to greater risk. Twenty of them had received a transplant.
The report by the committee found that the primary causes of the eight deaths were infections of the lungs, blood and their transplanted kidneys, as well as end stage kidney failure.
There was definitely no link between one of the deaths and the hepatitis C virus.
Asked if any of the seven patients could still be alive today if they had not been infected by the hepatitis C virus, Prof Lim said: "I think one can always speculate that's the case."
He said that they suffered from jaundice and severe liver dysfunction, which are caused by the hepatitis C virus.
Professor Leo Yee Sin, director of the Institute of Infectious Diseases and Epidemiology at Tan Tock Seng Hospital, and chairman of the review committee, said that the hepatitis C virus "can lead to rapid death in the immunosuppressed", who could suffer from "jaundice, liver failure and death within weeks".
Prof Lim said: "In some of the cases, there were no other co-morbid factors, there was just basically hepatitis C, there was liver failure and it was fairly straightforward."
He added that in all seven, "hepatitis C was definitely a contributing factor, or we certainly could not exclude it as a contributing factor".
This article was first published on Dec 9, 2015.
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