How other possible sources of infection were ruled out

Visitors at the entrance of Block 4 at SGH.
Visitors at the entrance of Block 4 at SGH. ST PHOTO: ALICIA CHAN

Q: The Independent Review Committee has said poor infection control measures were behind the hepatitis C outbreak. How did it rule out other possible sources of infection?

A: Apart from poor infection control, the committee looked at three other possibilities - drug diversion, intentional harm and a contaminated batch of products.

First, there were no missing narcotics or other drugs with the potential for abuse in the affected wards.

About 319 nurses, doctors and renal coordinators who had come into contact with patients in the affected wards were screened for the virus to rule out drug diversion or intentional harm. All of them, including those who had left the hospital but returned for screening, tested negative.

The Criminal Investigation Department also looked into the possibility of intentional harm by a staff member, but found no evidence to support this hypothesis.

The report said only 13 of the 25 cases were given medication from at least one vial. The committee concluded that multi-dose medication alone cannot fully explain the transmission of hepatitis C to all 25 cases in the outbreak.

Lastly, 0.9 per cent saline solution was the only product used in common among all the infected patients. However, the review committee noted that this solution is widely used across hospitals, and that more cases of hepatitis C infection should have emerged had the batch of solution been contaminated.

It also sampled 10 random bottles of solution from Ward 67, none of which tested positive for the hepatitis C virus.

Q: What about the multi-dose vials that were suspected to be the cause of transmission of the virus?

A: The report said only 13 of the 25 cases were given medication from at least one vial.

The committee concluded that multi-dose medication alone cannot fully explain the transmission of hepatitis C to all 25 cases in the outbreak.

Q: Was the outbreak from a single source?

A: It seems likely. Detailed analysis by the Agency for Science, Technology and Research and the Duke-NUS Graduate Medical School found that the 25 cases were tightly clustered and closely linked.

The earliest infected case was likely to have been a kidney transplant patient who was not previously diagnosed with hepatitis C, and who was admitted to Ward 64A in early March, then re-admitted in mid-March.

Residual blood samples from mid-March showed that the patient had a high viral load, with at least one million copies of the virus in one millilitre of his blood. In contrast, people who are not infected by hepatitis C have "undetectable" viral loads.

It is not known where this earliest infected case acquired the hepatitis C infection.

Linette Lai

A version of this article appeared in the print edition of The Straits Times on December 09, 2015, with the headline 'How other possible sources of infection were ruled out'. Print Edition | Subscribe