Two SMRT train drivers and one crew manager have contracted tuberculosis (TB).
The Straits Times understands that the three - from Tanah Merah station - were diagnosed four to six weeks ago. Two were found to have latent TB, and the other was found to have active TB. Latent TB is not contagious, but can develop into contagious active TB if untreated.
SMRT has since carried out TB screening for its Tanah Merah personnel, but it is not known how many have been tested. Results of the screening will be out in a couple of weeks, according to sources.
SMRT spokesman Patrick Nathan said the firm, after finding out about the active TB case, worked closely with the authorities to carry out contact tracing and this is ongoing. The other two cases are not linked to the active TB one, he added.
He also said that "SMRT has also carried out extensive sanitisation of staff work areas. SMRT takes healthcare concerns very seriously and will spare no effort in taking the necessary steps to keep our staff and commuters safe."
When contacted for comment, the Health Ministry said TB was not easily transmitted. A spokesman said: "The risk of transmission to persons who are not close contacts of a TB case - for example, through casual, brief contact - is very low. Screening is thus generally not necessary for commuters should public transport staff be infected."
Dr Asok Kurup, an infectious disease specialist at Mount Elizabeth Hospital, said: "The degree of infectiousness depends on the severity of symptoms. If someone has minimal symptoms, we don't expect them to be posing much risk."
Asked if drivers or passengers should wear masks, Dr Kurup said only N95 masks - the heavy-duty sort used during the haze season - would be effective. But he added that such a measure was not commensurate with the risk.
Another infectious disease specialist, Dr Wong Sin Yew, concurred that the risk faced by commuters "is likely to be low".
"I do not expect that there will be any direct contact between commuters and train drivers," he said. "Even if there was, it is expected to be trivial, transient and lasting for seconds to minutes."
Meanwhile, commuters had mixed responses when asked if they would get on a train with a driver who might have TB.
Ms Catherine Ng, 39, a director of a real estate firm, said: "I would, but I would take some precautions like wearing a mask, and not going near the driver."
Retiree Anthony Ng, 66, said: "You will never know if someone has TB, because they don't wear a card to say they have TB. But if I knew, I would not take the risk."