The MRT system provides three million rides a day.Tobe effectively germ-free, you would need to wipe down the hand rails with sanitisers every hour, at least. It would be more effective and more meaningful if commuters who feel they are prone to infection wash their hands after each ride.
All air-conditioning and ventilation systems can be breeding grounds for bacteria and fungi because dust and moisture build up. To prevent this, these systems are cleaned regularly, sometimes with a strong chemical. It is in the interest of operators to do this because a clean system is also usually an efficient system.
Are MRT users exposed to more germs than, say, bus, taxi and private car users? I have not come across any study which tests this hypothesis. Commuters who are unwell should avoid packed places, or wear a mask. The same goes for people who are susceptible to catching a bug.
There are, of course, other places which are crowded, such as a stadium, pub or mall. And people tend to spend longer periods in these places than on a train at any one time.
The best way to boost your body’s immune system is to eat healthily, exercise regularly, get plenty of rest, drink plenty of water and avoid negative stress.