"Some viruses can be air-borne," Dr Yeo explained. "It may be a small chance, but spit is just bad for the general hygiene of the place."

National University Singapore sociologist Tan Ern Ser cites ignorance, bad habits and convenience as reasons that people spit, despite many health campaigns and enforcement.

But do some people even realise that spitting is ungracious?

Dr Tan said: "Most people do, but some don't realise and some don't care."

And what would deter these people from spitting?

Dr Tan had two solutions: education and enforcement.

Sars victims

33 - Number of people who died from Sars in Singapore in 2003. 238 were infected in the same year.

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