PUBLISHED : Friday, 09 May, 2003, 12:00am
UPDATED : Friday, 09 May, 2003, 12:00am

There has been concern about the transmission of the Sars virus through contaminated sewage systems and the use of contaminated toilets in the Amoy Gardens cluster of cases.

Now the WHO has confirmed that coronavirus can survive in human excrement for about four days and that convalescent patients shed the virus in their excrement for weeks. The experts have further warned that since the virus survives in sub-zero temperatures indefinitely, it might in all probability re-emerge next spring.

To most people, the term toilet transmission conjures up a scenario of finger-soiling and transferring the virus to food, but few are aware of the role of aerosol (droplets and airborne particles) churned up by flush systems.

There are currently two main toilet-flushing systems. One system uses water cascade and the other whirlpool.

The cascade system generates a lot of noise and a tremendous quantity of aerosol, as was proven by Japanese scientists four to five years ago.

The whirlpool system is quiet and generates much less aerosol - one should consider this when buying a toilet.

If an infected user contaminates a toilet bowl, the next user may get the virus through aerosol inhalation, whether he flushes before or after use. Closing the toilet lid may help, but note the lid is not airtight. The government advisory on this precaution notwithstanding, transmission through public toilets is very important in the prevention and containment of Sars and other respiratory viruses shed by patients in their urine or faeces during convalescence.

Many people use a public toilet every day. Think of this mode of cross-infection in a hospital, even in staff toilets.

Many old residential premises are in need of repair, their sewerage faulty and plumbing dysfunctional. The hind section of the water seal in the toilet elbow communicates freely with the common sewage drain of the premises.

Pathogenic microbes may contaminate the drains and spread vertically again in the next pneumonia season. Since 20 per cent of Sars cases defy contact tracing, this transmission mode could be more significant than we have realised.

I suggest all public hospitals change their toilets to the whirlpool type to prevent cross-infection among frontline medical workers, whose infection rate has been scandalous and a major public concern.

In future, the building ordinance should mandate the installation of whirlpool toilets in all public residential towers and all public toilets.