Toilet Flush May Have Spread SARS

Hong Kong study calls for better look at airborne transmission

WEDNESDAY, April 21, 2004 (HealthDayNews) -- A new study suggests that severe acute respiratory syndrome (SARS) may have been spread through the simple act of flushing a toilet instead of being passed directly from person to person.

Even with all the research that has been conducted on SARS in the past year, some mystery still remains as to how the virus can be transmitted.

Two articles appearing in the April 22 issue of the New England Journal of Medicine explore the possibility of airborne and laboratory transmissions. Both scenarios point to new public health measures that should be taken to contain the disease.

"Airborne spread of a concentrated source of virus can infect many persons within a short period of time," Dr. Tak-sun Ignatius Yu, lead author of one of the studies and an associate professor of community and family medicine at the Chinese University of Hong Kong, said. "Future prevention and protection against SARS should take into consideration the possibility [that] airborne transmission avoidance of close contacts alone may not be adequate. The prevention of aerosolization of the virus source should take priority."

Yu and his co-authors conducted an analysis of the outbreak at Amoy Gardens, an apartment complex in Hong Kong where more than 300 residents were affected last year when the SARS epidemic hit a number of Asian countries before spreading elsewhere in the world.

The study reads more like an architectural or building treatise than a medical paper, with detailed descriptions of floor plans, bathroom drains, wind flow, and more.

The authors conclude that an earlier World Health Organization (WHO) report was at least partly correct. It appears that the "index patient," the one who introduced the disease to the compound, used the bathroom in unit 7 on a middle floor of Building E on March 14 and March 19, 2003. That individual's feces later turned out to have a very high concentration of SARS coronavirus.

WHO investigators had already noted that many traps in bathroom floor drains were dried out, meaning an exhaust fan could have drawn droplets, or aerosols, from the drainage pipe into the bathroom and then into an air shaft. From there, the contaminated air plume could have been carried upward by the natural air current and into other apartments.

When they constructed a model of the drainage system, the study authors found that large number of aerosol particles were drawn out by the flushing of the toilet.

"If the toilet overflows, you want it to go somewhere, so it makes sense to put drains in apartment buildings, but in this case it was a vulnerability," added Dr. Donald K. Milton, co-author of an accompanying perspective article and a lecturer at the Harvard School of Public Health in Boston. "One wonders if this is a pathway that we just have never noticed before, because it didn't hit us over the head the way it did in this case. But it's always been there in the background steadily doing something, and that's something interesting to speculate about."

Still, this does not explain how the virus traveled to different buildings. The authors postulated that horizontal air movement between buildings and northeasterly winds may have been responsible.

Even if the particles were airborne, specific circumstances would still need to come into play, they said.

"We need a large concentrated dose of the virus source, a mechanism [for] dispersing the source into fine aerosols, which can be suspended in air for a long period of time, and the appropriate weather and wind conditions and topography so the virus could be spread to a large number of people in a short period of time (before the viruses die off)," Yu explained. "In the community, the combination of these specific circumstances may not be common. However, aerosolization of the virus source is not uncommon inside hospitals, and the ventilation systems inside many general hospitals or wards are not particularly helpful in removing the virus-laden aerosols once they are generated."

The findings, Milton argued, are a reason to resurrect the field of airborne transmission, which has lain fallow for half a century. "There's a lot of new technology around in that 50 years, and we ought to be able to make some advances if we put some thought to this -- and this was a wake-up call," he said.

Milton added, however, that the findings do not make SARS any more contagious than it was before.

The study noted, however, that several workers in the Amoy complex, who would have come into contact with infected people, were not sickened.

The second study appearing in the journal looked at the case of a lab worker with no apparent exposure to SARS and no travel history who nevertheless contracted the disease after the outbreak was over in late May 2003.

The patient, a 27-year-old graduate student in microbiology, had been working with a vial of West Nile Virus which later turned out to be contaminated with SARS. Exactly how the transmission took place is not clear.

"We think the evidence would indicate that the patient was infected from a vial that contained both viruses," said Dr. Poh-Lian Lim, lead author of the study and a consulting physician in the department of infectious diseases at Tock Seng Hospital in Singapore. "We are not sure exactly how he acquired SARS, but the most likely route was via the respiratory tract (as opposed to percutaneous exposure like a needlestick)."

The bottom line, Lim added, is that laboratory exposure is a potential risk for getting infected, and measures need to be taken to prevent this from happening.

According to the latest World Health Organization figures, between Nov. 1, 2002, and July 31, 2003, SARS hit 28 countries, sickening 8,096 people and causing 774 deaths.

More information

Find more on SARS at the U.S. Centers for Disease Control and Prevention or the World Health Organization.

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