The World Health Organization (WHO) said yesterday an "unlucky" combination of environmental and health factors caused a major outbreak of SARS in one Hong Kong apartment complex where more than 300 people caught the disease.
Leaky sewage pipes and powerful bathroom ventilation fans carried contaminated droplets through parts of a Hong Kong apartment complex, causing one of the world's worst outbreaks of SARS, WHO investigators said yesterday.
More than 300 people came down with the illness at the Amoy Gardens apartment complex in late March, and 35 people died. The speed of the infection amazed health experts, who at the time believed the disease was spread mainly by person-to-person contact.
Hong Kong reported four new SARS deaths yesterday but only three new infections, the lowest number since officials began releasing daily statistics in March. SARS has now infected 1,706 people here and killed 238.
A report written by a team of WHO investigators blamed an "unlucky" combination of circumstances -- a patient with diarrhea, seeping pipes and drafty air shafts at Amoy Gardens. The findings largely confirm an earlier report by Hong Kong officials.
"It's just an accumulation of events," team leader Dr. Heinz Feldmann told a news conference. Feldmann said there was no way to guarantee against a repeat, but that another such outbreak seems "unlikely."
When the WHO investigators went to Amoy Gardens to collect samples, they found no live coronaviruses -- the family of virus believed to cause severe acute respiratory syndrome -- and no remaining genetic material from the virus, Feldmann said.
The WHO team is still conducting lab tests on samples collected from another housing development, the Tung Tau Estate, that suffered a minor outbreak. Feldmann said preliminary findings showed the sewage system did not appear to be the cause there.
The disease was brought to the Block E building of Amoy Gardens by a sick man visiting his brother, the Hong Kong government said earlier. The man had diarrhea and others who caught SARS in the building also developed diarrhea, spreading the virus in the sewage system.
Droplets containing the virus apparently got into some apartment units through dried-out drain traps -- the U-shaped pipes that are supposed to keep gases and waste from coming up back up. Exhaust fans in the bathrooms sucked the droplets into apartments, the WHO report said.
The exhaust fans could also have moved contaminated droplets into a light and air shaft, where wind may have carried them into other apartments through open windows.
"The fans are, in a lot of apartments, far too powerful. They would serve an area sometimes that are 10 times as big," Feldmann said.
Hong Kong Deputy Health Director Dr. Leung Pak-yin said the government will closely study the WHO report and make suggestions to the public as to what types of exhaust fans are suitable for their apartments.
Feldmann said there was no evidence the virus itself was airborne, but small droplets can travel up to 1.5m through the air, perhaps further if helped by a strong wind.
A break in a pipe shut down the water used to flush toilets at one point, which may have trapped some infected sewage in place and allowed the virus to multiply, the team said.
Feldmann said an earlier outbreak of SARS at Hong Kong's Metropole Hotel appears to have been caused by close person-to-person contact.