The discovery that severe acute respiratory syndrome can spread through sewage systems raises new concerns that the virus may have become more virulent and harder to control, according to health officials.
Hong Kong's health secretary, Dr. Yeoh Eng-kiong, said this week that sewage is responsible for SARS infecting 321 people at the Amoy Gardens high-rise apartment complex in Hong Kong. She said ventilation fans sucked particles of the virus out of a faulty sewage system and spread it throughout the building.
The disease moved so rapidly from person to person that some experts believe the virus might be more virulent when spread through fecal matter as opposed to the more commonly reported method: droplets emitted by sneezes or coughs. That would mean investigators have one more route of infection to monitor as they battle the deadly disease.
"If the virus is really different at Amoy Gardens -- if the rate (of transmission) is considerably higher -- that would indicate that things could get difficult," said Dr. Henry Niman of Harvard Medical School.
Health officials have reported that SARS patients who live in Amoy Gardens are coming down with particularly virulent cases of the disease, as are health-care workers who have caught the virus from those patients.
Twenty percent of Amoy victims needed intensive care, compared with about 10 percent of other SARS patients in Hong Kong, said Yuen Kwok-yung, a microbiology professor and co-director of science at the University of Hong Kong Queen Mary Hospital.
"These cases lead us to believe that maybe the virus itself has changed," said Kwok-yung.
The symptoms of Amoy Gardens patients differ from the symptoms of other SARS patients in that a large percentage of Amoy Gardens patients developed intestinal problems.
Sixty-six percent of SARS patients from the apartment complex had diarrhea, compared to up to only 7 percent of previous cases, according to the World Health Organization.
About 50 percent of SARS patients in a Canadian study (PDF) published in the New England Journal of Medicine also had diarrhea. As in Hong Kong, the virus in Canada, which has infected 126 people and killed 12, has been more virulent than in the United States. But researchers have not determined whether diarrhea contributed to the greater virulence of the disease in either Canada or Hong Kong.
SARS has infected 3,389 people worldwide and killed 170, according to the World Health Organization.
Reviewing the Amoy Gardens cases, Niman suggested that sewage might have the ability to transmit larger amounts of the virus, causing more severe symptoms.
But Yuen said it's also possible the virus has mutated to become more virulent.
Researchers in Hong Kong have decoded the genome sequence of one sample of the virus. But it was collected long before the Amoy Gardens outbreak. Scientists in Canada, the United States and Singapore have also decoded SARS genomes. They all appear to be almost identical.
Public health officials in Hong Kong traced the Amoy Gardens outbreak to a 33-year-old man from Guangdong province in China, where the SARS outbreak began. He visited his brother in the apartment complex, and developed SARS symptoms, including diarrhea on March 14.
The building contains many small apartments. The close person-to-person contact in these residences and in public areas such as elevators have contributed to spread of the infection, Hong Kong's health secretary said. Cockroaches and rats may have also helped transmit the virus.
Investigators had found evidence of the SARS virus in fecal matter previously, but this was the first proof that the virus can spread through sewage.
The high-rises contain 33 floors with eight apartments per floor. The effluent from each building is collected in eight vertical "soil stacks" that are separated from the toilets, bathtubs and other plumbing by a U-shaped water trap, which prevents foul smells and insects from entering the plumbing.
However, the water traps must be filled with water in order to work properly, and an investigation by Hong Kong health authorities found they had dried out.
Tenants had been complaining about foul smells in their bathrooms. The faulty traps apparently allowed sewage particles to escape and seep into the bathrooms. Exhaust fans then sucked the particles through the pipes and circulated them through the air.
Experts say it is unlikely that SARS would spread through sewage in the United States as it has done in Hong Kong.
"In North America we have the best sanitary systems anywhere, and we have great public health here," said Barbara Robinson-Dunn, technical director of Microbiology at the William Beaumont Hospital in Royal Oak, Michigan. "One of the keys to public health is (proper handling of) bodily waste."
Meanwhile, in the United States, the Centers for Disease Control and Prevention adopted a more stringent definition of what constitutes a SARS case. That change reduced the number of probable cases to 35.
The CDC previously listed 208 Americans from 34 states as possible SARS cases, but many had only mild flu-like symptoms, and only one-quarter of them were hospitalized.
Reuters contributed to this report.
