"Super-spreaders", who survive the disease but are highly infectious, are one possibility. A young Singaporean woman is now believed to be linked to virtually all of that country's 130 cases.
New information has also emerged from the investigation of the Amoy Gardens housing complex in Hong Kong, where 200 resident caught SARS. The virus was found in basins and toilets, say officials, suggesting the virus travelled through the clogged sewage system. Malik Pieris, head of virology at the University of Hong Kong, also reports that tests show the virus can survive in faeces.
I believe Legionarres Disease was known to spread through plumbing also.