There are also suspicions that the first outbreak in the southern Chinese province of Guangdong stopped so abruptly because of the onset of summer. The SARS virus does not survive well in a hot environment, and if most transmission is due to people touching contaminated surfaces, higher temperatures would have reduced transmission.
If the season, rather than human intervention, was the main reason for the end of the outbreak, SARS could return with a vengeance in the autumn. That is what happened with the 1918 influenza pandemic, which killed tens of millions. Fortunately, SARS is far less infectious (so far).