Abstract: Objective To explore understand the characteristics of transmission of severe acute respiratory syndrome(SARS), analyze the possible factors of influencing transmission in families and to provide scientific evidence for formulating strategies of SARSprevention and control.Methods Acase-control study was conducted in Xicheng District and Haidian District of Beijing in 2004.The case was defined as a household with two or more cases of SARSand control was defined as that with only one case.All the patients were interviewed with an ad hoc questionnaire, to compare the difference of factors that influenced transmission of SARSin families, including demographic data, exposure information(time, frequency and mode), occurrence of SARSin contacts(number and time of onset), economic status, hygenic behavior, and so forth.Results There was no significant difference in living space between 56 cases and 47 controls(t=0.82, P=0.41).Proportion of families with more than three members living together was 35.71% in cases, higher than that in controls(26.09%), and proportion of families with more than two members living in a room was 38.89% in cases, also higher than that in controls(30.43%), but no statistical significance between the case and control.After onset of fever, 83.93% of the patients worried about whether they suffered from SARSin cases, significantly higher than that of 16.07% in controls(P<0.05).More than 80 % of the patients would visit hospital when they had fever.About 90% of the patients thought they infected SARSfrom hospitals both in cases and controls, and 10.71% of them infected from families in cases and 8.51% in controls(P<0.05).Room disinfection was carried out in 40.43 % of the families with the patients after occurrence of fever in cases, but only 21.82% in controls, and tableware were not shared in among family members in 44.68 % of controls, but only 25.45% in cases(P<0.05).No effects of wearing gauze masks while communicating with others, no dining with others together, as well as taking traditional Chinese herbal medicine and immune-enhancing agents on prevention of SARStransmission were found in this study.Conclusion Less persons living together in a family or in a room can reduce SARStransmission in families.Self-isolation and disinfection are beneficial to reduction of SARStransmission in families after occurrence of fever.No evidence showed that traditional Chinese herbal medicine and some immune-enhancing agents can significantly prevent transmission of SARSin families.

Key words: severe acute respiratory syndrome, case-control study, transmission in families, questionnaire