Although severe acute respiratory syndrome (SARS)is highly infectious in clinical settings, SARS has not beenwell examined in household settings. The household andhousehold member attack rates were calculated for 1,214SARS case-patients and their household members, strati-fied by two phases of the epidemic. A case-control analysisidentified risk factors for secondary infection. Secondaryinfection occurred in 14.9% (22.1% versus 11% in earlierand later phases) of all households and 8% (11.7% versus5.9% in the earlier and later phases) of all household mem-bers. Healthcare workers' households were less likely to beaffected. Risk factors from the multivariate analysis includ-ed at-home duration before hospitalization, hospital visita-tion to the SARS patient (and mask use during the visit),and frequency of close contact. SARS transmission at thehousehold level was not negligible in Hong Kong.Transmission rates may be greatly reduced with precau-tionary measures taken by household members of SARSpatients
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