Study Booth et al (2003)N = 144, confirmed casesRetrospective study Choi et al (2003)N = 267 (227 confirmed cases)Retrospective study Zou et al (2004)N = 165, confirmed casesRetrospective study Chan et al (2004)N = 669, (323 tested positive)Clinicopathologic study Huang et al (2004)N = 78, probableRetrospective study Ding et al (2004)N = 8 (4 confirmed cases, 4 control)Clinicopathologic study Chu et al (2005)N = 536, confirmed casesRetrospective study