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Ling JM, Shaw PC, Kam KM, Cheng AF, French GL.Ling JM, et al. Among authors: cheng af.Epidemiol Infect. 1993 Jun;110(3):437-46. doi: 10.1017/s095026880005086x.Epidemiol Infect. 1993.PMID: 8519309Free PMC article.