The discovery that a novel coronavirus is the probable cause of the newly recognized severe acute respiratory syndrome (SARS), reported by Ksiazek et al. (pages 1953–1966), Drosten et al. (pages 1967–1976), and Peiris et al.¹ provides a dramatic example of an emerging coronavirus disease in humans, described by Poutanen et al. (pages 1995–2005), Tsang et al. (pages 1977–1985), and Lee et al. (pages 1986–1994). Although human coronaviruses cause up to 30 percent of colds, they rarely cause lower respiratory tract disease. In contrast, coronaviruses cause devastating epizootics of respiratory or enteric disease in livestock and poultry.

Most coronaviruses cause disease . . .