EMERGENCE OF SARS case-patients in Hong Kong compared with case-patients in the United States may have also altered the pattern of shedding of SARS-CoV. Persistent respiratory symptoms that were reported up until at least 2 months after onset by most of our case- patients were similar to symptoms observed by Avendano et al. (19) in a study of Canadian healthcare workers who were followed for 5 weeks after illness onset, suggesting residual illness in SARS case-patients. However, the pro- gression of these symptoms over time is difficult to inter- pret without a better appreciation of the pre-illness symp- toms. Antibody to SARS-CoV in some case-patients was documented as early as day 10 after illness onset. We did not have an adequate number of early serum specimens from other case-patients to determine when SARS-CoV antibody is first detectable. Results of this investigation should be interpreted in light of several limitations. The small number of partici- pants does not allow for accurate estimation of the risk for transmission to household members. Irregular and long intervals between collections of specimens do not permit a clear picture of the natural history of SARS-CoV infection, including documenting the precise timing of the first appearance of SARS-CoV antibody. We also may have missed the presence of shedding in stools of other case- patients who had reported diarrhea during the acute phase of illness. Possible variations in specimen collection and handling techniques could also have affected SARS-CoV detection rates in respiratory and stool specimens. Our results suggest that SARS-CoV is not always trans- mitted efficiently. Routine collection and testing of stool and sputum specimens of probable SARS case-patients may help the early detection of SARS-CoV infection. A follow-up of recovered SARS case-patients over several months would also help to better assess possible waning of antibody titers and long-term sequelae of the disease and, thus, improve our understanding of the true illness associ- ated with SARS-CoV infection. Acknowledgments We thank all patients and their family members who partic- ipated in this investigation. We also thank D. Vugia, G. Rothrock, L. Santos, E. Quiroga, the California-Los Angeles Public Health Laboratory, California-Long Beach Public Health Laboratory, California-San Diego Public Health Laboratory, H. Meyers, K. Coy, S. Dunn, F. Schwartz, C. Perry, P. Habibi, D. Walsh, C. Sullivan, S. Meyers, C. Norman, A. Han; W. Dunlap, K. McGahagin, M. Anand, D. Weber, K. Dail, L. Albers, M. Eilerman, F.Alvarez, L. Rider, A. Kelley, J. Monroe, M. Craig, J. Osthues, G. Prakalapakorn, C. Qi, S. Bo, Q. Doan, and F. Gao. 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