RESEARCH Coronavirus-positive Nasophar yngeal Aspirate as Predictor for Severe Acute Respirator y Syndrome Mor tality Owen Tak-Yin Tsang,* Tai-Nin Chau,* Kin-Wing Choi,* Eugene Yuk-Keung Tso,* Wilina Lim,† Ming-Chi Chiu,* Wing-Lok Tong,* Po-Oi Lee,* Bosco Hoi Shiu Lam,* Tak-Keung Ng,* Jak-Yiu Lai,* Wai-Cho Yu,* and Sik-To Lai* Severe acute respiratory syndrome (SARS) has caused a major epidemic worldwide. A novel coronavirus is deemed to be the causative agent. Early diagnosis can be made with reverse transcriptase-polymerase chain reaction (RT-PCR) of nasopharyngeal aspirate samples. We compared symptoms of 156 SARS-positive and 62 SARS-negative patients in Hong Kong; SARS was con- firmed by RT-PCR. The RT-PCR–positive patients had sig- nificantly more shortness of breath, a lower lymphocyte count, and a lower lactate dehydrogenase level; they were also more likely to have bilateral and multifocal chest radi- ograph involvement, to be admitted to intensive care, to need mechanical ventilation, and to have higher mortality rates. By multivariate analysis, positive RT-PCR on nasopharyngeal aspirate samples was an independent predictor of death within 30 days. Sing infectious disease worldwide. By May 28, 2003, a evere acute respiratory syndrome (SARS) is an emerg- total of 745 patients had died of SARS and 8,240 persons were infected. At the same time, 270 patients had died of SARS and 1,730 were diagnosed in Hong Kong. As defined by the Centers for Disease Control and Prevention (CDC), a suspected SARS patient is a person with a tem- perature >38°C; clinical findings such as cough, shortness of breath, and difficulty breathing, together with history of travel to an area with documented local transmission or close contact with a suspected SARS patient within 10 days of symptoms onset. A probable SARS case also requires radiologic evidence of pneumonia or respiratory distress syndrome or autopsy findings consistent with pneumonia or respiratory distress syndrome without an identifiable cause (1). Because of this nonspecific definition, many non-SARS patients may be mislabeled as having SARS. *Princess Margaret Hospital, Hong Kong; and †Public Health Laboratory Centre, Hong Kong The discovery of coronavirus as the causative agent and the establishment of laboratory tests for coronavirus have aided the research direction. However, these tests only act as supplementary aids to the diagnosis of suspected and probable cases of SARS. The diagnostic tools for coron- avirus infection include reverse transcriptase-polymerase chain reaction (RT-PCR), serologic testing, electron microscopy, and viral culture. A fourfold increase in paired serologic test results suggest highest sensitivity and is regarded as the standard criterion for diagnosis. Studies have shown that antibodies against coronavirus are usually present 14–21 days after onset of symptoms. Electron microscopy and viral culture for coronavirus are specific, but the sensitivity is low. The sensitivity of the RT-PCR for coronavirus in nasopharyngeal aspirate (NPA) samples ranges from 32% to 50% at the beginning of an illness and in stool samples is 97% at a mean of 14.2 days (2,3). The variation in sensitivity makes it difficult for the RT-PCR to be the standard criterion for diagnosis. Though the sensitiv- ity is less than perfect, the assay can be used as a tool for early diagnosis. Until now, no data existed regarding the clinical course and outcome of SARS patients with NPA samples that were positive or negative for coronavirus by RT-PCR. We compared the epidemiologic, clinical, labora- tory, and radiologic differences between RT-PCR–positive SARS and RT-PCR–negative SARS samples. We also looked for possible microbiologic evidence of coronavirus infection in RT-PCR–negative patients. Methods Patients Two hundred sixty-seven patients fulfilling CDC case definition for suspected or probable SARS were admitted to the isolation wards of the Princess Margaret Hospital from February 26, 2003, to March 31, 2003. RT-PCR on Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 9, No. 11, November 2003 1381