SARS: clinical features and diagnosis

Severe acute respiratory syndrome (SARS) is a highly infectious disease with a significant morbidity and case fatality. The major clinical features include persistent fever, chills/rigor, myalgia, malaise, dry cough, headache and dyspnoea. Less common symptoms include sputum production, sore throat, coryza, dizziness, nausea, vomiting and diarrhoea. Older subjects may present with decrease in general well-being, poor feeding, fall/fracture and delirium, without the typical febrile response. Common laboratory features include lymphopenia with depletion of CD4 and CD8 lymphocytes, thrombocytopenia, prolonged activated partial thromboplastin time, elevated D-Dimer, elevated alanine transminases, lactate dehydrogenase and creatinine kinase. The constellation of compatible clinical and laboratory findings, together with the rather characteristic radiological features especially on HRCT and the lack of clinical response to broad-spectrum antibiotics, should quickly arouse suspicion of SARS. The positivity rates of urine, nasophargyngeal aspirate and stool specimen have been reported to be 42%, 68% and 97%, respectively, on day 14 of illness, whereas serology for confirmation may take 28 days to reach a detection rate above 90%. Recently, quantitative measurement of blood SARS CoV RNA with real-time RT-PCR technique has been developed with a detection rate of 80% as early as day 1 of hospital admission but the detection rates drop to 75% and 42% on day 7 and day 14, respectively.