Yield of sputum for viral detection by reverse transcriptase PCR in adults hospitalized with respiratory illness

Diagnostic tests for respiratory viral infections have traditionally been performed on nasopharyngeal swabs or washings. Reverse transcriptase PCR (RT-PCR) is rapid, sensitive, and specific for viral infection diagnosis but is rarely applied to sputum samples. Thus, we evaluated the diagnostic yield of RT-PCR for detection of nine virus types by the use of nose and throat swabs (NTS) and sputum samples from patients admitted to the hospital with acute respiratory tract illnesses. Adults hospitalized with acute respiratory tract illnesses were recruited during the winters of 2008 and 2009. At enrollment, combined nose and throat swabs and sputum samples were collected for RT-PCR for detection of nine common respiratory virus types. A total of 532 subjects admitted for 556 respiratory illnesses were enrolled. A total of 189 virus strains were identified. The diagnostic yields for detection of any virus were 23% (126/556) for NTS RT-PCR and 36% (146/404) for sputum RT-PCR. A total of 83 (44%) of 189 viral detections were positive by both methods, 43 (23%) were positive by NTS alone, and 63 (33%) were positive only with sputum samples. The inclusion of RT-PCR performed with sputum samples significantly increased the diagnostic yield for respiratory viral infections in adults. Further studies designed to adapt the use of sputum samples for commercial RT-PCR respiratory virus assays are needed.