Prevalence of respiratory viruses and Mycoplasma pneumoniae in sputum samples from unselected adult patients.

Sputum samples from adult patients are routinely used for bacteriological tests, but not for the diagnosis of viral/mycoplasmal infections. We examined 511 sputum samples submitted for bacterial tests from patients at the Royal Adelaide Hospital. Each specimen was tested directly (and after six days of cell culture amplification) for antigens to influenza A and B, parainfluenza 1, 2 and 3, adenovirus, respiratory syncytial virus (RSV) and Mycoplasma pneumoniae. Respiratory viruses or M. pneumoniae were found in 11% of all specimens but were most common (14%) in sputa reported as containing only "oral flora". Respiratory virus or M. pneumoniae infection was significantly more common in medical patients (12%) than in surgical patients (5%), and was most common in oncology (hematology/radiotherapy) patients (25%). Influenza A and RSV were equally common in medical patients, while RSV was the most frequent isolate in oncology patients. Respiratory viral infection is an underdiagnosed condition in adults, particularly the immunocompromised, which can be successfully diagnosed by virological examination of sputum.