Incidence and Characteristics of Viral Community-Acquired Pneumonia in Adults

This study was a prospective observational study of all adult patients admitted to Christchurch hospital in New Zealand from July 1999–July 2000 with the diagnosis of community-acquired pneumonia (CAP). CAP was defined as an acute illness with radiographic pulmonary shadowing that was at least segmental or present in one lobe, and was neither pre-existing or of known cause. Exclusion criteria included if pneumonia was not the main reason for admission, was an “expected terminal event,” was distal to a bronchial obstruction, or was associated with bronchiectasis or known tuberculosis. Laboratory evaluation included blood and sputum cultures, urine tested for Streptococcus pneumoniae and Legionella pneumophilia antigens, and nasopharyngeal swabs for viral immunofluorescence, viral culture, viral serology, and polymerase chain reaction. Viral infection was diagnosed when a respiratory virus was detected in nasopharyngeal samples or there was detection of a fourfold or greater rise in reciprocal antibody titers to a respiratory virus when testing paired serum samples. Bacterial pneumonia was diagnosed when blood or good-quality sputum samples were positive. S. pneumonia and L. pneumophila were also diagnosed if antigen was detected in urine or there was detection of a fourfold or greater rise in reciprocal antibody titers, Mycoplasma pneumonia if reciprocal IgM titers were elevated, and Chlamydia pneumonia if reciprocal antibody titers were elevated. Of 304 patients admitted with CAP, only 199 subjects got the “full battery” of testing. A microbiological cause could be determined in only 177 patients, and of those, a viral diagnosis was made in 88. Forty-five patients had mixed bacterial and viral etiologies, with Rhinovirus and Influenza A the most common viruses cultured. Myalgias were associated with any respiratory viral infection, neutrophilia with Rhinovirus specifically, and rigors and smoking history with pneumococcus. Increasing age, male gender, and mixed rhinovirus/pneumococcal infection were independently associated with severe disease. The authors concluded that viral CAP is common in adults, and that the prevalence of both viral and bacterial etiologies is likely underestimated. They hypothesize that there is likely frequent viral and bacterial co-infection and that the presence of rhinovirus with pneumococcus may increase disease severity.