Viral Infection in Community-Acquired Pneumonia Is Common

Key Point

Viral etiologies of community-acquired pneumonia (CAP) are poorly characterized, even as CAP incidence appears to be increasing. However, comprehensive microbiological assessment of CAP patients revealed some interesting findings.

Globally, viral community-acquired pneumonia (CAP) has sparked interest in recent years, noted Lance Jennings, PhD, and colleagues from Christchurch Hospital in New Zealand in the January Thorax. Among the reasons for this renewed interest are the recent outbreaks of SARS and human cases of H5N1 influenza infection. Nevertheless, viral etiologies of CAP in adults have been poorly defined compared with those of bacterial CAP, often due to limited use of available diagnostic tools.

In their study, Dr. Jennings and colleagues identified pathogens involved in CAP using an array of microbiological tests in hospital patients 18 or older who had an acute respiratory illness with radiographic pulmonary shadowing in at least one segment or lobe.

They found that about one-third of adults hospitalized for CAP have a viral infection. Included among the tests were blood and sputum cultures, urinary antigen testing for Streptococcus pneumoniae and Legionella pneumophila, antibody detection in paired sera, and detection of respiratory viruses in nasopharyngeal swabs by immunofluorescence, culture, and polymerase chain reaction (PCR).

“This is one of few studies to use such a comprehensive battery of viral diagnostic tests in order to detect respiratory virus infection in adults with CAP,” the researchers noted. Patients whose main reason for admission was not pneumonia, those for whom pneumonia was an expected terminal event, and those with pneumonia that was distal due to bronchial obstruction, bronchiectasis, or tuberculosis were excluded from the analysis.

CAP ETIOLOGY

Beyond identifying specific pathogens, the investigators sought to determine if clinical characteristics were associated with particular organisms and if clinical markers of viral pneumonia could be recognized. Disease severity was assessed through use of the
CURBage score (confusion, urea, respiratory rate, blood pressure, age; severe disease defined as a score of ≥ 2) and the Pneumonia Severity Index (PSI; severe disease defined as risk class IV or V).

Viral infection was diagnosed when a respiratory virus was detected in nasopharyngeal samples by immunofluorescence, culture, and/or PCR, and/or when there was a fourfold or more increase in reciprocal antibody titers using paired samples. Pneumococcal infection was diagnosed when S pneumoniae was isolated from blood and/or good quality purulent sputum.

Of 304 patients, etiology was established in 177 (58%) and viral diagnosis in 88 (29%). Two or more pathogens were found in 49 (16%) patients, with 45 of those having mixed viral-bacterial infections.

Immunofluorescence detected 11 viruses, culture detected 32, serology detected 44, and PCR, 52. For influenza A and B, adenovirus, parainfluenza, and respiratory syncytial virus, PCR added “little extra to the diagnostic yield”; only two cases were detected by PCR alone.

However, for rhinovirus and the coronaviruses, only PCR yielded positive results. Throat cultures obtained from a control group of 50 patients confirmed that rhinovirus PCR positivity was true infection and not merely a coincidental finding.

Logistic regression analyses were performed to:

· Identify associations between type of infection and characteristics on
admission
· Determine whether particular organisms or patient characteristics were independently associated with severe disease.

Analysis of any viral, influenza, rhinovirus, and pneumococcal infection took into consideration age, symptom duration, influenza season, myalgia, rigors, influenza vaccination within a year, current smoking status, and neutrophilia. CURBage scores and PSI risk class were evaluated separately; both models included age; male sex; presence of comorbidity; smoking status; radiographically confirmed multilobe disease; rhinovirus, influenza, or pneumococcal infection; and influenza vaccination within the past year.

In patients with viral disease, diabetes was more common, severe disease was less common, and duration of symptoms before admission was longer than in patients with pneumococcal pneumonia. For both the CURBage and the PSI assessment tools, increasing age, male sex, and mixed rhinovirus/pneumococcal infection were independently associated with severe disease. Myalgia was associated with any respiratory virus and influenza pneumonia. Influenza vaccination was associated with a reduction in influenza pneumonia and any viral pneumonia during the flu season.

CLINICAL IMPLICATIONS

In this study, about one-third of patients with identifiable pathogens had pneumonia caused by one or more viruses—a higher rate of detection than in several previous studies not using nucleic acid amplification assays, noted the authors. Adding PCR seems to increase the likelihood of finding viruses. While the optimal environment for rhinovirus replication is between 33?C and 35?C—lower than core body temperature—rhinovirus is increasingly implicated in lower respiratory tract infections, the investigators added.

Dr. Jennings told Pulmonary Reviews, “Respiratory viruses are increasingly being recognized as playing an important role in severe lower respiratory tract infections in adults and may have a role in initiating disease. The application of comprehensive viral testing has extended this understanding. However, the role of viruses—especially that of mixed pneumococcal/rhinovirus infections—needs to be further elucidated to allow recommendations to be made on the use of routine comprehensive viral testing in these patients.”           

—Beth Tansey Peller, RN

Suggested Reading
Jennings LC, Anderson TP, Beynon KA, et al. Incidence and characteristics of viral community-acquired pneumonia in adults. Thorax. 2008;63(1):42-48.
Lim WS, van der Eerden MM, Laing R, et al. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax. 2003;58(5):377-382.
Mandell LA, Bartlett JG, Dowell SF, et al. Update of practice guidelines for the management of community-acquired pneumonia in immunocompetent adults. Clin Infect Dis. 2003;37(11):1405-1433.

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