Viruses and lower respiratory tract infections: does more mean worse?

issue of Respiration, Gencay et al. [1] used serology for a panel of 8 common human viruses (adenovirus, enterovirus, influenza viruses A and B, parainfluenza viruses 1, 2 and 3, and respiratory syncytial virus) to document evidence of acute viral infection in patients diagnosed with LRTI. Major endpoints studied included: comparison of the proportion of individuals showing positive viral serology between LRTI patients and healthy control subjects; associations of specific viruses with different clinical variants of LRTI (community-acquired pneumonia vs. acute bronchitis vs. acute exacerbation of chronic obstructive pulmonary disease); and whether viruses were associated with concomitant bacterial infections. The results showed evidence of viral infection in 1 80% of LRTI patients (approximately 30% of these patients had evidence of simultaneous infections) compared with approximately 20% of healthy control subjects who had serological evidence of viral infection, and for whom no instances of multiple viruses were documented. Adenovirus and respiratory syncytial virus were more commonly associated with community-acquired pneumonia than other forms of LRTI. Furthermore, 14/15 (93%) of LRTI patients with documented bacterial infection also had serological evidence of viral infection, consistent with the paradigm that acute viral infections can predispose to secondary bacterial infections of the respiratory tract. The great Nobel laureate, Sir Peter Medawar (1915– 1987), defined a virus as ‘a piece of bad news wrapped up in protein’. Although viruses are well recognized as causes of human lower respiratory tract infections (LRTI), determining the pathogenic role of individual viruses for a given patient is challenging, in part because the various laboratory methods used to document specific viruses in clinical specimens have considerable technical limitations that can affect the interpretation of results. No perfect ‘gold standard’ for laboratory viral diagnosis exists, and while this may not have mattered so much in the past, when so few treatment options were available for respiratory viral infections, we are now living in an era in which novel antiviral interventions are rapidly making their way toward being implemented into practice and the accurate documentation of viral infections in various patient settings is becoming increasingly important. There are 2 main conceptual approaches to laboratory viral diagnosis: (1) testing for direct evidence of virus in clinical specimens from the site of infection, e.g. culture for replicating virus, electron microscopy for assembled virus, immunostaining for viral antigens, or molecular biology-based methods to detect viral nucleic acid; (2) testing for evidence of a host response to virus, in which serology, which measures the production of host antibody against virus in peripheral blood, is arguably the best-known and most commonly used technique. In this Published online: August 20, 2010