The role of respiratory viruses in the etiology of bacterial pneumonia: An ecological perspective

Abstract

Pneumonia is the leading cause of death among children less than 5 years old worldwide. A wide range of viral, bacterial and fungal agents can cause pneumonia: although viruses are the most common etiologic agent, the severity of clinical symptoms associated with bacterial pneumonia and increasing antibiotic resistance makes bacterial pneumonia a major public health concern. Bacterial pneumonia can follow upper respiratory viral infection and complicate lower respiratory viral infection. Secondary bacterial pneumonia is a major cause of influenza-related deaths. In this review, we evaluate the following hypotheses: (i) respiratory viruses influence the etiology of pneumonia by altering bacterial community structure in the upper respiratory tract (URT) and (ii) respiratory viruses promote or inhibit colonization of the lower respiratory tract (LRT) by certain bacterial species residing in the URT. We conducted a systematic review of the literature to examine temporal associations between respiratory viruses and bacteria and a targeted review to identify potential mechanisms of interactions. We conclude that viruses both alter the bacterial community in the URT and promote bacterial colonization of the LRT. However, it is uncertain whether changes in the URT bacterial community play a substantial role in pneumonia etiology. The exception is Streptococcus pneumoniae where a strong link between viral co-infection, increased carriage and pneumococcal pneumonia has been established.

Keywords: Streptococcus pneumoniae; co-infection; ecology; influenza; pneumonia.

Figure 1.

Rate of hospitalization for pneumonia; the USA, 2007–2009. Adapted from Griffin et al. [48]

Figure 2.

Network of interactions between virus and bacteria in the upper respiratory tract. Figure 1A in van den Bergh et al. [26] used under the Creative Commons Attribution License. Green lines indicate synergistic associations and red lines indicate antagonistic associations. Solid lines indicate associations with P < 0.01 and dashed lines indicate associations with P between 0.01 and 0.05 for associations between species. enterovirus (EV), H. influenzae (HI), human adenovirus human (HAdV), bocavirus (HBoV), human coronavirus (HCov), human parechovirus (HPeV), human rhinovirus (HRV), influenza virus (IV), M. catarrhalis (MC), S. aureus (SA), S. pneumoniae (SP) and WU polyomavirus (WUPyV)