Skip Navigation

Community-Acquired Pneumonia: A Viral Storm

Amesh A. Adalja, MD, FACP, FACEP, July 31, 2015

Community-acquired pneumonia is a very common condition, and physicians of all specialties have experience with it. Even in the modern era, it still ranks high among causes of death. Most community-acquired pneumonia cases have been considered to be caused almost exclusively by bacteria, and prompt antibiotic therapy is considered a major quality measure. As such, community-acquired pneumonia is a major driver of overall antibiotic consumption.

In many cases, a specific pathogen-level diagnosis is not made, and treatment is largely empiric. However, the EPIC study, published recently in the New England Journal of Medicine, attempts to provide pathogen-level diagnosis to more fully understand the etiology of this common condition.


Viruses > Bacteria

In EPIC, Jain and colleagues studied hospitalized patients with community-acquired pneumonia in 5 hospitals in Chicago and Nashville. More than 2,000 patients were enrolled, and the etiologic agent was pursued using myriad means, including culture, antigen testing, serology, and molecular diagnostics. Important characteristics of those studied included:

  • A median age of 57 years
  • ICU admission in 21% of cases
  • A 2% mortality rate

The most striking finding was that a pathogen was identified in just 38% of patients and that viruses were found more than twice as often as bacteria (23% vs. 11%). Rhinovirus was the most common microbe found, with influenza and pneumococcus ranking 2nd and 3rd. Both a viral and a bacterial cause were noted in 3% of cases.


Opportunity for Antimicrobial Stewardship

This article has several implications, one of which is that, despite aggressive searching for pathogens, 62% of patients were left without a diagnosis for their pneumonia. The inability to find an agent in the majority of pneumonia cases argues that diagnostic testing has much room for improvement.

Another finding is that viruses—not bacteria—accounted for a major portion of the identified pathogens. Since antibiotics are not indicated for viral infections, this presents a major opportunity for stewardship in the use of antibiotics by encouraging more widespread and routine use of respiratory virus testing, followed by de-escalation of antibiotic therapy when a virus is identified. Such an approach can be coupled with the use of procalcitonin, a highly specific marker for bacterial infection, to further refine management.

The EPIC study is a major contribution to our understanding of a very common condition, and its findings should inform practice patterns and guideline development.



Jain S, Self WH, Wunderink RG, et al. Community-acquired pneumonia requiring hospitalization among U.S. adults. N Engl J Med 2015;373:415-427.