Community-acquired pneumonia distinguished from influenza infection based on clinical signs and symptoms during a novel (swine) influenza A/H1N1 pandemic

Prim Care Respir J. 2011 Dec;20(4):421-6. doi: 10.4104/pcrj.2011.00067.


Aims: The numbers of patients with influenza-like illnesses increase during influenza outbreaks. A study was undertaken to distinguish community-acquired pneumonia (CAP) from influenza based on clinical signs and symptoms.

Methods: This retrospective study investigated patients with positive results in the rapid influenza antigen test and those diagnosed with CAP during an influenza A/H1N1 pandemic. Significant factors for predicting risk for CAP within 48 hrs from onset and at diagnosis were selected by multiple regression analysis.

Results: Within 48 hrs of onset and at diagnosis, age and coarse crackles significantly increased the risk of CAP whereas sick contact, sore throat, and rhinorrhoea significantly decreased the risk of CAP. Duration of illness, sputum, dyspnoea, chest pain, and coarse crackles also significantly increased the risk of CAP at diagnosis.

Conclusions: CAP differed somewhat from influenza even within 48 hrs of onset and the differences became even more evident thereafter.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Antigens, Viral / blood
  • Community-Acquired Infections / diagnosis
  • Diagnosis, Differential
  • Female
  • Humans
  • Influenza A Virus, H1N1 Subtype* / immunology
  • Influenza, Human / diagnosis*
  • Influenza, Human / epidemiology*
  • Japan / epidemiology
  • Male
  • Middle Aged
  • Pandemics
  • Pneumonia / diagnosis*
  • Pneumonia / epidemiology*
  • Pneumonia / microbiology
  • Regression Analysis
  • Retrospective Studies
  • Sputum / microbiology
  • Young Adult


  • Antigens, Viral