Role of 'atypical pathogens' among adult hospitalized patients with community-acquired pneumonia

Respirology. 2009 Nov;14(8):1098-105. doi: 10.1111/j.1440-1843.2009.01637.x. Epub 2009 Oct 5.

Abstract

Background and objective: Agents such as Mycoplasma pneumoniae, Chlamydophila pneumoniae and Legionella pneumophila are recognized as important causes of community-acquired pneumonia (CAP) worldwide. This study examined the role of these 'atypical pathogens' (AP) among adult hospitalized patients with CAP.

Methods: A prospective, observational study of consecutive adult CAP (clinico-radiological diagnosis) patients hospitalized during 2004-2005 was conducted. Causal organisms were determined using cultures, antigen testing and paired serology. Clinical/laboratory/radiological variables and outcomes were compared between different aetiologies, and a clinical prediction rule for AP was constructed.

Results: There were 1193 patients studied (mean age 70.8 +/- 18.0 years, men 59.3%). Causal organisms were identified in 468 (39.2%) patients: 'bacterial' (48.7%), 'viral' (26.9%), 'AP' (28.6%). The AP infections comprised Mycoplasma or Chlamydophila pneumoniae (97.8%) and co-infection with bacteria/virus (30.6%). The majority of AP infections involved elderly patients (63.4%) with comorbidities (41.8%), and more than one-third of patients were classified as 'intermediate' or 'high' risk CAP on presentation (pneumonia severity index IV-V (35.1%); CURB-65 2-5 (42.5%)). Patients with AP infections had disease severities and outcomes similar to patients with CAP due to other organisms (oxygen therapy 29.1% vs 29.8%; non-invasive ventilation 3.7% vs 3.3%; admission to the intensive care unit 4.5% vs 2.7%; length of hospitalization 6 day vs 7 day; 30-day mortality: 2.2% vs 6.0%; overall P > 0.05). Age <65 years, female gender, fever > or =38.0 degrees C, respiratory rate <25/min, pulse rate <100/min, serum sodium >130 mmol/L, leucocyte count <11 x 10(9)/L and Hb < 11 g/dL were features associated with AP infection, but the derived prediction rule failed to reliably discriminate CAP caused by AP from bacterial CAP (area under the curve 0.75).

Conclusions: M. pneumoniae and C. pneumoniae as single/co-pathogens are important causes of severe pneumonia among older adults. No reliable clinical indicators exist, so empirical antibiotic coverage for hospitalized CAP patients may need to be considered.

MeSH terms

  • Aged
  • Aged, 80 and over
  • Anti-Bacterial Agents / therapeutic use
  • Chlamydophila Infections / diagnosis
  • Chlamydophila Infections / epidemiology
  • Chlamydophila Infections / microbiology*
  • Chlamydophila pneumoniae / pathogenicity*
  • Community-Acquired Infections / diagnosis
  • Community-Acquired Infections / epidemiology
  • Community-Acquired Infections / microbiology*
  • Female
  • Hong Kong / epidemiology
  • Humans
  • Male
  • Middle Aged
  • Mycoplasma pneumoniae / pathogenicity*
  • Pneumonia, Bacterial / diagnosis
  • Pneumonia, Bacterial / epidemiology
  • Pneumonia, Bacterial / microbiology*
  • Pneumonia, Mycoplasma / diagnosis
  • Pneumonia, Mycoplasma / epidemiology
  • Pneumonia, Mycoplasma / microbiology*
  • Prevalence
  • Prognosis
  • Prospective Studies
  • Retrospective Studies
  • Severity of Illness Index

Substances

  • Anti-Bacterial Agents