title: Role of 'atypical pathogens' among adult hospitalized patients with community-acquired pneumonia.
abstract: 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.
authors.affiliation: Department of Medicine and Therapeutics, Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, NT, Hong Kong.
authors.forename: Grace
authors.initials: G
authors.lastname: Lui
authors.forename: Margaret
authors.initials: M
authors.lastname: Ip
authors.forename: Nelson
authors.initials: N
authors.lastname: Lee
authors.forename: Timothy H
authors.initials: TH
authors.lastname: Rainer
authors.forename: Shin Y
authors.initials: SY
authors.lastname: Man
authors.forename: Clive S
authors.initials: CS
authors.lastname: Cockram
authors.forename: Gregory E
authors.initials: GE
authors.lastname: Antonio
authors.forename: Margaret H L
authors.initials: MH
authors.lastname: Ng
authors.forename: Michael H M
authors.initials: MH
authors.lastname: Chan
authors.forename: Shirley S L
authors.initials: SS
authors.lastname: Chau
authors.forename: Paulina
authors.initials: P
authors.lastname: Mak
authors.forename: Paul K S
authors.initials: PK
authors.lastname: Chan
authors.forename: Anil T
authors.initials: AT
authors.lastname: Ahuja
authors.forename: Joseph J Y
authors.initials: JJ
authors.lastname: Sung
authors.forename: David S C
authors.initials: DS
authors.lastname: Hui
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D023521:Chlamydophila Infections / Q000175:diagnosis / Q000453:epidemiology / Q000382:microbiology*; D016993:Chlamydophila pneumoniae / Q000472:pathogenicity*; D017714:Community-Acquired Infections / Q000175:diagnosis / Q000453:epidemiology / Q000382:microbiology*; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009177:Mycoplasma pneumoniae / Q000472:pathogenicity*; D018410:Pneumonia, Bacterial / Q000175:diagnosis / Q000453:epidemiology / Q000382:microbiology*; D011019:Pneumonia, Mycoplasma / Q000175:diagnosis / Q000453:epidemiology / Q000382:microbiology*; D015995:Prevalence; D011379:Prognosis; D011446:Prospective Studies; D012189:Retrospective Studies; D012720:Severity of Illness Index
chemical_list: D000900:Anti-Bacterial Agents