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Predicting Community-Acquired Pneumonia EtiologyPredicting Community-Acquired Pneumonia Etiology FREE TO VIEW

Douwe F. Postma, MD; Cornelis H. van Werkhoven, MD; Jan Jelrik Oosterheert, MD, PhD; Marc J. M. Bonten, MD, PhD
Author and Funding Information

From the Julius Center for Health Sciences (Drs Postma, van Werkhoven, and Bonten), the Department of Internal Medicine and Infectious Diseases (Dr Oosterheert), and the Department of Medical Microbiology (Dr Bonten), University Medical Center Utrecht.

Correspondence to: Douwe F. Postma, MD, University Medical Center Utrecht, Julius Center for Health Sciences, PO Box 85500, 3508 GA Utrecht, The Netherlands; e-mail: d.f.postma@umcutrecht.nl


Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2013;144(6):1975-1976. doi:10.1378/chest.13-1756
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To the Editor:

We read with interest the recent study by Cillóniz et al1 in CHEST (September 2013), in which several associations between the cause and outcome of community-acquired pneumonia (CAP) were reported in patients > 65 years of age, studied over a period of 12 years. The authors mention that the nonhomogeneous assessment of microbial cause is a potential limitation. In our opinion, this is an understatement of the bias that may have resulted from this approach, and this limitation precludes the conclusion that was reached.

The most important finding of the study was that the presence of comorbidities was associated more with potential multidrug-resistant (MDR) pathogens as a cause of CAP than was age. Thus, the authors concluded that “comorbidities rather than age should be considered in the selection of antibiotic treatment.” However, the outcome (in this case, a microbial cause) was not assessed uniformly in all included patients, which is a well-known cause of bias in predictive research.2 Apparently, microbial testing was left to the discretion of the treating physician. This is at least suggested by the pattern of microbial testing: serologic tests in 1,537 patients (44%), sputum cultures in 1,913 patients (54%), and blood cultures in 2,753 patients (78%).3 By ignoring the fact that microbial tests could be different across patients, the authors implicitly assumed that the tests were missing at random. However, in clinical practice, the choice for microbial testing is often influenced by patient and disease characteristics. Therefore, more extensive diagnostic testing in patients with comorbidities may well explain the higher prevalence of potential MDR pathogens in this patient group. Demonstration of comparable diagnostic procedures in patients with and without comorbidities would reduce the likelihood of bias, although even that would not rule out bias completely. It is hardly possible to adjust for this analytically, even when information on why certain microbial tests were (or were not) obtained was available.

Because of global aging and the corresponding increase in the number of comorbidities, which will also occur in patients with CAP, a recommendation to include MDR antibiotic coverage based on comorbidities inevitably increases antibiotic use. In an era of increasing antimicrobial resistance and a high prevalence of nosocomial Clostridium difficile infection, such recommendations should be based on unbiased results. Because the cause of CAP cannot be reliably determined by clinical data, empirical antibiotic therapy should be guided by local epidemiologic data, the site of admission, and prior microbial culture results, rather than by the presence of comorbidities.

References

Cillóniz C, Polverino E, Ewig S, et al. Impact of age and comorbidity on etiology and outcome in community-acquired pneumonia. Chest. 2013;144(3):999-1007. [CrossRef] [PubMed]
 
Moons KG, Royston P, Vergouwe Y, Grobbee DE, Altman DG. Prognosis and prognostic research: what, why, and how? BMJ. 2009;338:b375. [CrossRef] [PubMed]
 
Cillóniz C, Ewig S, Polverino E, et al. Microbial aetiology of community-acquired pneumonia and its relation to severity. Thorax. 2011;66(4):340-346. [CrossRef] [PubMed]
 

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References

Cillóniz C, Polverino E, Ewig S, et al. Impact of age and comorbidity on etiology and outcome in community-acquired pneumonia. Chest. 2013;144(3):999-1007. [CrossRef] [PubMed]
 
Moons KG, Royston P, Vergouwe Y, Grobbee DE, Altman DG. Prognosis and prognostic research: what, why, and how? BMJ. 2009;338:b375. [CrossRef] [PubMed]
 
Cillóniz C, Ewig S, Polverino E, et al. Microbial aetiology of community-acquired pneumonia and its relation to severity. Thorax. 2011;66(4):340-346. [CrossRef] [PubMed]
 
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