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Correspondence |

Flawed Comparative Groups Lead to Flawed Conclusions FREE TO VIEW

Peter Collignon, MB, BS
Author and Funding Information

Affiliations: Dr. Collignon is affiliated with the Australian National University.

Correspondence to: Peter Collignon, MB, BS, Canberra Hospital, PO Box 11, Woden, ACT 2607, Australia; e-mail: collignon@webone.com.au


Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/site/misc/reprints.xhtml).


© 2009 American College of Chest Physicians


Chest. 2009;136(4):1184-1185. doi:10.1378/chest.09-1153
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In a recent issue of CHEST (May 2009), Winchester et al1 concluded that not prescribing antibiotics on the day of the diagnosis of lower respiratory tract infections (LRTIs) resulted in more deaths and hospital admissions.

Investigating large populations (as this team did) on whether limiting antibiotic use causes harm is very important. Unfortunately, because of flawed comparative groups and design, this study1 leaves the reader with false impressions and misleading conclusions. The authors imply that if public health messages strive to limit antibiotic use to curtail antibiotic resistance, this will cost lives. However, their data also show that patients receiving therapy with antibiotics in the 7 days prior to the diagnosis of an LRTI had a substantially increased death rate!

More deaths occurred in those patients not receiving antibiotics on the same day as the diagnosis of LRTI. However, the two comparative groups (antibiotics or no antibiotics) are not comparable. General practitioners withheld therapy with antibiotics disproportionately among very old patients and those patients with major morbidities (specifically, those patients > 80 years of age, and those patients with a malignancy, congestive heart failure, dementia, and hemiplegia). Thus, the very people who were most likely to have the worst outcomes were also more likely not to receive antibiotics. Thus, it is hardly surprising that the “no-antibiotic” group had worse outcomes.

If the very old and those with severe morbidities were excluded from both comparative groups, would there still be a difference in outcomes? I suspect not.

Another problem with the study design is that the definition of LRTIs included all cases of pneumonia, influenza, and acute bronchitis. Therapy with antibiotics is needed for the treatment of pneumonia. However, antibiotic use has few benefits in the treatment of patients with acute bronchitis2 or uncomplicated influenza. If this study were trying to look at the benefits of antibiotic therapy compared with harm, should not the latter two conditions be separated from pneumonia for analysis?

This study resulted from an idea put forward at a round table meeting sponsored by Abbott Laboratories.1 One hopes that the genesis of the idea did not in some way influence the way this study was reported, either in this article itself or in the material sent to the media. Already as a result of this study, we have the message being promulgated in general medical publications3,4 that the more judicious use of antibiotics is harmful. The misleading conclusions and impressions left by this article1 have unjustifiably been used to undermine a very important public health message on the overuse of antibiotics. I remain surprised that this article was ever published in its current form, given the obvious differences in the comparative groups and, thus, the inability to draw any meaningful conclusions.

Financial/nonfinancial disclosures: The author has reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Winchester CC, Macfarlane TV, Thomas M, et al. Antibiotic prescribing and outcomes of lower respiratory tract infection in UK primary care. Chest. 2009;135:1163-1172. [PubMed] [CrossRef]
 
Smith SM, Fahey T, Smucny J, et al. Antibiotics for acute bronchitis. Cochrane Database Syst Rev (database online). 2004;Issue 4
 
Woodward M. Antibiotics curbs may worsen LRTI outcomes: efforts to curb antibiotic use by GPs for lower respiratory tract infections may have gone too far, a new study suggests.Accessed September 7, 2009 Available at:http://www.6minutes.com.au/articles/z1/view.asp?id=480154.
 
Anekwe L. Dramatic benefits for early antibiotics in at-risk patients with LRTI: prescribing antibiotics on the day of diagnosis of a lower respiratory tract infection “dramatically reduces admissions and mortality related to respiratory infection, UK research reports.Accessed September 7, 2009 Available at:http://www.pulsetoday.co.uk/story.asp?sectioncode=23&storycode=4122518&c=2.
 

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References

Winchester CC, Macfarlane TV, Thomas M, et al. Antibiotic prescribing and outcomes of lower respiratory tract infection in UK primary care. Chest. 2009;135:1163-1172. [PubMed] [CrossRef]
 
Smith SM, Fahey T, Smucny J, et al. Antibiotics for acute bronchitis. Cochrane Database Syst Rev (database online). 2004;Issue 4
 
Woodward M. Antibiotics curbs may worsen LRTI outcomes: efforts to curb antibiotic use by GPs for lower respiratory tract infections may have gone too far, a new study suggests.Accessed September 7, 2009 Available at:http://www.6minutes.com.au/articles/z1/view.asp?id=480154.
 
Anekwe L. Dramatic benefits for early antibiotics in at-risk patients with LRTI: prescribing antibiotics on the day of diagnosis of a lower respiratory tract infection “dramatically reduces admissions and mortality related to respiratory infection, UK research reports.Accessed September 7, 2009 Available at:http://www.pulsetoday.co.uk/story.asp?sectioncode=23&storycode=4122518&c=2.
 
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