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Levels of evidence supporting European and American community-acquired pneumonia guidelines


Optimal clinical decisions should be supported by clinical practice guidelines (CPG) based on evidence generated from randomized clinical trials (RCT). We aimed to evaluate the class and level of evidence (LOE) supporting the international community-acquired pneumonia (CAP) guidelines and their variation over time. The 2019 Infectious Diseases Society of America/American Thoracic Society (IDSA/ATS) and the 2011 European Respiratory Society/European Society Clinical Microbiology Infectious Diseases (ERS/ESCMID) CPG and its immediate predecessors (2007 and 2005) were evaluated. The number of recommendations and distribution as LOE A (supported by multiple RCT or a single, large RCT), B (supported by data from a single RCT or observational studies) and C (expert opinion, case studies, or standard of care) was identified. Overall, recommendations for diagnosis, management, and prevention were graded as strong in 51.4%, 62.9%, and 23.5% in spite that they were supported by LOE A in 5.7%, 11.1%, and 52.9%, respectively. In the 2019 ATS/IDSA guidelines (39 recommendations), 7.7% (n = 3) recommendations were classified as LOE A, 30.8% (n = 12) as LOE B, and 61.5% (24%) as LOE C. Across the 2011 ERS/ESCMID guidelines (68 recommendations), 21.2% (n = 14) recommendations were classified as LOE A, 4.6% (n = 3) as LOE B, and 74.2% (n = 49) as LOE C. When comparing with prior versions, the proportion of recommendations that were LOE A did not significantly increase in ERS/ESCMID (21.2% vs 20%) and decreased in ATS/IDSA (7.7% vs 32.0%). In conclusion, large randomized trials or network meta-analysis including comparison of regimens to identify high probability of best cure and mortality is an unmet clinical need on CAP.

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American Thoracic Society


Acute respiratory distress syndrome


Community acquired pneumonia


Chronic obstructive pulmonary disease


Clinical practice guidelines


European Respiratory Society


European Society of Clinical Microbiology and Infectious Diseases


Infectious Diseases Society of America


Level of evidence


Network meta-analysis




Randomized controlled trial


Systematic review


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Authors appreciate comments from Maria Teresa Martin, Microbiology Department, Vall d’Hebron University Hospital who helped to improve the final manuscript.


This work was funded in part by CIBERES, Instituto Salud Carlos III, Madrid, Spain (Fondos FEDER) (CB06–06-036).

Author information

JR and JFC designed the study. The recommendations were abstracted by a single reviewer (JFC) and validated by two other reviewers (LC and STM). JFC analyzed data and write the first manuscript draft. All authors approved the final version of the manuscript. JFC takes full responsibility for the integrity of the reported data.

Correspondence to João Ferreira-Coimbra.

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Competing interests

Dr. Rello has served as consultant and in the speakers’ bureau for Nzbriva, MSD, Pfizer & Astellas. The remaining authors have no conflicts of interest to declare.

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Ferreira-Coimbra, J., Tejada, S., Campogiani, L. et al. Levels of evidence supporting European and American community-acquired pneumonia guidelines. Eur J Clin Microbiol Infect Dis (2020).

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  • Community-acquired pneumonia
  • Diagnosis
  • Therapy
  • Prevention
  • Randomized controlled trial
  • Evidence-based medicine