How well does procalcitonin distinguish bacterial from viral causes of community-acquired pneumonia in hospitalized patients?

Not extremely well! Although a recent multicenter prospective study in adult hospitalized patients reported that the median procalcitonin (PCT) concentration was significantly lower for community-acquired pneumonia (CAP) caused by viral compared to bacterial pathogens, normal PCT values at  <0.1 ug/ml and <0.25 ug/ml  were also found in 12.4% and 23.1% of typical bacterial cases, respectively1

This means that we could potentially miss about a quarter of CAP cases due to typical bacterial causes if we use the <0.25 ug/ml threshold (<0.20 is ug/ml has often  been used to exclude sepsis2). Based on the results of these and another study3, no threshold for PCT can reliably distinguish bacterial from viral etiologies of CAP.4  Clinical context is essential in interpreting PCT levels!

Can PCT distinguish Legionella from other atypical bacterial causes of CAP (eg, caused by Mycoplasma or Chlamydophila)? The answer is “maybe”! Legionella was associated with higher PCT levels compared to  Mycoplasma and Chlamydophila in one study1, but not in another3

For a related pearl on P4P go to https://pearls4peers.com/2017/07/01/should-i-order-serum-procalcitonin-on-my-patient-with-suspected-infection   

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References

  1. Self WH, Balk RA, Grijalva CG, et al. Procalcitonin as a marker of etiology in adults hospitalized with community-acquired pneumonia. Clin Infect Dis 2017;65:183-90. https://www.ncbi.nlm.nih.gov/pubmed/28407054
  2. Meisner M. Update on procalcitonin measurements. Ann Lab Med 2014;34:263-73.
  3. Krüger S, Ewig S, Papassotiriou J, et al. Inflammatory parameters predict etiologic patterns but do not allow for individual prediction of etiology in patients with CAP-Results from the German competence network CAPNETZ. Resp Res 2009;10:65. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2714042/pdf/1465-9921-10-65.pdf
  4. Bergin SP, Tsalik EL. Procalcitonin: the right answer but to which question? Clin Infect Dis 2017; 65:191-93. https://academic.oup.com/cid/article-abstract/65/2/191/3605416/Procalcitonin-The-Right-Answer-but-to-Which?redirectedFrom=fulltext
How well does procalcitonin distinguish bacterial from viral causes of community-acquired pneumonia in hospitalized patients?

In hospitalized patients with community-acquired pneumonia (CAP), has empiric treatment with beta-lactam plus macrolide or a quinolone been shown to be superior to beta-lactam monotherapy ?

Actually no!

In fact, a 2015 study of CAP from Netherlands, published in New England Journal of Medicine, demonstrated that empiric treatment with beta-lactam monotherapy was not inferior to strategies using a beta-lactam-macrolide combination or fluoroquinolone monotherapy with regard to 90-day mortality, or length of hospital stay (1). To help exclude Legionella pneumonia (often accounting for <5% of CAP[2]), urine Legionella antigen was routinely performed in this study.

So once Legionella has been reasonably excluded, unless suspicion for other atypical causes of CAP (i.e. Mycoplasma pneumoniae or Chlamydophila pneumoniae) remains high, empiric monotherapy with a beta-lactam (e.g. ceftriaxone) may be just as effective in many cases of CAP.

References

1. Postma DF1, van Werkhoven CH, van Elden LJ, et al. CAP-START Study Group Antibiotic treatment strategies for community-acquired pneumonia in adults. N Engl J Med. 2015;372:1312-23.  https://www.ncbi.nlm.nih.gov/pubmed/25830421  

2. von Baum H, Ewig S, Marre R, et al. Competence Network for Community Acquired Pneumonia Study Group. Community-acquired Legionella pneumonia: new insights from the German competence network for community acquired pneumonia. Clin Infect Dis 2008;46:1356. https://www.ncbi.nlm.nih.gov/pubmed/18419436

Contributed by Jessica A. Hennessey, MD, PhD, Mass General Hospital, Boston, MA

In hospitalized patients with community-acquired pneumonia (CAP), has empiric treatment with beta-lactam plus macrolide or a quinolone been shown to be superior to beta-lactam monotherapy ?