Compared to 2007,1 the 2019 ATS/IDSA guidelines2 have 2 major “Do’s” and 2 major “Dont’s” in the diagnostic approach to CAP in hospitalized patients:
- DO order sputum and blood cultures in patients empirically treated for methicillin-resistant Staphylococcus aureus (MRSA) or Pseudomonas aeruginosa—in addition to those with severe CAP as in 2007.
- DO order rapid influenza molecular assay—in preference to antigen test— when influenza viruses are circulating in community, irrespective of pneumonia severity
- DON’T routinely order urine antigens for pneumococcal or Legionella antigens, except in severe CAP or in the presence of suggestive epidemiological factors (eg. Legionella outbreak, recent travel)
- DON’t routinely order serum procalcitonin to determine need for initial antibacterial therapy
Patients at risk of MRSA or P. aeruginosa include those with prior infection with the same pathogens as well as those with hospitalization and treated with parenteral antibiotics—in or out of the hospital— in the last 90 days; HCAP is no longer recognized as an entity.
The definition of severe CAP is unchanged: 1 of 2 major criteria (septic shock or respiratory failure requiring mechanical ventilation) or 3 or more of the following minor criteria or findings listed below:
- Respiratory rate ≥30 breath/min
- Hypotension requiring aggressive fluid resuscitation
- Hypothermia (core temperature <36 ᵒC, 96.8 ᵒF)
- Multilobar infiltrates
- Leukopenia (WBC <4,000/ul)
- Thrombocytopenia (platelets <100,000/ul)
- BUN ≥20 mg/dl
- Pa02/FI02 ratio ≤250
Keep in mind that these guidelines focus on adults who are not immunocompromised or had recent foreign travel and are often based on expert opinion but low or very low quality evidence due to the dearth of properly designed studies.2
Bonus Pearl: Did you know that the urine Legionella antigen only tests for L. pneumophila type I, with an overall sensitivity ranging from 45% to 100%!3,4
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- Mandell LA, Wunderink RG, Anzueto A. Infectious Disease Society of America/American Thoracic Society Consensus Guidelines on the Management guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis 2007;44:S27-72. https://www.ncbi.nlm.nih.gov/pubmed/17278083
- Metlay JP, Waterer GW, Long AC, et al. Diagnosis and treatment of adults with community-acquired pneumonia. Am J Respir Crit Care Med 2019;200:e45-e67. https://www.ncbi.nlm.nih.gov/pubmed/31573350
- Blazquez RM, Espinosa FJ, Martinez-Toldos CM, et al. Sensitivity of urinary antigen test in relation to clinical severity in a large outbreak of Legionella pneumonia in Spain. Eur J Clin Microbiol Infect Dis 2005;24:488-91. https://www.ncbi.nlm.nih.gov/pubmed/15997369
- Marlow E, Whelan C. Legionella pneumonia and use of the Legionella urinary antigen test. J Hosp Med 2009;4:E1-E2. https://www.ncbi.nlm.nih.gov/pubmed/19301376