Severe Community-Acquired Pneumonia: A 2025 Not-IDSA Guideline

A thoracic society and the IDSA stay on their separate paths

Since 2005, the major professional society for infectious diseases (IDSA) periodically issued joint guidance documents with a major US critical care society on the prevention, diagnosis, and treatment of community-acquired and hospital-acquired pneumonia.

Their co-authorship increased the credibility and authority of their guidance, most recently in 2019.

But it turns out they were never married, only dating.

In 2021, ATS issued its own interim guideline update on nucleic acid testing for suspected pneumonia, without IDSA’s official endorsement.

In July 2025, ATS published another update on the diagnosis and treatment of pneumonia, again without IDSA’s endorsement, although nine authors from IDSA were on the initial panel and some or all are listed as co-authors.

The 119-page guideline document offers advice stratified by severity of community-acquired pneumonia. This analysis will focus on the guidelines for immunocompetent patients admitted to the hospital with severe CAP not due to SARS-CoV-2.

PulmCCM is not affiliated with ATS, IDSA, or any other professional society.

Guidelines Are Not Gospel

The authors wisely reminded all stakeholders that guidelines are merely a starting point, always superseded by sound clinical judgment focused on individualized, patient-centered decision-making:

The majority of the recommendations in this guideline update are conditional, meaning that a sizable minority of patients may not want the suggested course of action, and clinicians must help patient [sic] arrive at a management decision consistent [sic] their values and preferences. Clinicians should review [factors relevant to their patient] and individualize recommendations based upon their assessment of how well the guidelines apply to their patient. … No one responsible for evaluating clinicians’ actions should attempt to apply the recommendations from these guidelines by rote or in a blanket fashion.

Definition of Severe CAP

For the purposes of the panel’s recommendations, severe community-acquired pneumonia was defined as CAP requiring mechanical ventilation or vasopressors, or with three “minor criteria” (e.g., tachypnea >30 breaths/minute, P/F ratio <250, or various “SIRS/sepsis” criteria.

Which Antibiotics to Prescribe?

Antibiotic selection for severe community-acquired pneumonia was not covered in this interim guideline update.

That leaves us to refer to the 2019 IDSA/critical care joint guideline, which recommended a beta-lactam (e.g., ampicillin/sulbactam 1.5 to 3 g q. 6 hours, cefotaxime 1-2 g q. 8 hours, ceftriaxone 1-2 g daily, or ceftaroline 600 mg q. 12 hours) plus either a macrolide (azithromycin 500 mg daily or clarithromycin 500 mg twice daily) or a fluoroquinolone with respiratory penetration (levofloxacin 750 mg daily or moxifloxacin 400 mg daily).

Initial MRSA coverage with vancomycin (15 mg/kg every 12 hours, adjusted based on levels) or linezolid (600 mg every 12 hours) should be added for patients with prior respiratory isolation of MRSA (including nasal swab PCR), or who have a recent hospitalization with I.V. antibiotics and locally validated risk factors for MRSA.

Pseudomonas coverage with cefepime (2 g every 8 hours), piperacillin-tazobactam (4.5 g every 6 hours), ceftazidime (2 g every 8 hours), meropenem (1 g every 8 hours), imipenem (500 mg every 6 hours), or aztreonam (2 g every 8 hours) should be provided for patients with recent hospitalizations with I.V. antibiotics and locally validated risk factors for Pseudomonas.

“Locally validated risk factors” for resistant pathogens might include ESRD on dialysis (for MRSA), tracheostomy in situ (for Pseudomonas) or nursing home residence (for Pseudomonas or MRSA), among many others, but the idea is that individual hospital infection control departments would create advisements to clinicians based on observed local patterns of resistance.

Antibiotic Duration in Severe Community-Acquired Pneumonia