New ATS CAP Guidance Sparks First IDSA Split in Two Decades Over Empiric Antibiotics in Viral Pneumonia

Community-acquired pneumonia (搜索)搜索该疾病 (CAP) remains one of the most common reasons adults are admitted to the hospital in the U.S., accounting for more than 1.4 million emergency department visits, 740,000 hospitalizations, and 41,000 deaths annually. In July 2025, the American Thoracic Society (搜索)搜索该词条 (ATS) released a focused update to the comprehensive 2019 joint ATS and Infectious Diseases Society of America (搜索)搜索该词条 (IDSA) CAP guideline, updating guidance in four areas where new evidence has emerged since 2019: lung ultrasound as a diagnostic alternative to chest radiography, the management of CAP when respiratory viral testing is positive, shorter antibiotic duration in clinically stable patients, and the role of systemic corticosteroids (搜索)搜索该药品 in non-severe versus severe CAP.

The IDSA declined to co-endorse the final guideline, the first major divergence between the two societies on CAP guidance in more than two decades. The disagreement centers on a single recommendation: whether hospitalized patients with CAP and a positive respiratory viral test should routinely receive empiric antibiotics in the absence of any comparative supporting evidence.

Lung Ultrasound as a Diagnostic Alternative

For adults with suspected CAP, the 2025 ATS guideline endorses lung ultrasound (LUS) as an acceptable diagnostic alternative to chest radiography where appropriate clinical expertise exists. A meta-analysis of 11 studies using computed tomography as the reference standard found that LUS outperformed chest radiography on both sensitivity (95% versus 70%) and specificity (75% versus 55%), though evidence quality was rated low due to inconsistency across studies, yielding a conditional recommendation.

For hospitalists with point-of-care ultrasound (POCUS) training, LUS is appropriate when chest radiography is unavailable or when computed tomography carries undue risk. The guideline defines adequate expertise as formal credentialing, standardized imaging protocols, and image archiving equivalent to radiology reporting standards. LUS is not endorsed for routine substitution for chest radiography without institutional credentialing pathways. Obesity, wounds, scars, and drains may limit accuracy, and LUS cannot evaluate alternative diagnoses such as pulmonary embolism or malignancy.

Empiric Antibacterial Therapy When a Respiratory Virus Is Detected

For adult outpatients without comorbidities, the guideline suggests withholding empiric antibiotics when a respiratory virus is detected, given the low risk of serious outcomes if treatment is deferred and the established harms of unnecessary antibiotic exposure. For outpatients with comorbidities, empiric antibiotics are suggested given the higher risk of serious outcomes from untreated bacterial co-infection. For adult inpatients with non-severe CAP and a positive respiratory virus test, the guideline suggests empiric antibiotics. For inpatients with severe CAP, empiric antibiotics are suggested regardless of viral detection. All four recommendations are conditional, based on very low-quality evidence.

The evidentiary problem is straightforward: the committee identified no comparative studies for the antibiotic versus no antibiotic question in viral CAP, yet issued a treat-by-default recommendation for inpatients, relying on expert consensus rather than comparative data. IDSA declined to co-endorse the guideline specifically on this point, and four IDSA members published a formal dissent in December 2025. Their core argument was that adverse events occur in up to one-quarter of hospitalized patients receiving antibiotics, and that treating viral-positive non-severe inpatients empirically conflicts with established antimicrobial stewardship principles.

In the absence of comparative evidence, the decision falls to clinical judgment. Normal inflammatory markers and a patchy bilateral infiltrate pattern favor withholding antibiotics. Purulent sputum, lobar consolidation, rising C-reactive protein (搜索)搜索该靶点, high illness severity, or significant comorbidities favor treatment.

Antibiotic Duration for CAP

For adult inpatients with non-severe CAP who reach clinical stability, the guideline now suggests fewer than five days of antibiotics, with a minimum of three days, rather than the five-or-more-day standard from the 2019 guidance. This is a conditional recommendation supported by low-quality evidence. For inpatients with severe CAP reaching clinical stability, five or more days remains the standard, a strong recommendation, though the underlying evidence remains low quality.

Clinical stability is defined as afebrile, heart rate less than 100 beats per minute, respiratory rate less than 24 breaths per minute, systolic blood pressure of 90 mmHg or greater, oxygen saturation of 90% or greater on room air or at baseline oxygen requirement, and normal mentation.

The key supporting trial is the PTC trial, a double-blind randomized controlled trial demonstrating non-inferiority of discontinuing beta-lactam (搜索)搜索该药品 treatment after three days compared to eight-day treatment in non-critically ill hospitalized CAP patients.

Where the 2019 guideline set five days as a minimum, this update brings that minimum down to three days for stable non-severe patients. The onus shifts to justifying continuation, not discontinuation. Exceptions include Staphylococcus aureus, Pseudomonas aeruginosa, Legionella pneumophila, and other intracellular microorganisms, and complications including empyema, abscess, bacteremia, extrapulmonary infection, or structural lung disease. Shorter treatment courses also reduce adverse drug events, Clostridioides difficile risk, and the selective pressure that drives antimicrobial resistance.

Systemic Corticosteroids for Hospitalized CAP

Systemic corticosteroids (搜索)搜索该药品 are not recommended in non-severe CAP, a strong recommendation despite low-quality evidence, anchored in the risk of harm (primarily hyperglycemia) in patients for whom the evidence shows no benefit. In severe CAP, corticosteroids are conditionally suggested, except in patients with influenza-associated pneumonia, where observational data suggest corticosteroids may worsen outcomes.

The IDSA-ATS severity criteria define severe CAP as the presence of one major criterion (need for mechanical ventilation or vasopressors) or three or more minor criteria, including tachypnea, hypoxemia, multilobar disease, encephalopathy, uremia, leukopenia, thrombocytopenia, hypothermia, and hypotension requiring aggressive fluid resuscitation. Corticosteroids (搜索)搜索该药品 are most appropriate when initiated within 24 hours of meeting severity criteria and when inflammatory markers are elevated, particularly C-reactive protein (搜索)搜索该靶点, which has been identified as a predictor of corticosteroid benefit in an individual patient data meta-analysis of eight randomized trials. Other factors favoring corticosteroid use include both intensive care unit admission and respiratory failure with a PaO2/FiO2 ratio below 300.

Pneumonia Severity Index and CURB-65 (confusion, urea, respiratory rate, blood pressure and age at least 65) scores were not designed to determine intensive care unit treatment and do not define severe CAP for purposes of this guideline. Severity classification determines corticosteroid eligibility, antibiotic duration, and the extent of microbiologic evaluation.

The Inter-Society Disagreement

The guideline was developed by a multidisciplinary panel of 18 experts representing pulmonology, infectious disease, internal medicine, critical care, hospital medicine, emergency medicine, and evidence synthesis. Systematic reviews were conducted from January 1946 through March 2023, with updates in November 2024 and February 2025, applying the Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology.

The formal IDSA dissent, published in December 2025 by four IDSA committee members, gives credit to the shortened antibiotic duration recommendations as a meaningful contribution, but questions both the evidence and the process behind the viral-positive antibiotic recommendation.

GRADE has no established framework for rating noncomparative evidence, and the dissent argues that issuing a recommendation without that foundation was hard to defend. The dissent raises three concerns about how the process unfolded. The critical vote took place at a hybrid meeting at the ATS annual International Conference in Washington, D.C. in May 2023, where most ATS representatives attended in person, and most IDSA representatives joined remotely, creating unequal conditions for in-person and remote participants. The nonvoting methodologists were drawn predominantly from the ATS guideline methodology training program, with the lead methodologist also representing ATS. The third concern: without trial data, the committee lacked a structured approach for evaluating the observational evidence it relied on instead.

The dissent makes clear that the concern is not procedural alone: the committee recommended routine antibiotic treatment in the absence of any supporting comparative evidence, in a clinical context where antibiotic harms are well established. Notably, all 15 independent peer reviewers voiced concern about this recommendation, yet the committee opted to maintain it. The guideline was not approved by the IDSA, the first time in over two decades that the two societies have parted ways on CAP management. Resolving this disagreement will require a randomized trial of antibiotics versus no antibiotics in hospitalized patients with confirmed viral pneumonia.