Introduction: Halm's clinical stability criteria have long guided antibiotic treatment and hospital discharge decisions for patients hospitalised with community-acquired pneumonia (CAP). Originally introduced in 1998, these criteria were established based on a relatively small and select patient population. Consequently, our study aims to reassess their applicability in management of CAP in a contemporary real-world setting.

Methods: This cohort study included 2918 immunocompetent patients hospitalised with CAP from three hospitals in Denmark between 2017-2020. The primary outcome was time to achieve clinical stability as defined by Halm's criteria. Additionally, we examined recurrence of clinical instability and severe complications. Cumulative incidence function or Kaplan-Meier survival curves were used to analyse these outcomes, considering competing risks.

Findings: The study population primarily comprised elderly individuals (median age: 75 years) with significant comorbidities. The median time to clinical stability according to Halm's criteria was 4 days, with one-fifth experiencing recurrence of instability after early clinical response (stability within 3 days). Severe complications within 30 days mainly comprised mortality, with rates of 5.1% (64/1257) overall in those with early clinical response, 1.7% (18/1045) in the subgroup without do-not-resuscitate orders, and 17.3% (276/1595) among the rest.

Interpretation: Halm's clinical stability criteria effectively classify CAP patients with different disease courses, yet achieving stability required more time in this aging population with substantial comorbidities and more severe disease. Early clinical response indicates reduced risk of complications, especially in those without do-not-resuscitate orders.