Severe community-acquired pneumonia (SCAP) is the most lethal form of community-acquired pneumonia (CAP), with mortality rates exceeding 30% in cases involving shock or mechanical ventilation. Usually, SCAP represents 5 to 10% of all hospitalized patients with CAP. A pragmatic definition of SCAP is to refer to those patients with CAP who are admitted to the intensive care unit (ICU). This definition is likely biased due to the significant variability of ICU resources in different countries. Another way to define SCAP is by using the 2007 minor Infectious Diseases Society of America (IDSA)/American Thoracic Society (ATS) criteria (3 out of 9 criteria) or major criteria (shock or need for mechanical ventilation). These criteria have been in use since 2007 in clinical practice and for research purposes.

In this issue of Seminars in Respiratory and Critical Care Medicine 2024, we have compiled 11 articles covering several critical issues in SCAP. The epidemiology of SCAP, including definitions, is summarized by Rodrigo Cavallazzi and colleagues from Julio Ramirez's group in Louisville. Microbial diagnosis of SCAP, an extremely important point, is covered by Pickens and colleagues from Rick Wunderink's group. This article includes a special mention of rapid molecular techniques, including available platforms that provide rapid diagnosis, which could potentially change the prognosis of the patients.

The use of noninvasive mechanical ventilation (NIMV) in SCAP to avoid intubation is a matter of debate concerning when, for how long, and which type of NIMV is better. The evidence, pitfalls, pros and cons, and recommendations about the use of NIMV in SCAP to avoid intubation are very nicely updated by Miquel Ferrer and Massimo Antonelli.

Empirical and targeted antibiotic administration is the cornerstone of SCAP treatment. Old drugs still form the backbone of SCAP antibiotic treatment, but new antibiotics are now available for the treatment of SCAP. Vena and colleagues from Bassetti's group review this topic, proposing “new algorithms” for SCAP treatment.

Biomarkers measured in plasma can help guide initial antibiotic treatment and assist in the de-escalation and duration of antibiotic treatment. Pedro Povoa and Jorge Salluh review the available evidence for their use in clinical practice, mainly for C-reactive protein and procalcitonin.

Viral pneumonia is a tremendous challenge for clinicians facing SCAP. With the implementation of rapid molecular techniques during the COVID-19 pandemic, we now know that viral SCAP is much more frequent than we thought. Unfortunately, only COVID-19 and influenza have specific antiviral treatments. Other viruses in SCAP can only be managed by supportive treatment. Cilloniz and colleagues from my group review the epidemiology and management of viral SCAP from influenza to COVID-19.

Failure of antibiotic treatment and clinical stability are important concepts. Treatment failure is still poorly defined, with up to 30% of patients showing treatment failure. The different causes of treatment failure and their management are reviewed by Raul Mendez and Rosario Menendez. The concept of clinical stability is crucial for the clinical management of SCAP and randomized controlled trials (RCTs). Of particular interest in this treatment failure population is a rapid modification of antibiotics in case of initial inadequate antibiotic treatment and the correct management of complications such as empyema, cavitation, and systemic dissemination.

Aspiration pneumonia represents around 20% of SCAP. The majority of these SCAP cases do not have a microbial definition. The mortality of SCAP patients is higher compared with patients without aspiration. Definitions, microbial issues, and empirical treatment are reviewed by Prof. Niederman's group. Of particular importance is the recommendation of avoiding, in most cases, anti-anaerobic treatments that can cause more harm than benefit. This recommendation aligns with the ATS/IDSA 2019 and SCAP European 2023 guidelines.

In a proportion of SCAP patients ranging between 5 and 15%, “noncore” microorganisms such as gram-negative nonfermenters and Enterobacterales extended-spectrum β-lactamase (ESBL), and methicillin-resistant Staphylococcus aureus (MRSA), can cause SCAP. The standard antibiotic recommended treatments do not cover these microorganisms. Several prediction scores are published and validated, showing acceptable accuracy. Ceccato and colleagues from Artigas' group cover this important clinical problem of “noncore” microorganisms, including the best-targeted antibiotic treatment.

All guidelines for CAP and SCAP do not include immunosuppressed patients. The mortality of these patients can be very high. On the other hand, the incidence and prevalence of SCAP in immunosuppressed patients are increasing in recent years for several reasons. Prof. Azoulay's group updates this problem, covering epidemiology, microbial diagnosis, and antibiotic treatments.

Finally, we, both editors, summarize the contents and recommendations of the latest European Respiratory Society (ERS), European Society of Intensive Care Medicine (ESCIM), European Society of Clinical Microbiology and Infectious Diseases (ESCMID), and Latin American Thoracic Association (ALAT) guidelines published simultaneously in the European Respiratory Journal (ERJ) and Intensive Care Medicine (ICM). The final target of these guidelines is to decrease SCAP mortality and morbidity. The recommended measures are not very difficult to apply; however, the feasibility of their application, outcome modifications, and cost-effectiveness need to be demonstrated.

We want to express our extreme gratitude to all article contributors for their generosity in writing quality, top-notch, and updated reviews. We hope that this SCAP issue will be very useful for clinicians and researchers.

Article published online:
11 April 2024

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