Clinical Pearls & Morning Reports
Published August 16, 2023
In the United States, community-acquired pneumonia is one of the leading causes of hospitalization and death, with approximately 6 million cases reported each year. Read the NEJM Clinical Practice Article here.
Q: What are some of the factors involved in the pathogenesis of pneumonia?
A: The development of pneumonia is influenced by a combination of factors, including host susceptibility, pathogen virulence, and the inoculum of microorganisms reaching the lower airways. Respiratory pathogens must overcome several defense mechanisms of the respiratory system before reaching the alveoli. Pathogens can reach the alveoli by means of microaspiration (aspiration of small amounts of oropharyngeal secretions that often occurs during sleep), inhalation, macroaspiration (aspiration of a large amount of oropharyngeal or upper gastrointestinal contents), or hematogenous spread. Microaspiration is the primary path for microorganisms into the lungs.
Q: Is microbiologic testing for bacterial causes recommended for patients who are treated for community-acquired pneumonia in ambulatory settings?
A: Microbiologic testing for bacterial causes is generally not recommended for most patients who are treated in ambulatory settings, since empirical antibiotic therapy is largely successful. However, testing for viruses (e.g., SARS-CoV-2 and influenza) should be considered, since the results can affect the choice of therapy.
A: The diagnosis is made on the basis of infiltrates shown on a chest radiograph (or on CT in a patient with symptoms if a chest radiograph is negative), plus supporting symptoms, signs consistent with airspace disease (e.g., rales, rhonchi, or egophony), or laboratory abnormalities resulting from the local and systemic inflammatory responses. Testing for the inflammatory biomarker procalcitonin may supplement clinical judgment with regard to diagnosis and course of bacterial community-acquired pneumonia, since synthesis of procalcitonin is triggered by specific cytokines in response to bacteria. Although the procalcitonin level is typically elevated in bacterial community-acquired pneumonia, it is low in viral community-acquired pneumonia. Procalcitonin levels quickly decline with the resolution of bacterial infection, a response that can inform the decision to discontinue treatment with antimicrobials. However, procalcitonin levels are not definite indicators, since false positives can occur (e.g., in hemorrhagic shock or kidney injury), and some bacteria (e.g., mycoplasma) may cause pneumonia in patients with normal procalcitonin levels.
A: The decision regarding the site of care depends on many variables, including severity of illness, associated disease, presence of hypoxemia, adequacy of home support, and probability of adherence to treatment. The severity of a patient’s illness is primarily a determination based on clinical judgment, which can be supplemented by the use of severity scores. The most commonly used severity scores are the Pneumonia Severity Index and CURB-65. The CURB-65 scale ranges from 0 to 5; scores are calculated by assigning 1 point each for the presence of new-onset confusion, blood urea nitrogen level greater than 19 mg per deciliter, respiratory rate greater than 30 breaths per minute, systolic blood pressure less than 90 mm Hg or diastolic blood pressure less than 60 mm Hg, and age of 65 years or older. Outpatient treatment is recommended for a patient with a CURB-65 score of 0 or 1, a short hospital stay or close observation should be considered for a patient with a score of 2, and hospitalization is recommended for a patient with a score of 3 to 5. Severity score thresholds have not been defined for the treatment of patients who are immunocompromised; thresholds for admission should be based on clinical judgment.