What is the difference between atypical pneumonia (walking pneumonia) and Community-Acquired Pneumonia (CAP)?

From the Guidelines

There is a significant difference between atypical pneumonia (walking pneumonia) and Community-Acquired Pneumonia (CAP), with walking pneumonia being a milder form of pneumonia that is a subset of CAP. Walking pneumonia is a non-medical term that refers to a milder form of pneumonia that doesn't typically require hospitalization, allowing patients to continue their daily activities while infected, hence the term "walking." It's most commonly caused by Mycoplasia pneumoniae bacteria. CAP, on the other hand, is a broader medical classification that includes any pneumonia contracted outside of a healthcare setting, as discussed in the guidelines by the Infectious Diseases Society of America (IDSA) and the American Thoracic Society (ATS) 1. CAP can range from mild to severe and can be caused by various pathogens including bacteria, viruses, and fungi.

Key differences between the two include:

• Severity: Walking pneumonia is generally milder, while CAP can range from mild to severe
• Causative organism: Walking pneumonia is often caused by Mycoplasia pneumoniae, while CAP can be caused by a variety of pathogens
• Treatment approach: Mild cases (walking pneumonia) often require only oral antibiotics, while more severe CAP may necessitate hospitalization, intravenous antibiotics, oxygen therapy, and supportive care
• Treatment setting: Walking pneumonia typically does not require hospitalization, while severe CAP may require hospitalization

According to the IDSA and ATS guidelines 1, the management of CAP should be guided by the severity of the disease, the presence of comorbidities, and the likelihood of specific pathogens. The guidelines are intended primarily for use by emergency medicine physicians, hospitalists, and primary care practitioners, and provide a framework for the evaluation and treatment of CAP. In general, walking pneumonia can be treated with oral antibiotics such as azithromycin or doxycycline, while more severe CAP may require more intensive treatment, including hospitalization and intravenous antibiotics.

From the FDA Drug Label

CLINICAL STUDIES Community-Acquired Pneumonia The presumed bacteriological outcomes at 10 to 14 days post-therapy for patients treated with azithromycin with evidence (serology and/or culture) of atypical pathogens for both trials were as follows: Evidence of Cure + Infection Total Cure Improved Improved Mycoplasma pneumoniae 18 11 (61%) 5 (28%) 16 (89%) Chlamydia pneumoniae 34 15 (44%) 13 (38%) 28 (82%) Legionella pneumophila 16 5 (31%) 8 (50%) 13 (81%)

The difference between atypical pneumonia (walking pneumonia) and Community-Acquired Pneumonia (CAP) is not explicitly stated in the provided text. However, it can be inferred that atypical pneumonia is caused by pathogens such as Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella pneumophila, whereas CAP can be caused by a variety of pathogens, including S. pneumoniae, H. influenzae, and M. catarrhalis.

• Atypical pneumonia is often referred to as "walking pneumonia" due to its typically milder symptoms.
• CAP is a broader term that encompasses pneumonia acquired outside of the hospital setting, and can be caused by a range of pathogens. The FDA drug label does not provide a direct comparison between the two conditions, and therefore, no definitive conclusion can be drawn 2.

From the Research

Definition and Diagnosis

• Community-Acquired Pneumonia (CAP) is diagnosed in a patient with 2 or more signs or symptoms of pneumonia in conjunction with consistent radiographic findings without an alternative explanation 3
• Atypical pneumonia, also known as "walking pneumonia", is often caused by Mycoplasma pneumoniae and can present with milder symptoms, but can still lead to severe disease in some cases

Causes and Risk Factors

• CAP can be caused by a variety of pathogens, including bacteria, viruses, and atypical organisms, with Streptococcus pneumoniae being the most commonly identified bacterial pathogen 3, 4
• Atypical organisms, such as Mycoplasma pneumoniae, are implicated in up to 40% of cases of CAP diagnoses 5
• Older adults, those with underlying lung disease, smoking, or immune suppression are at highest risk for CAP and complications of CAP 3

Treatment

• Empirical antibacterial therapy for CAP should consider disease severity and evaluate the likelihood of a bacterial infection or resistant infection, and risk of harm from overuse of antibacterial drugs 3
• Hospitalized patients without risk factors for resistant bacteria can be treated with β-lactam/macrolide combination therapy, such as ceftriaxone combined with azithromycin, for a minimum of 3 days 3
• For atypical pneumonia, treatment may include antibiotics such as doxycycline or azithromycin, but the need to start empirical therapy for these pathogens in low-severity CAP remains controversial 5, 4

Management and Guidelines

• The decision to hospitalize a patient with CAP is clinical and should be complemented with an objective tool for risk assessment, such as the Pneumonia Severity Index (PSI) or the CRB-65 6
• Guidelines for the management of CAP recommend against routinely adding steroids as an adjuvant treatment, and emphasize the importance of early appropriate antibiotic treatment and prevention of bacterial resistance 3, 6, 7