From the Guidelines
Atypical organisms are not routinely covered in mild community-acquired pneumonia (CAP) treatment because they are less common causes of mild CAP and empiric coverage is often unnecessary. The most recent and highest quality study, published in 2007 by the Infectious Diseases Society of America/American Thoracic Society, recommends outpatient treatment with a macrolide (such as azithromycin, clarithromycin, or erythromycin) or doxycycline for previously healthy patients with no risk factors for DRSP infection 1. This is because the most common pathogens identified in mild CAP are S. pneumoniae, M. pneumoniae, C. pneumoniae, and H. influenzae, and macrolides have activity against these pathogens.
Some key points to consider when treating mild CAP include:
- The importance of therapy for Mycoplasma infection and Chlamydophila infection in mild CAP has been debated, as many infections are self-limiting 1.
- Studies have shown that treatment of mild M. pneumoniae CAP reduces the morbidity of pneumonia and shortens the duration of symptoms, but the evidence to support specific treatment of these microorganisms in adults is lacking 1.
- Macrolides have been commonly prescribed for treatment of outpatients with CAP due to their activity against S. pneumoniae and atypical pathogens, but the use of fluoroquinolones is discouraged due to concerns about resistance 1.
In terms of treatment, a macrolide (such as azithromycin) or doxycycline is recommended as first-line therapy for mild CAP, as they target the most common bacterial pathogens and have a favorable risk-benefit profile 1. However, if a patient with mild CAP fails to improve after 48-72 hours of standard therapy, has specific risk factors, or if there is a community outbreak of an atypical pathogen, coverage may be expanded to include macrolides like azithromycin or respiratory fluoroquinolones.
From the FDA Drug Label
In the treatment of pneumonia, azithromycin has only been shown to be safe and effective in the treatment of community-acquired pneumonia due to Chlamydia pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae or Streptococcus pneumoniae in patients appropriate for oral therapy
The reason we don't cover atypical organisms in mild community acquired pneumonia with azithromycin is that azithromycin has only been shown to be safe and effective in treating community-acquired pneumonia due to specific organisms, including Chlamydia pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, and Streptococcus pneumoniae 2.
From the Research
Atypical Organisms in Mild Community Acquired Pneumonia
- Atypical organisms, such as Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella species, are common causes of community-acquired pneumonia (CAP) 3.
- However, the treatment of mild CAP often focuses on covering typical bacterial pathogens, such as Streptococcus pneumoniae and Haemophilus influenzae, rather than atypical organisms 4, 5.
- This approach is based on the fact that Streptococcus pneumoniae remains the most common cause of CAP, although its incidence is declining 5, 6.
- The use of empiric antibiotic therapy, such as β-lactam/macrolide combination therapy, is recommended for hospitalized patients with suspected bacterial CAP and without risk factors for resistant bacteria 4.
- The decision to cover atypical organisms is often based on the severity of the disease, the presence of risk factors for resistant bacteria, and local resistance patterns 3, 7.
- In mild cases of CAP, the risk of atypical organisms may be lower, and the focus is on covering typical bacterial pathogens 4, 5.
- However, it is essential to note that viral/bacterial coinfection is relatively common, and the identification of a virus by PCR does not necessarily allow for discontinuation of antibiotic therapy 5.