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Atypical pneumonia due to Mycoplasma and Chlamydophila usually cause milder forms of pneumonia and are characterized by a more drawn out course of symptoms unlike other forms of pneumonia which can come on more quickly with more severe early symptoms.
Mycoplasma pneumonia often affects younger people and may be associated with symptoms outside of the lungs (such as anemia and rashes), and neurological syndromes (such as meningitis, myelitis, and encephalitis). Severe forms of Mycoplasma pneumonia have been described in all age groups.
Chlamydophila pneumonia occurs year round and accounts for 5-15% of all pneumonias. It is usually mild with a low mortality rate. In contrast, atypical pneumonia due to Legionella accounts for 2-6% of pneumonias and has a higher mortality rate.
Elderly individuals, smokers, and people with chronic illnesses and weakened immune systems are at higher risk for this type of pneumonia. Contact with contaminated aerosol systems (like infected air conditioning systems) has also been associated with pneumonia due to Legionella.
Factors that are associated with increased risk of contracting Atypical Pneumonia in infants include the following:
- Low socioeconomic status
- Young maternal age
- Multiple maternal sex partners
- Unmarried maternal status
- Exposure to other children at home or in daycare
- Exposure to secondhand smoke
Mycoplasma pneumoniae causes a wide range of respiratory infections, including pneumonia, tracheobronchitis, and upper respiratory tract infection. Only 3 to 10 percent of persons infected with M. pneumoniae develop pneumonia.5 Because Atypical pneumoniae infection becomes more common with increasing age, it is particularly important to consider this agent in elderly patients.
Atypical pneumoniae infection occurs throughout the year but can cause periodic outbreaks within small communities. Transmission is by person-to-person contact, and infection spreads slowly, most often within closed populations (e.g., households, schools, businesses).
The clinical course of pneumonia caused by M. pneumoniae is usually mild and self-limited. The mortality rate is approximately 1.4 percent. However, pulmonary complications can be significant and include effusion, empyema, pneumothorax, and respiratory distress syndrome.
Atypical pneumoniae infection may be associated with several extrapulmonary manifestations. Skin manifestations include erythema multiforme, erythema nodosum, maculopapular and vesicular eruptions, and urticaria. Neurologic derangements include aseptic meningitis, cerebral ataxia, encephalitis, Guillain-Barré syndrome, and transverse myelitis. The production of cold agglutinins can result in hemolytic anemia, especially when M. pneumoniae titers are high. Finally, complications such as myocarditis, pancreatitis, pericarditis, and polyarthritis can occur.
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