Atypical pneumonia is pneumonia caused by Mycoplasma pneumoniae, Chlamydophila pneumoniae and Legionella pneumophila bacterial pathogens. Basically, the lung area that absorbs needed oxygen, the alveoli, get infected so pulmonary function decreases. Atypical micro-organisms are a relatively recent discovery in contrast to more commonly known bacteria discovered in the previous century. Atypical forms of pneumonia are usually community-acquired pneumonia (CAP); this specifies people who have not been hospitalized, so the infection is not hospital based, or nosocomial.
Micoplasma Pneumonia
Also known as "walking" pneumonia, this is a frequently mild form that occurs gradually over a period of 1 to 3 weeks with clinical signs similar to that of a cold or flu. Data show the prevalence of this type being 2% to over 30% in adults. Crowding is a risk factor because this type spreads quickly in environments such as schools and prisons. Another risk factor is age; specifically, this type frequently occurs in people under 40 with peak prevalence between 5 to 20 years. Only 5 to 10% of diagnosed patients actually develop full-blown pneumonia. A dry and slowly worsening cough is considered the primary symptom that must be present, since dry coughing is a major part of this disease. Other symptoms include flu-like symptoms with fever, malaise and a persistent runny nose and multi-site pain.
Chlamydophila Pneumonia
Chlamydophila pneumoniae, like mycoplasma pneumonia, is generally a mild form with a low mortality rate in comparison to Legionella. This type has 3 forms that are infectious to humans: C. pneumoniae, C. psittaci and C. trachomatis. This type causes an estimated 5 to 15% of community-acquired pneumonia diagnoses. An unusual infection caused by C. psittaci is ornithosis, or parrot fever, an infection transmitted from birds to humans. It is common in parrots and pigeons, and the incubation period is 5 to 15 days from the day of exposure. Asymptomatic birds shed the bacteria in their feces and people become infected by inhaling the droppings. Symptoms include blood-streaked sputum, dry cough and flu-like symptoms.
Legionella Pneumonia
Atypical Legionella pneumonia can be life-threatening and has a higher death rate than Mycoplasma or Chlamydophila pneumonias. Discovered during a 1976 American Legion convention in Philadelphia, people became ill from breathing in contaminated air from air conditioning. This type accounts for approximately 2 to 15% of community-acquired diagnoses. Those at particular risk include the elderly, chronic disease patients, smokers and immune function-compromised individuals. Legionella is common as a nosocomial infection; for example, a significantly high incidence of Legionella pneumonia occurs in head and neck surgery patients.
Virulence
Mycoplasma pneumonia cases usually resolve without complications and hospitalization is rare.
Chlamydophila infections can become systemic, but prognosis is good if treated properly.
Legionella has the greatest lethality with the highest mortality rate.
Bottom Line
Of the three types, Legionella is the most serious because it can cause death. Data show that mortality rates of nearly 50% exist for individuals who are not treated properly or who develop nosocomial Legionnaire's. Possible symptoms include blood-streaked sputum, fever, pain, confusion, ataxia and diarrhea. If these symptoms appear, it is urgent to get immediate attention and treatment.
References
- Cecil Medicine, 23rd ed; L. Goldman, D. Ausiello, W. Arend; 2007
- Nathional Library of Medicine
- Mayo Clinic: Pneumonia and Your Lungs
