Atypical pneumonia

atypical pneumonia or walking pneumonia refers to pneumonia that is not caused by bacteria and other traditional pathogens. Currently the term atypical pneumonia has a greater relationship with the existing clinical difference compared to classical pneumonia. The five bacteria that most frequently cause this pathology are, in order from most to least frequent: Mycoplasma pneumoniae, Coxiella burnetti, Legionella pneumophila, Chlamydia pneumoniae and Chlamydia psitacci.

• Atypical pneumonia due to Legionela sp represents 2 to 6 % of pneumonia and has a higher mortality rate. Older adults, smokers and people with chronic diseases and weakened immune systems are at greater risk for this type of pneumonia.

It is usually seen in older people, smokers and patients with chronic and immunosuppressed diseases.

• Mycoplasm pneumonia is a type of atypical pneumonia and is caused by bacteria M. pneumoniae. This type of pneumonia usually affects people under the age of 40.

• Pneumonia due to bacteria related to Chlamydia occurs all year round and represents 5 to 15% of all pneumonia.

In 1981, the toxic syndrome caused in Spain by the ingestion of denatured rapeseed oil was diagnosed in its early stages as an outbreak of atypical pneumonia.

Causes

Atypical pneumonia is caused by microorganisms such as: Legionella pneumophila, Mycoplasma pneumoniae, Chlamydophila pneumoniae and Coxiella burnetii. Although atypical pneumonias have commonly been associated with milder forms of pneumonia, Legionella pneumonia, in particular, can be very serious and lead to high mortality rates.

The SARS virus was recently classified as atypical pneumonia while work was underway to isolate the pathogen.

Also at the end of April and beginning of May 2009 in Mexico there was an outbreak of a mutation of Human Influenza A H1N1, which affected the population and it was diagnosed that deaths from this virus were due to atypical pneumonia.

Symptoms and clinical picture

Unlike the classic picture of pneumonia (fever, cough and stitching pain), the atypical form also has a series of sensitive but not very specific patterns:

• Lack of response to common antibiotics (b-lactam).
• Lack of lung condensation symptoms.
• Absence of leucocytosis.
• Extrapulmonary symptoms.
• Dry cough without expectation.
• Little elveolar exudate.