History and exam

Key diagnostic factors

Many patients with atypical bacterial pneumonia will be younger than 50 years.

In many cases, patients will complain about persistent cough that does not resolve with time.

The presence of a dry cough should prompt suspicion that an atypical pathogen is present.

Prolonged time from onset of symptoms to the presentation can suggest atypical bacterial pneumonia.

Other diagnostic factors

A history of exposure to someone with respiratory infection is a risk factor for atypical bacterial pneumonia.

In many cases of pneumonia due to Mycoplasma pneumoniae and Coxiella burnettii pneumonia, pharyngitis and hoarseness will be present as well.

Fever, if present, is usually low grade.

Headache may accompany Mycoplasma pneumoniae and Chlamydophila pneumoniae infections.

Diarrhea may accompany Legionella infections.

Bullous myringitis is rare sign that suggests Mycoplasma pneumoniae infection.

Clinical signs of pneumonia may be mild or absent.

A mainly self-limited maculopapular or vesicular rash can accompany Mycoplasma pneumoniae pneumonia.

Risk factors

Many studies have shown that exposure to Mycoplasma pneumoniae and Chlamydophila pneumoniae in close community settings such as boarding schools, college dormitories, army basic training camps, or even hospitals can lead to outbreaks of infection with these pathogens.[5][30] This takes place mainly by person-to-person transmission among people in close proximity to each other.

Immunosuppression is associated with Legionella pneumophila infection. Affected patients seem to be highly susceptible to the disease, probably because of reduced ability to eradicate the intracellular pathogen.[14][15][31]

A few studies have shown that people who smoke are at greater risk for developing pneumonia due to infection with Mycoplasma pneumoniae, Legionella pneumophila, and probably Coxiella burnetii.[7][8][13][21] This may be related to damage to ciliated epithelium and/or modification of the host immune response.

Chronic lung disease is mainly associated with Legionella pneumophila infection.[14][15][31]

Travel is associated with heightened risk for infections, probably related to exposure to new water sources that have not been used for a while. Standing water has a higher Legionella pneumophila load.[14][15][31] Risk factor for influenza and severe acute respiratory syndrome.

Men are at greater risk for infection, mainly with Legionella pneumophila.[14][15][31]

One prospective incidence study has shown a possible association between patients receiving tumor necrosis factor (TNF)-alpha antagonists and Legionella pneumophila pneumonia.[10]

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