History and exam

Key diagnostic factors

common

presence of risk factors

Key risk factors include close community settings and immunosuppression.

age <50 years

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

persistent cough

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

dry cough

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

long duration of symptoms

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

Other diagnostic factors

common

recent community exposure

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

throat involvement

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

uncommon

fever

Fever, if present, is usually low grade.

headache

Headache may accompany Mycoplasma pneumoniae and Chlamydophila pneumoniae infections.

diarrhoea

Non-bloody diarrhoea may accompany Legionella infections.

bullous myringitis

Bullous myringitis is rare sign that suggests Mycoplasma pneumoniae infection.

lung rales/crepitations

Clinical signs of pneumonia on physical examination may be mild or absent.

rash

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

Risk factors

strong

close community settings

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

Immunosuppression is an associated risk factor for Legionella pneumophila infection. Affected patients seem to be highly susceptible to the disease, usually due to their reduced ability to eradicate the intracellular pathogen.[14][15][31]

weak

cigarette smoking

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

Chronic lung disease is mainly a risk factor for Legionella pneumophila infection.[14][15][31]

travel

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]​ Frequent travel might predispose patients to influenza and/or newer SARS-CoV-2 strains.

male sex

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

immunomodulating drugs

One prospective incidence study has shown a possible association between patients receiving tumour necrosis factor (TNF)-alpha antagonists and Legionella pneumophila pneumonia.[12]​​

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