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Diagnosis

Pontiac Fever

Pontiac fever can be confirmed by urine antigen or paired sera (blood specimens), but a negative test doesn’t rule out the diagnosis. It is often diagnosed clinically in the setting of other laboratory-confirmed legionellosis cases. Culture (isolating and growing the bacteria on special media) cannot be used to diagnose Pontiac fever.

Most people with Legionnaires' disease will have pneumonia (lung infection) since the Legionella bacteria grow and thrive in the lungs. Pneumonia is confirmed either by chest x-ray or on physical exam.

Several laboratory tests can be used to detect the Legionella bacteria within the body.


Urine Antigen Test

The most commonly used laboratory test for diagnosis is the urinary antigen test, which detects a part of the Legionella bacteria in urine (pee). If the patient has pneumonia and the test is positive, then the patient is considered to have Legionnaires' disease.


Culture

If the Legionella bacteria are cultured (isolated and grown on special media) from sputum (phlegm), a lung biopsy specimen, or various other sites, the diagnosis of Legionnaires’ disease is also considered confirmed.


Blood Specimens

Paired sera (blood specimens) that show a four-fold increase in antibody levels when drawn shortly after illness and several weeks following recovery, can also be used to confirm the diagnosis.

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