infectious diseases
Plague and Other Yersinia Infections
Diagnosis of Plague
Staining, cultures, and serologic and polymerase chain reaction (PCR) testing Rapid diagnosis of plague is important because mortality increases significantly the longer treatment is delayed. Diagnosis is made by stain and culture of the organism, typically by needle aspiration of a bubo (surgical drainage may disseminate the organism); blood and sputum cultures should also be obtained. Other tests include immunofluorescent staining and serology; a titer of>1:16 or a 4-fold rise between acute and convalescent titers is positive. PCR testing, if available, is diagnostic. Prior vaccination does not exclude plague; clinical illness may occur in vaccinated people. Patients with pulmonary symptoms or signs should have a chest x-ray, which shows a rapidly progressing pneumonia in pneumonic plague. The white blood cell count is usually 10,000 to 20,000/mcL (10 to 20 × 109/L) with numerous immature neutrophils. 