Laboratory Studies
Complete blood count
The white blood cell (WBC) count may be markedly elevated to levels of 20,000/μL or greater. Usually, a shift to the left is noted. In late septic shock, the WBC count may be low.
Urinalysis
Urinalysis may demonstrate gross hematuria, red blood cell casts, and proteinuria. Rapid urine dipstick tests have been developed to screen for Yersiniapestis antigen and can be used in the field for rapid identification during outbreak situations.
Arterial blood gas
Arterial blood gas level may reveal hypoxia and/or acidosis.
Peripheral blood smear
Y pestis coccobacillus may be identified on peripheral blood smears in up to 20% of patients, according to some studies
Gram stain
Gram stain may identify the gram-negative, pleomorphic coccobacillus. Gram stain can be performed on bubo aspirate, sputum, and blood.
In 70% of patients, the gram-negative, bipolar-stained coccobacillus is visualized if present. When stained with Wayson or Giemsa stain, a bipolar safety pin structure may be identified. While Wright stain often demonstrates this characteristic appearance, shown in the image below, Giemsa and Wayson stains most consistently highlight this pattern.
Wright stain peripheral blood smear of patient with septicemic plague demonstrating bipolar, safety pin staining of Yersinia pestis. While Wright stain often demonstrates this characteristic appearance, Giemsa and Wayson stains most consistently highlight this pattern. Courtesy of Jack Poland, PhD, CDC, Fort Collins, CO.
Cultures of blood, sputum and bubo aspirate
The plague bacillus grows readily on most culture media. Features of culture are as follows:
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Growth is slow and may require more than 48 hours before identification of colonies is possible
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Optimal growth occurs at 28°C
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Blood culture results are positive in 85-96% of patients
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Bubo aspirate culture results are positive in 80-85% of patients
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Sputum culture results are positive only if lung involvement is present
Imaging Studies
Chest radiography
In patients with pneumonic plague, chest radiographs typically show alveolar infiltrates, with or without hilar lymphadenopathy. Bilateral consolidation may be evidenced. The radiograph below shows a patient with plague pneumonia.
Right-side middle and lower lobe involvement in a patient with plague pneumonia. No chest radiograph pattern is characteristic of plague, but bilateral interstitial infiltrates are most commonly seen. Courtesy of Jack Poland, PhD, CDC, Fort Collins, CO.
Other Tests
Specialized diagnostic testing is available at some laboratories, such as state health departments or the Centers for Disease Control and Prevention (CDC).
An F1 antigen rapid diagnostic test using monoclonal antibodies has shown promise in the early detection of the plague. [22]
Y pestis fluorescent antibody stain
This stain is performed on blood, sputum, or bubo aspirate samples. It may provide rapid diagnosis if available. If unavailable, send specimens to the CDC, Plague Branch, PO Box 2087, Fort Collins, CO 80522.
Y pestis fluorescent antibody titer
Acute and convalescent passive hemagglutination (PHA) titers should be taken 10 days apart. A 4-fold difference or a single convalescent PHA titer of 1:16 is evidence of infection.
Procedures
Needle aspiration of a bubo
The diagnosis may be made by Gram stain and culture of the aspirate. One may attempt aspiration even if the lymph node is hard and nonfluctuant. Infusion of 1-3 mL of normal saline in the aspiration site prior to aspiration may prove beneficial. Strict contact and respiratory precautions must be practiced to avoid spreading this highly contagious agent.
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Wright stain peripheral blood smear of patient with septicemic plague demonstrating bipolar, safety pin staining of Yersinia pestis. While Wright stain often demonstrates this characteristic appearance, Giemsa and Wayson stains most consistently highlight this pattern. Courtesy of Jack Poland, PhD, CDC, Fort Collins, CO.
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Here a flea is shown with a blocked proventriculus, equivalent to the gastroesophageal region in man. In nature, this flea would develop a ravenous hunger because of its inability to digest the fibrinoid mass of blood and bacteria. Subsequent biting of the nearest mammal results in clearing of the proventriculus through regurgitation of thousands of bacteria into the bite wound. Courtesy of United States Army Environmental Hygiene Agency.
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A suppurative bubo of the femoral lymph node is shown here. This is the most common site of erythematous, tender, swollen, nodes in a plague victim. The next most common lymph node regions involved are the inguinal, axillary, and cervical areas. Bubo location is primarily a function of the region of the body in which an infected flea inoculates plague bacilli. Courtesy of Jack Poland, PhD, CDC, Fort Collins, CO.
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The child in this photo has an erythematous, eroded, crusting, necrotic ulcer on the left upper quadrant of the abdomen, which is presumably the primary inoculation site of plague bacilli from the bite of an infected flea. This type of lesion is uncommonly found in patients with plague. Courtesy of Jack Poland, PhD, CDC, Fort Collins, CO.
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Ecchymoses at the neck base of a girl with plague. Bandage is over the site of a prior bubo aspirate. These lesions probably gave rise to the title line of the nursery rhyme "Ring around the rosy." Courtesy of Jack Poland, PhD, CDC, Fort Collins, CO.
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Right-side middle and lower lobe involvement in a patient with plague pneumonia. No chest radiograph pattern is characteristic of plague, but bilateral interstitial infiltrates are most commonly seen. Courtesy of Jack Poland, PhD, CDC, Fort Collins, CO.
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Rock squirrel in extremis coughing blood-streaked sputum of pneumonic plague. Courtesy of Ken Gage, PhD, CDC, Fort Collins, CO.
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Acral necrosis of nose, lips, fingers (shown here) and toes (image below) and residual ecchymoses over both forearms in a patient recovering from bubonic plague that disseminated to blood and lungs. At one time, the patient's entire body was ecchymotic. Reprinted from McGovern TW, Friedlander AM. Plague. In: Sidell FR, Takafuji ET, Franz DR, eds. Medical Aspects of Chemical and Biological Warfare. Chapter 23 in: Zajtchuk R, Bellamy RF, eds. Textbook of Military Medicine. Washington, DC: US Department of the Army, Office of the Surgeon General, and Borden Institute; 1997: 493. Government publication, no copyright on photos.
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Acral necrosis of nose, lips, fingers (image above) and toes (shown here) and residual ecchymoses over both forearms in a patient recovering from bubonic plague that disseminated to blood and lungs. At one time, the patient's entire body was ecchymotic. Reprinted from McGovern TW, Friedlander AM. Plague. In: Sidell FR, Takafuji ET, Franz DR, eds. Medical Aspects of Chemical and Biological Warfare. Chapter 23 in: Zajtchuk R, Bellamy RF, eds. Textbook of Military Medicine. Washington, DC: US Department of the Army, Office of the Surgeon General, and Borden Institute; 1997: 493. Government publication, no copyright on photos.
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World distribution of plague cases, 2000-2009. From the Centers for Disease Control and Prevention (CDC), Atlanta, Ga.
