CBRNE - Plague Workup

Updated: Apr 18, 2017
  • Author: Susan E Dufel, MD, FACEP; Chief Editor: Duane C Caneva, MD, MSc  more...
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Workup

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 wit 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:

  • Growth is slow and may require more than 48 hours before identification of colonies is possible
  • Optimal growth occurs at 28°C
  • Blood culture results are positive in 85-96% of patients
  • Bubo aspirate culture results are positive in 80-85% of patients
  • Sputum culture results are positive only if lung involvement is present
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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 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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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.

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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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