Plague Workup

Updated: Aug 13, 2021
  • Author: Venkat R Minnaganti, MD, FACP; Chief Editor: Michael Stuart Bronze, MD  more...
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Laboratory Studies

The possibility of plague should be strongly considered in febrile patients from endemic areas who have history of exposure to rodents. Rapid recognition of the classic symptoms of this disease and laboratory confirmation are essential to instituting lifesaving therapy.

Expertise in testing for plague bacilli is limited to reference laboratories in plague-endemic states and the CDC.

Leukocytosis with a predominance of neutrophils is observed, and the degree of leukocytosis is proportional to the severity of illness.

Peripheral blood smear shows toxic granulations and Dӧhle bodies.

Thrombocytopenia is common, and fibrin degradation product levels may be elevated.

Serum transaminases and bilirubin levels may be elevated.

Proteinuria may be present, and abnormalities in renal function have been associated.

Hypoglycemia may be observed.

Twenty-seven percent to 96% of blood cultures are positive for Y pestis in patients with bubonic plague and septicemic plague. [26] Microbiology staff should be informed of the possibility of Y pestis agents in samples so that they can take adequate precautions when handling specimens.

Y pestis may be observed on a peripheral blood smear. Smear stained with Wright-Giemsa reveals rod-shaped bacteria. A Wayson stain demonstrates the typical "safety pin" appearance (bipolar staining) of the bacterium. Gram stain shows small gram-negative coccobacilli.

Wayson stain showing the characteristic "safety pi Wayson stain showing the characteristic "safety pin" appearance of Yersinia pestis, the plague bacillus. Image courtesy of Centers for Disease Control and Prevention (CDC), Atlanta, Ga.

Lymph node aspirates often demonstrate Y pestis. In patients with pharyngeal plague, Y pestis is cultured from throat swabs.

Cerebrospinal fluid (CSF) analysis in meningeal plague may show pleocytosis with a predominance of polymorphonuclear leukocytes. [29] Gram stain of CSF may show plague bacilli.

Gram stain of sputum often reveals Y pestis.

Updated (2014) guidelines on the diagnosis and treatment of bubonic plague have been published by the Infectious Diseases Society of America (IDSA) (see Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections: 2014 Update by the Infectious Diseases Society of America). [30]


Imaging Studies

Chest radiography reveals patchy infiltrates, consolidation, or a persistent cavity in patients with pneumonic plague.

ECG reveals sinus tachycardia and ST-T changes.

Nuclear imaging may help localize areas of lymphadenitis and meningeal inflammation.


Other Tests

Direct immunofluorescence testing of fluid or cultures may aid in rapid diagnosis. A novel rapid diagnostic test capable of detecting miniscule amounts of Y pestis F1 antigen within 15 minutes has been developed and field tested in Madagascar. [31] This test yields 100% sensitivity and specificity for Y pestis and other Yersinia species.

A passive hemagglutination test (performed on serum from a patient in acute or convalescent stages) with a 16-fold or greater increase in titer (single titer) suggests plague infection. [24]

A 4-fold rise in antibody titers to the F-1 antigen of Y pestis also confirms infection. [21]

A polymerase chain reaction (PCR) using primers derived from Y pestis plasminogen activator gene has been used to detect the pathogen in fleas, but the application of this method in humans is still a matter of speculation. [32]



Aspiration of lymph node (bubo)

Inject 1 mL of sterile saline into the bubo with a 20-gauge needle; after withdrawing several times, aspirate the fluid. Gram stain of the aspirate reveals gram-negative coccobacilli and polymorphonuclear leucocytes.

Wayson stain (basic fuchsin-methylene blue, ethyl alcohol-phenol stain) of the aspirate shows plague bacilli as light-blue bacilli with dark-blue polar bodies.

Examination of the aspirate of the fluid from the inguinal lymph nodes shows a characteristic bipolar appearance that resembles a closed safety pin.

Lumbar puncture

Lumbar puncture is strongly recommended when meningeal plague is suspected.