Yersinia pestis infection laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Laboratory Findings

Following a thorough history and physical exam, patients suspected to be infected by the plague, such as a patient presenting with fever living in an endemic region, require a confirmation of the initial diagnosis. Plague is a quarantinable diseases covered under international regulations. Patients with bubonic plague suspected to have secondary pneumonic plague should be placed in respiratory isolation until after 48 hours of effective antibiotic administration.

In the United States, reporting of suspicious cases and sending collected material to specialized labs with expertise in Plague testing and to the State Health Department are mandatory procedures.

Common laboratory findings may not always be present. They include the following:

Blood Work-Up

• Leukoyctosis and neutrophilia with left shift
• Thrombocytopenia
• Elevated D-dimer
• Elevated transaminase and bilirubin levels
• Elevated creatinine
• Hypoglycemia

Urine Work-Up

• Proteinuria

Peripheral Smear

• Rod-shaped bacteria on Giemsa stain and "safety pin" appearance on Wayson stain
• Toxic granulations and Dohle bodies

Gram Stain

• Small gram-negative coccobacilli

Culture of Fluids

• Positivity for Y. pestis

Cerebrospinal Fluid Analysis

• Pleocytosis with polymorphonuclear leukocyte predominance
• Limulus test confirms endotoxin

According to the "2014 Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue and Soft Tissue Infections", The diagnosis of plague is confirmed only by gram stain and culture of aspirated material from suppurative lymph node.

Collection of Samples

Collection of blood specimens, lymph node aspirates from buboes, sputum samples, and tracheal swabs are needed before the administration of antibiotics. Additionally, cerebrospinal fluid (CSF) collection is required in cases suspected to have meningeal complications of plague.

Blood Samples

Blood should be sent for analysis, culture, and peripheral smear.

• If clinically stable, at least 3 samples for culture within 45 minutes should be collected before antibiotic administration.
• Serological diagnosis using passive hemagglutination test (PHA) using Y. pestis F1 antigen. If samples are retrieved within 3-4 weeks of symptoms onset, serological confirmation is highly sensitive.

The use of rapid detection tests, such as ELISA and PCR assays to detect F1 antigen are not routinely used yet. However, they may be helpful to confirm cases of suspected plague when gold standard confirmatory tests are not available.

Lymph Node Aspiration

Bubo aspiration, using a small sterile syringe containing sterile saline, is performed by insertion of the needle into the central part of the bubo. If original aspiration fails, injection of the sterile saline inside the syringe may be performed and then aspirated. The aspirate is then used as follows

• 2 slide preparations for routine staining, using Giemsa (or Wayson) method and for gram stain.
• 2 slide preparations for direct fluorescent antibody (FA) testing

Aspirate should also be used for culture using sheep blood agar, brain-heart infusion (BHI) broth, and MacConkey agar.

Other Specimens

All aspirates and specimens from CSF, tracheal swab, and sputum also need to be tested using gram stain, Giemsa stain, and FA testing.