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 require a confirmation of the initial diagnosis. Plague is a quarantinable diseases covered under international regulations. In the United States, reporting of suspicious cases and sending collected material to specialized labs and to the State Health Department are mandatory procedures.

The diagnosis of plague is confirmed only by the following 2 techniques

• Y. pestis antibody titers, requiring a 4x increase between the acute and the convalescent phases.
• Lysis of Y. pestis by unique bacteriophages in bacterial culture

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.Dennis, David (2009). Plague (PDF). Springer Science+Business Media. p. 597. ISBN DOI 10.1007/978-0-387-09843-2 28. Retrieved Jul 25 2014.

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.