Yersinia infection

World Health Organization: plague case definition[28]World Health Organization. Operational guidelines on plague surveillance, diagnosis, prevention and control. 2010 [internet publication]. https://apps.who.int/iris/handle/10665/205593

Suspected case:

• Compatible clinical presentation; AND

• Consistent epidemiological features such as exposure to infected animals or humans and/or evidence of flea bites and/or residence in or travel to a known endemic focus within the previous 10 days.

Presumptive case:

• Meets the definition for a suspected case PLUS at least 2 of the 4 following tests must be positive:

  • Microscopy: material from bubo, blood, or sputum contains Gram-negative coccobacilli, bipolar after Wayson or Giemsa staining

  • F1 antigen detection in bubo aspirate, blood, or sputum;

  • A single anti-F1 serology without evidence of previous Yersinia pestis infection or vaccination;

  • Polymerase chain reaction (PCR) detection of Y. pestis in bubo aspirate, blood, or sputum.

Confirmed case:

• Meets the definition for a suspected case PLUS:

• An isolate from a clinical sample identified as Y pestis; colonial morphology and 2 of the 4 following tests must be positive:

  • Phage lysis of cultures at 20 to 25 °C and 37 °C

  • F1 antigen detection

  • PCR

  • Y pestis biochemical profile; or

• A fourfold difference in anti-F1 antibody titre in paired serum samples; or

• A positive rapid diagnostic test using immunochromatography to detect F1 antigen (in endemic areas when no other confirmatory test can be performed).

Centers for Disease Control and Prevention: plague (Yersinia pestis) 2020 case definition[36]Centers for Disease Control and Prevention. Plague (Yersinia pestis): 2020 case definition. April 2021 [internet publication]. https://ndc.services.cdc.gov/case-definitions/plague-2020

Laboratory criteria for diagnosis

• Presumptive:

  • Elevated serum antibody titre(s) to Y pestis fraction 1 (F1) antigen (without documented fourfold or greater change) in a patient with no history of plague vaccination, or

  • Detection of F1 antigen in a clinical specimen by fluorescent assay.

• Confirmatory:

  • Isolation of Y pestis from a clinical specimen, or

  • Fourfold or greater change in serum antibody titre to Y pestis F1 antigen.

Case classification

• Suspected:

  • A clinically compatible case without presumptive or confirmatory laboratory results.

  • Confirmed or presumptive laboratory evidence without any associated clinical evidence.

• Probable:

  • A clinically compatible case with presumptive laboratory results without epidemiological risk factors.

• Confirmed:

  • A clinically compatible case with confirmatory laboratory results.

  • A clinically compatible case with presumptive laboratory evidence and epidemiological risk factors.