Differential Diagnosis: For the bubonic form, tularemia adenitis, staphylococcal or streptococcal adenitis, meningococcemia, enteric gram-negative sepsis, cat scratch disease, and rickettsiosis should be considered. In tularemia or cat scratch disease, the inoculation site is usually more evident than in bubonic plague, and the patient will not usually be septic. The differential for pneumonic plague includes tularemia, anthrax, and staphylococcal enterotoxin B (SEB) inhalation. Continued deterioration without stabilization rules out SEB. The presence of a widened mediastinum on chest X-ray should alert the physician to the probability of anthrax. Patients with plague have a cough productive of bloody sputum, while those with tularemia generally have a nonproductive cough. For all of the infections above, early clinical suspicion, even without a definitive diagnosis, is key to prompt treatment and optimal patient outcomes.
Diagnostic tests: Presumptive diagnosis can be made microscopically by identification of the organism in smears from lymph node needle aspirate, sputum, blood, or cerebrospinal fluid by standard stains (Wright, Giemsa, or Wayson) or immunofluorescence. The organism is easily cultured or identified by PCR in blood, sputum, CSF, or bubo aspirates. Blood for PCR should be collected into 3-ml tubes with citrate, EDTA, or heparin. Vaccinated personnel should perform cultures in a BSL3 biocontainment facility.
Specimens of possible epidemiological interest include early postexposure (0-24 hours) nasal swabs, sputum, and induced respiratory secretions collected into plastic screw-cap containers for culture, and for fluorescent antibody (FA) assay. A four-fold rise in antibody titer in paired sera may also be epidemiologically useful.
Specimen Submission: All specimens must be triple contained, cold not frozen, in an approved shipping container and have biohazard labels. Before transport is arranged via a secure carrier, the receiving laboratory must be alerted prior to transport by calling 800-252-8239 ("press 1"). Newly available diagnostic tests may be discussed at that time. Specimens must be accompanied by a Specimen Submission Form (G-27A) and submitted to the Texas Department of State Health Services Laboratory, 1100 West 49th Street, Austin, TX 78756. For Plague/Yersinia pestis culture rule outs, plague/yersinia pestis must be mentioned on the G-27A form so that appropriate biosafety precautions will be taken in the laboratory.
Additional Tests: Chest x-ray reveals a patchy or confluent bronchopneumonia. Thrombocytopenia, leukocytosis, and elevated liver function tests (LFT) are common; fibrinogen-fibrin degradation products (DIC) may be noted.