When making a plague diagnosis, a doctor often begins with a physical exam and questions about a person's exposure to animals that are possible carriers of the plague bacteria, such as rabbits or rats. If the disease is suspected, additional tests are performed on blood and sputum samples. Because other diseases, like typhoid, share similar symptoms, a doctor often rules these out before making a firm plague diagnosis.
In order to make a plague diagnosis, the doctor will ask a number of questions about a person's medical history, including questions about:
- Medical conditions
- History of possible exposure to infected rodents, rabbits, or fleas
- Recent travel history.
The doctor will also perform a physical exam. During the exam, the doctor will look at the skin and listen to the lungs for signs of plague (see Symptoms of Plague). If the doctor has a high suspicion that a person has plague, he or she will recommend certain tests.
A healthcare provider can make a plague diagnosis by doing laboratory tests on a sample of blood or sputum (saliva and discharge from respiratory passages) or on fluid from a lymph node. One test can include looking at the sample under a microscope for evidence of plague bacteria (Yersinia pestis).
Several diseases share similar symptoms of plague. The doctor will consider these conditions and rule them out before making a plague diagnosis. These conditions include:
- Lymphyogranuloma vernereum (a sexually transmitted disease affecting the lymph system)
- Syphilis (a sexually transmitted disease)
- Shigellosis (an infectious disease typically caused by unsanitary conditions)
- Tularemia (a serious illness usually caused by animals)
- Cat scratch fever (a disease associated with being scratched by a cat)
- Typhoid fever (a life-threatening illness caused by Salmonella).