Knowing what happens at the clinic makes it easier to help it happen quickly.
1. The questions and the examination. The doctor asks about the last 10 days: where you have been, flea bites, animals, anyone ill near you, any antibiotics you have taken. Then the examination: temperature, breathing, blood pressure, and the lymph nodes of the groin, armpits and neck.
2. The samples. Which ones depends on the form:
- fluid drawn with a fine needle from the bubo;
- blood;
- sputum, if there is a cough.
Samples are taken before the first dose of antibiotic wherever that does not cause delay.
3. The tests.
- The rapid test. A strip that detects the F1 antigen of the bacterium in bubo fluid or sputum; the result is ready in 15 minutes. A review of the published studies found that it picks up nearly every true case, but that a positive result is wrong often enough to need confirming. It guides the first decisions; it does not settle the diagnosis.
- Microscopy. Under the microscope the stained bacteria look like closed safety pins. This is suggestive, not proof — other bacteria can look the same.
- Culture. Growing the bacterium from the sample is the reference method. It also shows which antibiotics work. It takes at least 4 days, plus the time needed to get the sample to a laboratory equipped for it.
- PCR. Detects the genetic material of the bacterium. Two different gene targets have to be positive for the result to count as confirmation.
- Antibodies. Two blood samples taken at least 2 weeks apart can show that the body has responded to the bacterium. This confirms a case afterwards; it does not help on the first day.
- A chest X-ray, when plague in the lungs is suspected.
4. Treatment does not wait for any of this. Antibiotics are started as soon as the samples are taken, on the strength of the symptoms and the history. The instruction of the United States Centers for Disease Control and Prevention to clinicians is written in capital letters: do not wait for diagnostic test results if you suspect plague.
5. The three words you may hear.
- Suspected: the symptoms fit and there was a possible exposure in the previous 10 days; no test yet.
- Probable: in addition, a first test is positive — the rapid test, microscopy, or a single antibody test.
- Confirmed: the bacterium has been grown, or its DNA found, or antibodies have risen between two samples.
6. The report. A suspected case is reported to the public-health authority at once. That is not a formality and not a penalty: it is how the people who were close to the patient are found and protected in time.
What this means for you. You may be treated for plague, and your contacts given preventive antibiotics, on a suspicion that the laboratory later rules out. That is the system working as designed, not an error.
Source. WHO, Manual for plague surveillance, diagnosis, prevention and control (2024), sections 4 and 5, https://www.who.int/publications/i/item/9789240090422 ; Jullien S., Dissanayake H. A., Chaplin M., "Rapid diagnostic tests for plague", Cochrane Database of Systematic Reviews 2020, Issue 6, https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD013459.pub2 ; United States Centers for Disease Control and Prevention, Clinical care of plague, https://www.cdc.gov/plague/hcp/clinical-care/index.html
What this is not. Reading, not a laboratory protocol. Which tests are done, and in what order, is decided by the clinicians and the laboratory of the country you are in.