Diagnosis
How plague is diagnosed: tests and differential diagnosis
Quick answer
- Plague diagnosis starts with clinical suspicion combined with exposure history (fleas, rodents, travel to an endemic area or laboratory work).
- Main samples are the bubo aspirate, blood and sputum (in lung cases).
- Laboratory methods include bacterial culture, PCR, F1 antigen detection and serology.
- Treatment is started on suspicion, before laboratory confirmation, because the disease can progress rapidly.
The suspicion: clinical plus epidemiological
No single symptom confirms plague. Diagnosis begins when the clinical picture is compatible and there is an exposure factor: contact with rodents or fleas, handling animals, travel to an endemic area, or laboratory work with the bacterium. Reporting exposure history to a health professional is essential.
Which samples are collected
| Form | Main sample | Other samples |
|---|---|---|
| Bubonic | Bubo aspirate (incising the bubo is not recommended) | Blood |
| Septicemic | Blood | Bubo aspirate, if present |
| Pneumonic | Sputum or tracheal aspirate | Blood, cerebrospinal fluid in meningitis cases |
Biosafety
Suspected samples are handled in laboratories with an appropriate biosafety level. Culturing Yersinia pestis is done under specific containment conditions.
Laboratory tests
- Culture: the reference method, confirms the bacterium in clinical samples; requires a containment laboratory.
- PCR: detects the bacterium's genetic material and is fast and sensitive.
- F1 antigen detection: detects a capsule protein of Yersinia pestis; rapid dipstick versions are useful in remote areas.
- Serology: measures antibodies in two samples (acute and convalescent), mainly useful for retrospective investigation.
Treat before the result
Because plague can progress within days and is severe, antibiotics are started on suspicion, without waiting for test results. Laboratory confirmation afterwards adjusts management and guides public-health measures, but must not delay antibiotics.
Differential diagnosis
| Form | May be confused with |
|---|---|
| Bubonic | Tularemia, bacterial lymphadenitis, cat-scratch disease, lymphogranuloma venereum, appendicitis (for inguinal nodes), dengue, malaria |
| Septicemic | Sepsis from other causes, severe dengue, meningococcemia |
| Pneumonic | Severe pneumonia from other bacteria, influenza, COVID-19, tuberculosis |
It is precisely this similarity that makes exposure history so valuable: it separates plague from dozens of other febrile illnesses.
Frequently asked questions
Is there a rapid test for plague?
Yes. Rapid tests detect the F1 antigen of the bacterium, useful in remote areas and during outbreaks, alongside PCR and culture.
How long do results take?
It depends on the method: PCR can be available within hours, while culture takes longer. Because the disease is severe, treatment does not wait for results.
What is the F1 antigen?
It is a capsule protein of Yersinia pestis used as a diagnostic target, including in rapid dipstick tests.
What can plague be confused with?
With many febrile illnesses, such as tularemia, dengue, malaria, cat-scratch disease, sepsis from other causes and pneumonia. Exposure history helps differentiate.
Sources
Medical review
Review by a licensed health professional is being arranged. This educational content is based on reference sources (WHO, CDC and medical literature) and does not replace evaluation, diagnosis or treatment by a health professional.
How this content was produced
- Who
- Produced by the Equipe editorial do Peste.com.br, the editorial team responsible for gathering, verifying and classifying public information about plague (Yersinia pestis).
- How
- Information is compiled from official and scientific sources (WHO, CDC and national health authorities) and from recognised news outlets. Every statement is classified as confirmed, reported or unconfirmed, and each article lists its sources.
- Why
- To offer clear, source-based information in Portuguese about plague and to separate verified fact from rumour. This content is educational and does not replace medical advice.
- Medical review
- Review by a licensed health professional is being arranged; no credential is claimed until a real professional is credited.
- Last review
See our sources and methodology and the editorial team.A revisão por profissional de saúde habilitado está em processo de credenciamento. Assim que concluída, o nome e o registro serão informados nesta página e nos dados estruturados.