How Is Ebola Diagnosed? PCR Tests, Rapid Tests, and Clinical Criteria
A guide to Ebola diagnosis — from clinical recognition and sample collection to RT-PCR testing and point-of-care rapid tests. Explains why early diagnosis is critical and the challenges of testing in the field.
The Diagnostic Challenge
One of the most dangerous features of Ebola virus disease is how it looks like other diseases in its early stages. In the first 1–3 days, symptoms — fever, headache, fatigue, muscle pain — are indistinguishable from malaria, typhoid, lassa fever, or other common febrile illnesses in Central and West Africa. Clinically suspecting Ebola too early leads to over-triage and resource waste; suspecting it too late allows transmission to continue.
Getting the diagnosis right, fast, is one of the most critical determinants of outbreak control.
Clinical Case Definition: The First Filter
Before laboratory testing, clinicians use a clinical case definition to decide who to test. WHO’s standard suspect case definition requires:
A suspect case is ANY person, alive or dead, who has:
- Had contact with a suspected, probable, or confirmed EVD case AND has any of the following symptoms: sudden onset of fever, intense weakness, muscle pain, headache, or sore throat; OR
- Any two of: fever, vomiting, diarrhoea, abdominal pain, unexplained bleeding or bruising, difficulty swallowing
Epidemiological context is essential: a suspect case must have a plausible exposure — either contact with a known case, attendance at a funeral of an EVD victim, contact with an infected animal, or healthcare worker exposure in an active outbreak area.
In practice, any patient with fever and a potential exposure history in an active outbreak zone must be isolated and tested immediately.
Laboratory Confirmation: RT-PCR Is the Gold Standard
The definitive diagnostic test for Ebola is reverse transcriptase polymerase chain reaction (RT-PCR), which detects viral RNA from blood samples.
How RT-PCR Works
- A blood sample is collected from the suspect case (strict PPE required)
- RNA is extracted from the sample
- Specific primers targeting Ebola virus RNA sequences are used to amplify any viral RNA present
- Detection of amplified product (cycle threshold, or Ct value) confirms the diagnosis
RT-PCR is highly sensitive and specific — it can detect as few as a few hundred viral copies per millilitre of blood.
Timing Matters
RT-PCR is most reliable after symptom onset. In the very early incubation period (before symptoms), viral loads may be below the detection threshold even in someone who will develop disease. For this reason:
- A negative RT-PCR in the first 72 hours of symptoms does not definitively exclude Ebola — repeat testing after 72 hours may be needed
- Testing deceased patients is possible from oral swabs or blood specimens, with appropriate PPE
Specimen Types
- Whole blood (EDTA tube): preferred specimen for symptomatic patients
- Oral swabs: used for deceased patients or when blood collection is not feasible
- Urine: less sensitive than blood but useful as supplementary specimen
Sample Collection in the Field
In remote DRC outbreak areas, samples are transported to regional laboratories (typically INRB — Institut National de Recherche Biomédicale — or NCDC Nigeria for West Africa). The challenge:
- Triple packaging required for Category A infectious substances
- Cold chain maintenance
- Transport time: hours to days in remote areas
- This delay can mean a patient has progressed significantly before a diagnosis is confirmed
Rapid Diagnostic Tests (RDTs)
To address the delay problem, point-of-care rapid antigen detection tests for Ebola have been developed.
How RDTs Work
Like a COVID rapid antigen test, Ebola RDTs detect Ebola viral proteins (antigen) in blood or oral swabs, returning a result in 15–30 minutes without laboratory equipment.
Available Products
- OraQuick Ebola Rapid Antigen Test (OraSure Technologies): WHO Emergency Use Listing granted; can be used at point of care
- ReEBOV Antigen Rapid Test (Corgenix): used during the 2014–2016 West Africa epidemic under emergency protocols
Performance
RDTs are generally less sensitive than RT-PCR, particularly at low viral loads (early disease). A negative RDT does not rule out Ebola — it should be confirmed with RT-PCR. However, a positive RDT in an epidemic context is highly predictive and sufficient to initiate immediate isolation and treatment pending PCR confirmation.
RDTs are most useful for:
- Triage of large numbers of suspect cases in remote health posts
- Rapid screening in areas without laboratory access
- Quick decisions about isolation need while awaiting PCR
Mobile Laboratories: Closing the Gap
During major outbreaks, WHO and partners deploy mobile field laboratories close to the outbreak epicentre. In the 2018–2020 DRC Kivu outbreak, multiple mobile labs were positioned throughout North Kivu and Ituri, reducing turnaround time from days to 6–24 hours.
GeneXpert platforms (Cepheid) have been adapted for Ebola RT-PCR and are used in mobile lab configurations — the same platform used for TB and COVID-19 testing.
Differential Diagnosis: What Else Could It Be?
Before Ebola is confirmed, clinicians must consider (and ideally rule out) other causes of severe febrile illness, particularly:
| Disease | Distinguishing features |
|---|---|
| Malaria | Most common cause of fever in Central Africa; blood film or RDT |
| Typhoid | Slower onset, relative bradycardia, splenomegaly; blood culture |
| Lassa fever | West Africa; pharyngitis, hearing loss; specific PCR |
| Meningococcal disease | Purpuric rash, meningism; blood culture |
| Viral hepatitis | Jaundice; hepatitis panel |
| Septic shock | Bacterial source; blood cultures |
In practice, a patient with severe febrile illness and a potential Ebola exposure should be simultaneously tested and isolated — not held for Ebola testing while awaiting malaria results.
Genomic Sequencing: Beyond Diagnosis
Once Ebola is confirmed, whole genome sequencing provides additional critical information:
- Identifies the specific ebolavirus species (Zaire, Sudan, Bundibugyo, etc.)
- Reveals phylogenetic relationships — is this a new spillover from wildlife, or linked to a previous outbreak?
- Detects mutations that might affect vaccine or treatment efficacy
- Tracks transmission chains to identify superspreading events
The 2018–2020 DRC Kivu outbreak generated hundreds of genomes, enabling real-time phylogenetic analysis that revealed transmission dynamics and informed response targeting.
The 2026 DRC Outbreak: Diagnostic Response
In the current 2026 outbreak, INRB confirmed the initial cases using RT-PCR within 48 hours of sample receipt. Mobile laboratories have been deployed to North Kivu, and OraQuick RDTs are being used at community health posts in the affected health zones to accelerate triage.
Genomic sequencing confirmed a single transmission chain from a likely wildlife spillover event — consistent with the forest environment of Rutshuru territory.