Credit Corgenix, USA
The World Health Organization has announced their approval of the first rapid field test for Ebola, which reportedly returns a result in less than 15 minutes – and without the need for a full laboratory setup. Tests available until now (ELISA, PCR, virus isolation) require sophisticated laboratory equipment, trained technicians, and at least 12-24 hours to process.
The two main measures of the accuracy of a diagnostic test are sensitivity and specificity.
- Sensitivity is defined as the ability of a test to correctly identify individuals who have a given disease or condition.
- Specificity is defined as the ability of a test to exclude someone from having a disease or illness.
Although no lab test is 100% accurate, the trade off that we often see with rapid tests is a drop in sensitivity, the ability to identify the disease in an individual. The classic example being RIDTs (Rapid Influenza Detection Tests), which are only expected to correctly identify influenza about 70% of the time (see A Side By Side Comparison Of Rapid Influenza Tests).
This new test is purported to have a 92% sensitivity rate, which is pretty impressive.
It’s specificity – the ability to exclude uninfected cases – is a bit less at 85%, but still a respectable number for a rapid test. The big advantage here is not only the speed of diagnosis, but the ability to conduct tests in the field, without electricity or a full laboratory setup.
This from WHO:
19 February 2015
WHO has assessed and today listed the ReEBOV Antigen Rapid Test Kit (Corgenix, USA) as eligible for procurement to Ebola affected countries. The test was evaluated under WHO’s Emergency Assessment and Use, a procedure established to provide minimum quality, safety and performance assurance for diagnostic products in the context of the Ebola emergency.
Ebola is currently being tested in laboratories largely through the detection of the virus’s nucleic acid (genetic material), using commercial or in-house tests. Nucleic acid tests (NATs) are more accurate but are complex to use and require well-established laboratories and fully trained personnel. In addition, turn-around time can vary between 12 and 24 hours.
The ReEBOV Antigen Rapid Test, which can provide results within 15 minutes, is based on detection of the Ebola protein rather than nucleic acid. When compared with the results of a NAT previously listed by WHO and currently being used in the field (RealStar® Filovirus Screen RT-PCR Kit 1.0, altona Diagnostics GmbH), ReEBOV Antigen Rapid Test is able to correctly identify about 92% of Ebola infected patients and 85% of those not infected with the virus.
While less accurate, the antigen test is rapid, easy to perform and does not require electricity – it can therefore be used at lower health care facilities or in mobile units for patients in remote settings. Where possible, results from ReEBOV antigen Rapid Test Kit should be confirmed by testing a new blood sample using an approved Ebola NAT.