A number of new diagnostic tests for SARS CoV2 are being and will be launched in the coming weeks with rapid point of care antigen tests being the most important technological innovation. Some months ago, the US Federal Drug Administration approved the first rapid antigen tests for sale in the United States. It only takes 15 minutes to diagnose COVID with these antigen detection tests and, in most cases, the result can be read out using a portable device the size of a mobile phone.
Rapid antigen tests are immunoassays using lateral flow chromatography which detect the presence of a certain viral antigen and signal infection. These tests are currently performed using a nasal or nasopharyngeal swab. These point of care tests are simple, but they must always be performed by a healthcare professional.
They are slightly less sensitive and specific than PCR (Polymerase chain reaction) but they have many other advantages:
– They don’t need a complex laboratory technique.
– Results can be ready in 15 minutes, allowing clinical decisions to be made at once.
– They are more than three times cheaper than PCR.
The US government has bought millions of these tests, especially for nursing homes.
Some of these portable rapid diagnostic systems include flu tests. Basically, this means that 2 tests can be obtained simultaneously, one for flu and another for COVID, and in 15 minutes it is possible to check if a symptomatic patient has flu, COVID or both. When the flu season arrives, this diagnostic capacity may prove to be crucial in the emergency services of hospitals, primary care, nursing homes, schools, etc.
The WHO published the document “Antigen-detection in the diagnosis of SARS CoV2 infections using rapid immunoassays. Interim guidance.” on 11 September 2020. The guidance recommends the use of rapid antigen tests for SARS CoV2 in the following situations:
a) To respond to suspected outbreaks of COVID-19 in remote settings, institutions and semi-closed communities where NAATs (nucleic acid amplification tests) are not immediately available;
b) To support outbreak investigations (e.g. in closed or semi-closed groups including schools, care homes, cruise ships, prisons, work-places and dormitories, etc.);
c) To monitor trends in disease incidence in communities, and particularly among essential workers and health workers during outbreaks or in regions of widespread community transmission where the positive predictive value and negative predictive value of an antigen-detecting rapid diagnostic test (Ag-RDT) result is sufficient to enable effective infection control; and
d) Where there is widespread community transmission, rapid diagonistic tests (RDTs) may be used for early detection and isolation of positive cases in health facilities, COVID-19 testing centres/sites, care homes, prisons, schools, with front-line and healthcare workers and for contact tracing.
The European Centre for Disease Prevention and Control (ECDC) published the document “COVID -19 testing strategies and objectives.” on 18 September 2020. In this guidance ECDC includes the use of rapid antigen tests to detect COVID-19 infection: ”Both NAATs and antigen tests can be used to detect ongoing infection, and WHO’s interim guidelines specify using an NAAT to confirm a COVID-19 case”.
Numerous European countries are currently validating these tests to incorporate them in their national strategies for pandemic preparedness, including the United Kingdom, Spain and the Netherlands.
These rapid antigen tests must be used under the same rules as for the use of PCR tests:
– The tests performed, and their results must be registered in the national health services’ monitoring and surveillance system; and
– The microbiology services must validate the test results in real life.
The following are critical characteristics that rapid point of care tests should meet to ensure that the stress of healthcare professionals is minimised in European Member States:
- There must not be any doubt about how to interpret the results. The device must provide the diagnostic result. Any tests where the healthcare professional has to visually interpret the result—taking into account the pressure they are under—should be avoided. The WHO, in its document “Antigen-detection in the diagnosis of SARS CoV2 infections using rapid immunoassays. Interim guidance.”, recognises the importance of this:“The use of a reader standardizes interpretation of test results, reducing variance in assay interpretation by different operators, but requires ancillary equipment.”
- The portable device must include connectivity, so that the results can be directly uploaded to the national health services’ monitoring and surveillance system. If systems lack connectivity, this can be a problem for traceability when registering the results of the diagnosis—and avoiding registration errors—in the surveillance and monitoring systems. Once again, healthcare professionals have to work under such pressure that any kind of manual task which does not directly help patients should be avoided.
- The chosen test platform should include SARS CoV2 and flu tests, and also respiratory syncytial virus preferably. This would mean the same platform could be used in primary care, emergency care, residential care, etc., encouraging health personnel to learn and become more efficient, once again taking into account the pressure they have to work under. This becomes even more important considering the ECDC guidance on COVID-19 testing included in its document ”COVID-19 testing strategies and objectives”, that under includes the following key message:
The European Biosafety Network calls on European Member States to ensure approval and supply of these new rapid antigen point of care tests as soon as possible as the benefits outline above of these tests is vital now for healthcare systems and professionals and the availability of those tests in the market will be limited.
