The Health Service Executive (HSE) has adopted RNA PCR as the gold standard test for diagnosing Covid-19 cases, as part of the HSE test and trace strategy, consistent with international best practice, and approved by the National Public Health Emergency Team (NPHET). This platform is deployed in acute hospitals, the NVRL and HSE’s commercial partners. At present, the HSE has been able to provide adequate PCR testing for identified priorities in response to the very significant demand.
While rapid Antigen Detection Tests (ADTs) are described as rapid, and simple to perform, they are not designed to be delivered in large numbers and there are considerable human resource, operational, quality assurance, and clinical governance considerations in their administration. To date, validation work indicates that ADTs are most effective in detection of symptomatic cases, when symptom onset is within the last 5 days and when the likelihood of test positivity is greater than 10% among the target population. Validation studies, both here in Ireland and in Europe are showing significant disparities in test performance (particularly in relation to sensitivity) versus some manufacturer claims, with tests not meeting minimum performance requirements set by the World Health Organization and the European Centre for Disease Prevention and Control. Furthermore, their intended use is typically in symptomatic individuals in the early stages of infection, where samples are taken and tests conducted by trained health professionals. There is limited performance data currently available for the use of antigen tests in asymptomatic populations. The studies also show that performance in symptomatic individuals is much better than in asymptomatic individuals where data are available.
The NPHET (National Public Health Emergency Team) considers the use of ADTs on an ongoing basis and has endorsed recommendations on the use of ADTs that have been validated as a supplement to PCR testing in certain situations, and particularly when the availability of PCR tests may be limited.
The HSE is currently putting in place deployment options for the use of ADTs for specific indications in the acute hospital setting and as part of the response to outbreaks in the community setting in symptomatic vulnerable populations and their close contacts, supported by appropriate clinical governance and operational arrangements. This includes updating the case definition for SARS-CoV-2 to accept notification of positive results from ADTs undertaken in the public health system and reporting of such cases to the COVID Care tracker and to the Computerised Infectious Disease Reporting (CIDR) information system developed to manage the surveillance and control of infectious diseases in Ireland.
Considerable work has been undertaken to date to evaluate the use of ADTS in an Irish context and this will continue on an ongoing basis due to the role they can have in the national testing strategy. In particular, further setting-specific ADT validation work continues to be undertaken by the HSE. Antigen testing will not, however, replace the requirement for large scale PCR testing which remains the gold standard for community testing.
On an ongoing basis, NPHET considers and reviews, based on public health risk assessments, how best to target testing to detect, and mitigate the impact of, the virus across the population. This includes keeping Ireland’s national testing policy under continuing review.
