Intensive community PCR testing has been the main factor in completely suppressing outbreaks of Covid-19 infections in many locations throughout the world. Large-scale Covid-19 antigen testing has never had similar success. This does not mean that there is no role for Covid-19 antigen testing, but this role is evolving and only partially understood.

Internationally a debate between epidemiologists and infectious disease specialists regarding the relative merits of Covid-19 antigen and PCR testing has become circuitous, even antagonistic. This failure to achieve consensus on the relative roles of PCR and antigen testing is understandable. The situation itself – a new pandemic and for the first time the advent of large-scale PCR testing in the population – is novel and there are no epidemiological data regarding widespread testing from previous pandemics to act as a definitive guide.

Once the specimen arrives at and is introduced into the PCR machine in the laboratory the result becomes available in 35-60 minutes

Hospital Report

The only relevant epidemiological data on testing are those available within the current pandemic – evolving data which give some guide but a long way from allowing a definitive prescription. Thus a “best educated guess” approach has to be adopted. Advocates of intensive community-based PCR testing are countered by enthusiasts for antigen testing. The correct approach is likely to involve closely combining PCR and antigen testing; both have a role.

With community Covid-19 testing the main public health objective is to isolate and remove infectious persons as quickly as possible from contact with others – time is of the essence and of utmost importance in this process.

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Asymptomatic

Self-isolation by people exhibiting symptoms can occur immediately without testing, thereby reducing spread. But many infections are asymptomatic – especially in younger age groups, particularly schoolchildren.

Even amongst people displaying symptoms there may often be an understandable ambivalence to self-isolation as early symptoms may be atypical or vague and self-diagnosis inaccurate and biased.

Thus rapid access (ideally walk-in or drive-in) testing, with results 4-8 hours after swabbing, supports rapid self-isolation, particularly by the asymptomatic and vaguely symptomatic.

Apart from speed, the other important aspect of testing is its accuracy. PCR testing is the “gold standard” test for the diagnosis of Covid-19, with an accuracy (positive predictive value) approaching 100 per cent. Antigen testing is substantially less accurate than PCR testing. Thus PCR testing is accurate, but with current processes there is frequently a delay of 24 hours or more before the result becomes available to those tested.

Antigen testing is fast but lacks accuracy. The accuracy of antigen testing can be enhanced by performing serial tests and defining the environmental context of the testing along with symptom evaluation – but these slow down the emergence of a definitive result. With current processes PCR testing is slowish. The main delays with PCR testing involve transport of the specimen to the laboratory and operational downtime in the laboratory, that is, delay due to not being operational 24 hours a day. Once the specimen arrives at and is introduced into the PCR machine in the laboratory the result becomes available in 35-60 minutes. Delivery of the result can then occur immediately by electronic means if these processes and quality control are streamlined.

Sample transport

What has not received much publicity in Ireland is on-site dedicated local PCR testing, which can eliminate the need for sample transport to a central laboratory, thereby producing fast and accurate results. A number of corporations manufacture PCR machines, no larger than a 20kg suitcase, suitable for on-site PCR testing.

On-site PCR testing can also be adapted for mobile testing stations which can be deployed in situations such a school outbreaks. The main concern with on-site PCR testing is quality control standardisation with different operators in different locations. However, this difficulty can be readily overcome if there is intense, focused training, over a few days, of operatives who could be recruited from the ranks of science, biomedical, pharmacy, nursing and laboratory graduates. The logistics success of the vaccination programme can be repeated in a testing programme.

We have seen with the vaccination programme here in Ireland that where there is a will, many things can be achieved

In an Irish context it would not be wise to put our Covid-19 testing eggs into the one basket. Laboratory-based PCR testing, on-site PCR testing and antigen testing should all be expanded. On the streets of many towns and cities of continental Europe (especially France and Denmark) there are numerous walk-in testing stations where citizens can get an antigen test administered by a professional and have a result delivered to their phone in about 15 minutes.

Databases

Home-based self-administered kit antigen tests have a role to play, but people often prefer professionally administered tests, the results of which are immediately available to the individual tested and to epidemiological databases. With self-administered home kits, results may or may not be forwarded to databases, as has been the experience in the UK.

Early in 2021 the UK test and trace effort acquired close to one billion antigen testing kits from Chinese manufacturers. Supply of antigen test kits in the US has become severely constrained in recent weeks due mostly to increased workplace demand and aversion to Chinese supplies. In Ireland it would be wise to roll out all three testing modalities (central laboratory-based PCR testing, on-site PCR testing and antigen testing) not least so supply vagaries can be adapted to.

On-site PCR testing logistics are not well developed, but we have seen with the vaccination programme here in Ireland that where there is a will, many things can be achieved. Intensive testing will not eliminate the pandemic but it will slow down its development, protect the vulnerable and reduce personal and societal restrictions, as evidenced in countries on continental Europe and in the Far East.

In December 2020 the Irish test-and-trace system became overwhelmed and the health service almost became overwhelmed in January and February 2021. We must ensure this does not happen to us again by immediately enhancing our test-and-trace efforts.