Testing is our foremost weapon in the war against the coronavirus

Testing for Covid-19 infection is vital if we want to beat this disease without delay. When you are fighting an enemy you need to know your enemy, their strengths and their weaknesses. You must also know yourself. “That way you need not fear the result of a hundred battles,” ironically so says The

Art of War by Sun Tzu.

SARS-COV-2 is the name of the virus that causes Covid-19 infection. It is highly infectious by both droplet and aerosol spray. This means you can catch it by just talking to someone.

We are in the midst of a public health emergency the likes of which we have not seen in our lifetimes. Soon we will have a total lockdown and the hospitals will be overflowing with patients suffering from the pneumonia caused by this virus.

It is important to protect the health workers in the NHS so that they can continue to treat patients and save lives and also patients who are yet to catch the virus. If we do not? We have seen what is happening in Italy and in Spain. Social distancing and banning all unnecessary travel is one way to slow down the transmission, the young as well as the old are at risk and we need to consider that everyone is potentially infected.

But how can we be more definite, especially when it comes to medical personnel who are treating patients? We need to test NHS staff to see if they are infectious and whether they are going to be ill, in which case they should go home and isolate, and also to know when they are well and can come back to work. It is frightening in the front line and important to know if you have built up some immunity given the lack of adequate PPE (personal protective equipment).

Rapid testing kits are becoming available to check for infection – based on a technique known as PCR (polymerase chain reaction) which detects the virus’s genetic material in oral and nasal swabs.

These tests seem good and it is said that results are available in 45 to 50 minutes. However, this only tells us if the virus is present at that time, not if someone has had it in the past and has become immune. Serological testing can tell us this, and many of these tests have been developed and are becoming available. They are based on a technique known as Elisa (enzymelinked immunosorbent assay). This is a test that detects and measures

antibodies in your blood. It can be used to determine if you have antibodies related to the virus indicating past infection.

Antibodies are proteins that your body produces in response to harmful substances called antigens – in this case, the virus. In simple terms, in this test, some blood is mixed with the viral proteins and, if antibodies are present, they will bind to the protein and trigger a colour change, indicating past infection and hopefully immunity. This is not a test therefore for acutely ill patients, but a test that is taken retrospectively and can tell healthcare workers if they have had the disease.

There are two small problems, though: sensitivity and specificity. Sensitivity is the true positive rate (how many cases are correctly identified) and specificity relates to how many false positives there are.

Ideally a test must be 100 per cent sensitive and 100 per cent specific –

for what is being tested. There may well be some false positives on testing as these tests could potentially pick up other coronaviruses that just cause the common cold. So once we have a very specific test for Covid-19, and this is highly likely, it can be used to screen populations to see what the herd immunity is like and therefore herald an end to social distancing.

Also, and most importantly, it can be used to screen healthcare workers to see if they are immune.

One final thing: if there are people with high levels of circulating antibodies to the virus, having recovered, then blood components from these people (immune globulins) can be injected – after all the appropriate checks are done – into acutely ill people to neutralise the virus, and this would save lives.