BY Dr Nick Brown, GP and North Wilts Covid lead.

I am sure that you have all heard about this and are wondering why don’t they just get on with it? – well, obviously this is not as straight forward as you might imagine. There are the usual problems about the availability of raw materials at a time when everybody wants or needs something – think toilet rolls, which doesn’t help, but there are other important issues.

Firstly one of the reasons why Covid-19 has spread so quickly is that this a is a completely new virus variant which originated in bats in China and because it has never circulated amongst humans before, we have no existing immunity. Medicine had a standing start in fighting this new threat.

There are a number of potential ways to test:

1. For the presence of the virus in secretions/saliva. This is the basis of the current test – the PCR test . It may fail to detect the virus in up to 30 per cent of infected patients, sometimes due to virus levels being too low to detect at that time. It takes three to four days to process and may still test positive for a while after the virus has become inactive. There are some reports that a quicker test is becoming available.

2. Blood Antibody tests. These show that a patient has been exposed to the virus and is either mounting an immune response – Ig M or is possibly immune to further infection Ig G. This occurs perhaps one to two weeks after clinical infection and is part of clinical recovery. These tests, not yet available, in theory can be processed more quickly.

A very important question is what is the point of testing? A simple answer to that question is that testing must change what happens next.

The PCR test is too slow and possibly too inaccurate in early disease to change clinical management. There is no specific treatment proven to be effective against this virus and the treatment is about managing the complications as they occur.

A hospital patient with clinically suspected Covid needs to be nursed and isolated before the blood test result is known. A negative test may allow a patient to return more quickly to more normal circumstances – ie relaxing isolation, but given that the patient will have been initially looked after in a hospital Covid area, they may become infected during treatment and will need subsequent tests! If a positive test becomes negative, then the recovering patient is no longer infectious, and probably hasn’t been for a few days.

In the community, a negative PCR test would reduce the period of self-isolation by a day or two, again assuming it was accurate. Where a family is self-isolating for two weeks due to a suspected family member if the suspect turns out to test negative, then family self-isolation can stop. This is of particular relevance to health care workers as a majority of health workers are not self-isolating due to personal infection but possible family exposure.

At some stage, a decision will be made that restrictions can be lifted. This is the time when testing will be most valuable, particularly if an effective vaccine is not available. Patients who have high Ig G levels will have some immunity and perhaps will be safe from re-infection. For patients who have effectively self-isolated and haven’t been exposed and therefore have no immunity, this could be a dangerous time as Covid-19 is likely to continue circulating at a lower level for months or years to come.