Saturday, 10 October 2020

A Second Wave in Europe

After a quiet summer Covid 19 infections are rising again and there is a surge in reported positive test results. In many countries in Europe restrictions are being progressively introduced which limit rights of assembly and affect businesses.

There are people, including some politicians and experts, who believe that this surge in reported cases is a result of the increased availability of testing, and still others who think that the tests used are too sensitive. They consider that the current tests over-report the incidence of the virus. This opinion has been picked up and amplified by social media to support the view that the measures taken to limit the spread of the virus are an over-reaction.

The surge is accompanied by an increase in hospitalizations and an as yet smaller increase in deaths associated with the virus, but since these are bound to take longer to become evident, they are not increasing as rapidly.

The PCR Test

The most commonly used test for Covid 19 is the PCR (polymerase chain reaction) test. This amplifies any virus RNA found on samples by going through numerous cycles of replication. The outcome of this process is that the tests are very sensitive and will detect very small amounts of virus. Some experts have been mis-quoted as saying that this results in 90% false positives and therefore the overall numbers of people testing positive is greatly inflated.  This is incorrect, but there is an ongoing debate among experts as to how many cycles should be employed before declaring a test positive or negative. 

False Positives

By definition if the test finds Covid 19 viral RNA it is a correct positive result regardless of the initial quantity of virus present and the number of cycles of replication. What the PCR test can’t do, however, is to determine whether an individual is infectious. This is done by clinical examination to try to ascertain whether an infected person is displaying symptoms that have been found to be correlated with infectiousness.  So since there is no test which predicts a patient’s response to infection by the Covid 19 virus and their infectiousness, anyone testing positive is advised to self isolate and wait out the course of their illness.

The Rate of Increase of Cases

It's obviously important for individuals who think that they are likely to have been infected to know their test status; so that they can take the steps necessary to protect their families, friends, colleagues and others. However, on a larger scale the exact total number of positive tests doesn’t matter.  It’s sufficient to see the exponentially rising trend, which is currently showing itself in several European countries including France and the UK.

Whilst one can argue about whether tests are correct or not, eventually the real world will intervene. We know that the rising rate of infections is already leading to a rise in hospitalizations. As an example, in Paris  at the 10th October 2020, the rate of tests returning positive results is 15.27% and the occupancy of intensive care beds is 39.1%. The latter is predicted to be at 100% by the end of October. There will inevitably be, in my opinion, a rising death rate in the near future as well as further restrictions.

One can only hope that improvements in the knowledge and treatment of Covid 19, and the availability of therapeutics, will reduce the incidence of severe illness and death for those unfortunate enough to have caught it. One can also hope for the early availability of effective vaccines which give long term protection, but regrettably we don’t know yet how long any immunity conferred by a vaccine, or even a previous infection, will last.