The latest daily numbers on coronavirus cases in Scotland have not made it a pleasant read.
If you look at the hard numbers, it would be like that appear as if the country’s Covid-19 epidemic is spreading worse than ever.
So far, for three days this week, new records have been set for the most coronavirus cases reported within 24 hours – 486 on Wednesday, 558 on Friday, and 714 on Saturday.
With this deluge of numbers, so often huge every day, it can be difficult for the public to know what to make of them and to put them into context.
An essential part of this context is Covid-19 testing – and if cases have increased in the last few weeks and months, daily testing must also be done, and in a very extensive way.
None of this is easy and nowadays the Scottish Government̵
Fortunately, it is possible to make sense of it.
A short test story
When the pandemic first started in the UK in late February-March, the country lacked the capacity for mass testing and tracing that other nations were either ready or quick to set up.
Perhaps the UK and Scotland could have built this capacity quickly like others – but on March 12th we decided not to.
It was suspected that the coronavirus outbreak was too widespread in the community for the conventional public health approach of testing, tracking, and isolating all cases to work.
Scotland “should have resumed mass testing in March”
Unlike today, people with symptoms were simply told to stay home for seven days to try to get better.
In general, only those were tested who had deteriorated to the point where hospital treatment was required.
This meant that when the Scottish epidemic peaked in April, the country was actually only testing an average of 1,300 people a day – and sometimes significantly fewer.
That’s peanuts compared to the numbers released on most days today.
Meanwhile the Scottish and British Governments were Build up their testing capabilities, albeit not as quickly as some would like.
Their main weapon was the British government’s new regional test network, the majority of which were based in Scottish centers in the country’s airports.
But this separate branch of test data was causing all sorts of chaos for those who updated the Scottish Government tables, and by mid-June months ago, huge amounts of test results were thrown on them.
In early July, a slew of lagging data on home testing and nursing home testing was added belatedly to daily totals, meaning testing numbers in Scotland suddenly skyrocketed.
Since then, we have consistently looked for far higher test numbers than any earlier point in the pandemic.
They peaked in late August and early September. Nearly 30,000 tests were conducted across the country over several days, with around 16,000 Scots tested each time.
Since then, however, those numbers have dropped significantly, to an average of 17,000 daily tests in September – or about 7,400 people tested per day.
The difference between daily tests and newly tested people is related to the number of people who are repeatedly tested, e.g. B. Nursing home workers.
The reasons for the decline in testing over the past few weeks – given the government’s call to increase capacity further – are not entirely clear, but could be related to problems the UK test booking portal had in meeting the rising demand.
Still, the increase in tests over time is unmistakable in the statistics.
On August 4, fewer than 375,000 people had been tested for coronavirus in Scotland.
Three quarters of a million Scots (about 14% of the population) had been tested by Friday – doubling the number in just seven weeks.
The positivity rate
As the first test chart above showed, the number of tests performed, as well as the number of people tested, can vary significantly from day to day.
Nicola Sturgeon says she is now first examining a different measure every morning to measure Covids prevalence in Scotland: the positivity rate.
This refers to the percentage of positive tests compared to the number of people newly tested.
US President Donald Trump, who tended to say the quiet part out loud, once said he wanted to see fewer tests in America because it would catch fewer cases.
But the downside of that is if you test a lot less but still find a lot of cases, your positivity rate will go through the roof.
For example, when Scotland had limited testing on April 18 and 411 positive tests were obtained from just 1,596 people who tested, the positivity rate was 26%.
For this reason, it only makes sense to look at the positivity measure if you have robust and consistent tests that are designed to capture all suspected cases.
Assuming such a system is According to the World Health Organization, a country keeps its epidemic largely under control when the positivity rate is below 5%.
Even as falls began to rise again in August, starting with the Aberdeen pub cluster, Scotland’s positivity rate stayed comfortably at the ballpark at 1%.
But that changed quickly in September as new outbreaks gained momentum in western Scotland and at universities.
Last Saturday (September 19th) the rate hit 5.3% and it jumped to 11.5% all week from that Saturday.
This will be of great concern to the First Minister and her advisors, if not more than the number of hard cases.
Second wave, or has it ever really disappeared?
Although cases have increased again in Scotland, the UK and Europe after a period when infections had subsided, some scientists are against using the term “second wave”.
A second wave, they argue, is the return of a virus that may have mutated into a new strain.
The first wave of Covid-19, it is argued, never really went – we just kept it locked up with the rest of us.
At first glance, this daily case graph suggests that it’s a second wave or spike, or whatever you want to call it, that is spreading more virulent than the first.
But the truth is, it is far too early to say for sure.
For starters, compared from September to April, we test an average of almost six times more people than back then.
It is clear that at the height of the first coronavirus wave in Scotland, hundreds, perhaps thousands, of daily cases were missing due to the more restricted testing regime.
And at the height of spring, it is believed that the R-number of Covid-19 in Scotland – the number of people each infected person infected – could be anywhere from four to six.
Currently the government estimates that the R number in Scotland is between 1.2 and 1.6.
Anything above is a cause for concern as the epidemic is growing rather than shrinking.
But it suggests that officials still don’t believe the virus is spreading the same exponential way it did five or six months ago.