Coronavirus in Scotland: Four numbers to watch
As new confirmed cases of coronavirus continue to rise in most areas of Scotland, how worried should we be? Here are four figures to watch over the coming days and weeks.
1. The rate at which the virus spreads
The R number – also known as the R-value or reproduction number – is a key number that will be crucial to any decisions around lockdown restrictions.
It's a way of rating any disease's ability to spread and refers to the average number of people an individual would be expected to infect.
The higher the number, the more out of control a disease is.
If the reproduction number is higher than one, then the number of cases increases exponentially.
But if the number is lower the disease will eventually stop spreading, as not enough new people are being infected to sustain the outbreak.
Tracking Scotland's R number
The Scottish government has been monitoring the estimated R number in Scotland since the start of the outbreak.
Experts believe the number could have risen above one in mid-August. It is currently estimated to be between 1.1 and 1.4.
This compares with an estimate of between 4.3 and 5.8 at the end of February before any lockdown restrictions were put in place.
2. The number of positive cases
Any chart showing the number of daily confirmed Covid-19 cases in Scotland since February has, by now, a very familiar shape.
It rises quickly to a peak in early April, plateaus briefly, before declining at a slower rate and reaching lower levels for several weeks over the summer.
The line begins to curve upwards again at the end of July – at first in a series of steps, but quickly getting steeper.
New confirmed cases of Covid-19
The graph looks alarming – but there is another factor to take into account to give the figures context.
Testing strategy has changed radically in Scotland since the peak of the outbreak in April. There is now widespread community testing and many more people are being tested.
As a comparison, 1,209 people were tested on 15 April, but six times that number were tested on 16 September.
If more people are tested, more positive cases will likely be found – which is why it's also important to look at the percentage of positive cases.
Positive results for coronavirus
The percentage of tests coming back positive has decreased since the height of the outbreak – despite more tests being carried out. This is down to prevalence of the virus in the community decreasing.
The World Health Organisation says one measure that can indicate whether an epidemic is under control is whether – with a comprehensive testing system – less than 5% of samples return a positive result for Covid-19 over two weeks.
The last time the percentage of positive cases was above 5% in Scotland was in May, but it has been creeping up again in recent days and reached 4% on Thursday.
The Scottish government will be watching this figure carefully and may react if it goes above 5% for a sustained period.
3. The number in hospital
Although the number of positive cases has been rising steeply, there doesn't appear to be a corresponding increase in the number of Covid-19 patients in hospital.
One reason for this could be that younger age groups, who are much less likely to need hospital care, now account for the majority of new cases.
At its peak, the coronavirus outbreak created a huge load on Scotland's hospitals, with 1,520 Covid patients being treated across the country on 20 April.
Numbers mainly declined until the end of July and then fluctuated between 240 and 275 for several weeks.
However, the Scottish government has now changed the way it counts the total number of coronavirus patients in hospital on a given day, which makes it difficult to draw conclusions from this figure.
Instead, looking at the daily Covid-19 admissions to Scottish hospitals, it is possible to see that numbers are clearly down from the peak, but have shown a slight rise in the last few weeks.