ONLY one in every 200 Covid tests carried out in Scotland is now detecting a positive case, as the prevalence of the virus continues to fall.

The ratio of positive to negative test results indicates that Scotland “is on the safe side” in terms of controlling the pandemic, according to a scientific briefing paper that draws comparisons with the performance in New Zealand and South Korea.

It has also plunged since April, when more than one in five tests were coming back positive.

It came as Nicola Sturgeon confirmed that no deaths from Covid had been reported in Scotland for a second day in a row, with just 15 confirmed or suspected Covid patients in intensive care.

READ MORE: Is Scotland's slow and steady exit from lockdown already working?

The First Minister said the progress would enable her to give “more clarity” later this week on a timeline for the next steps out of lockdown.

For the first time, data covering the results from both NHS Scotland labs - which mainly process tests for hospital patients - and the UK Government-funded mobile and drive-thru testing centres has been made available online.

It shows that a total of 32,021 tests were processed in Scotland last week - June 15 to 21 - from which 155 cases of Covid were detected.

That positive case rate of 0.5 per cent compares to 22.6% between April 6 to 12 when 2,206 positive Covid cases were picked up from a total of 9,748 NHS lab tests.

Although drive-thru testing numbers are recorded from April 6 - totalling 975 tests in that first week - positive results from those sites have only been included in the total since June 15. 

Across the UK as a whole, around 1.9% of Covid tests are finding a positive case.

That compares to around 4.8% in the US, and 0.6% in Italy.

According to a background paper dated April 29 and drawn up by the UK Government’s scientific advisors to inform moves to a Test, Trace and Isolate Strategy - but also considered by the Scottish Government’s Covid Advisory Group - the percentage of positive Covid tests in a total sample is an important way of gauging the magnitude of the virus problem.

The paper adopted Germany’s criteria, which says that if more than 10% of your virus tests are producing a positive result you “have a problem”.

At less than 10%, the country is “getting a handle on the problem” and at around 5% “you are likely to be in control”.

By the time the positive rate falls to around 2% or less “you are on the safe side”, said the paper, noting that this was the benchmark set early in the pandemic by Covid success stories such as Taiwan, South Korea, Australia and New Zealand.

Fundamentally, the 'percentage positive' rate is considered to be an important thermometer of whether a country's testing regime is adequate to cope with the amount of virus spreading within its population.

The World Health Organization recommends that the rate should be below 5% for at least two weeks before countries begin to relax social distancing and other public health measures.

At the height of its Covid crisis, New York City had a positivity rate of 55% - a sign not only that it was the epicentre of the US outbreak, but also that the volume of testing was falling far short of what was needed.

READ MORE: Social care workers more than twice as likely to die from Covid as frontline NHS staff

However, even a test positivity rate of 20% - as Scotland had in April - is still considered very high by infectious disease experts, and a sign that testing is skewed towards hospitals and likely to be missing huge numbers of mild or asymptomatic cases in the community who are still able to pass it on.

Academics who compile daily Covid statistics for the website, Our World in Data, have highlighted the significance of driving down the percentage positive rate.

They wrote: "One important way to understand if countries are testing sufficiently is to ask: how many tests does a country do to find one Covid-19 case?

"We see enormous differences across countries.

"Some countries, like Australia, South Korea and Slovenia do hundreds, or even thousands of tests for each case they find.

"Others, such as Mexico and Nigeria, only do a handful of tests – five or fewer – for every confirmed case.

"Countries that do very few tests per confirmed case are unlikely to be testing widely enough to find all cases.

"The WHO has suggested around 10- 30 tests per confirmed case as a general benchmark of adequate testing."

READ MORE: Family fear they could have been among the first to bring Covid to Scotland after Italian ski holiday 

At yesterday's press briefing, Ms Sturgeon confirmed that 14 new Covid cases had been identified in Scotland as a result of 2858 NHS lab tests and 558 tests at drive-thru and mobile sites.

There are 15 patients with confirmed or suspected Covid in ICU, down from a peak of 231 on April 12, and a total of 515 confirmed cases in hospital - compared to 1520 on April 19.

Ms Sturgeon said: “Our progress does allow us to consider now whether and to what extent we can give more clarity in terms of indicative dates for the next steps in our routemap out of lockdown.”

She said she will set out more detail on this later in the week. Hairdressers and cinemas are expected to re-open in July but no date has yet been given, and there has been no clear timetable for when relatives can begin visiting loved ones in care homes again.

Phase 2 guidance, revised last week, simply states that "consideration [is] to be given to a phased resumption of visiting to care homes starting with outdoor facilities where it is clinically safe to do so".

Diagnostic tests such as CT scans and endoscopies are to gradually resume, prioritised by clinical need, from Monday.

However, Ms Sturgeon stressed the virus "hasn't gone away" as she pointed to recent outbreaks in Beijing and Germany, where 1331 workers at a meat processing plant in Guetersloh have tested positive. The outbreak has pushed Germany's R number back up to 2.88.

Meanwhile, South Korean health officials say they are battling a "second wave" following a string of clusters linked to nightclubs, office buildings and warehouses. The mayor of Seoul said strict social distancing could be reinstated this week.

“I know that when deaths and cases here are continuing to fall, it’s very tempting for all of us to think it’s all over and we should just quickly get back to normal," said Ms Sturgeon.

"We want to do that as quickly as possible, but let me reiterate my strong view that moving recklessly now would be a serious mistake.”