The proportion of Covid tests coming back positive in Aylesbury Vale has increased in the last week, and exceeds a maximum threshold set by the World Health Organisation (WHO).
It comes as a drop in cases across England in recent days prompted hope that the current wave of infection has peaked – a trend that ended on Wednesday (28 July).
Positive case numbers in Aylesbury Vale fell by 9.9% amongst people tested in the seven days to 23 July compared to the previous week, from 635 to 572.
But the number of people taking polymerase chain reaction (PCR) tests also fell in the same period, dropping by 12.4% from 7615 to 6670.
Of those tested in Aylesbury Vale in the most recent week, 8.6% had at least one positive result, with duplicate positives for the same people removed.
That is up from 8.2% the week before.
Overall Covid case numbers also include lateral flow tests, whereas the positivity rate counts the more accurate PCR tests only.
Last year WHO recommended that governments should ensure the proportion of coronavirus tests coming back positive remains below 5% for at least two weeks before regions reopen.
The threshold is the maximum limit at which point a pandemic would be considered out of control, although positivity rates would ideally be far lower.
Aylesbury Vale's positivity rate places it 213th-highest out of 315 councils in England.
Across the country, just one council (Somerset West and Taunton) has a rate lower than the threshold, while one (Breckland, in Norfolk) is at 5%.
England’s rate stood at 10.2% in the week to 23 July. That had fallen from 11% the previous week.
The overall number of cases fell by 21.9% in that time, from 289,000 to 226,000. The number of people tested fell by 11.6%, from 2.6 million to 2.3 million.
In the South East the positivity rate is at 8.4% down from 8.8% a week ago.
The highest rate is in the North East (15.2%) followed by Yorkshire and the Humber (13.5%) and the West Midlands (11.8%).
England’s positivity rate has climbed rapidly throughout June and July. In the seven days to 25 June it stood at 4%, rising to 6.1% in the week to 2 July and 7.8% in the week to 9 July.
The rate has fallen since reaching a peak of 11.8% in the seven days to 19 and 20 July, falling for three consecutive days since, although fluctuations in testing on different days of the week can always affect comparisons over periods that are not like for like.
Figures released on Wednesday (28 July) show the number of cases reported in the last 24 hours – regardless of when the test was taken – rose to 27,734, up from 23,511 on Tuesday, and the first daily increase for seven days.
Overall, 87 out of 315 councils saw a rise in their positivity rate in the last week – 65 of which saw a simultaneous drop in recorded cases.
WHO set out its 5% threshold in May last year, long before effective vaccines had been developed and rolled out.
The positivity rate threshold should be used to supplement estimates of the R-number – the rate of the virus’s transmission in communities – to assess whether the epidemic is under control, it said.
In England, 88.2% of adults had received at least one vaccine dose as of 27 July.
WHO has been asked if successful vaccination programmes would affect its guidance on test positivity. It has not yet responded.