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NHS Test and Trace have released the latest figures for England covering the 9th to 15th of July 2020.
Prof Sheila Bird, Formerly Programme Leader, MRC Biostatistics Unit, University of Cambridge, said:
“In the most recent report-week (9-15 July), 3953 new people tested positive for COVID-19, 872 (22%) of them through Pillar 1, that is: swab testing in Public Health England (PHE) labs and NHS hospitals for those with a clinical need, and health and care workers.
“Around half received their test result within 24 hours; near 88% within 48 hours.
“Around 80% were reached by Test & Trace.
“Around 80% of those reached provided contact information.
“Of 16,742 identified contacts, about 80% were reached by Test & Trace and asked to self-isolate: 13,034 persons, of whom around 5,190 were external close contacts.
“Since 69% of close contact referred to Test & Trace were in the household of the index case (namely around 11,550) and presumably all of them were countable as having been reached and asked to self-isolate – indeed, they should all already have been self-isolating from the time that index case developed symptoms!
“Hence, by subtraction, Test & Trace’s success-rate in reaching the 5,190 identified external close contacts was under 30% (being roughly 1484/5190).
“Multiplying together all four moving parts, Test & Trace hits all four stringent targets for just over a quarter of those who newly tested positive for COVID-19 during 9-15 July.
“The success-rate for Test & Trace rises to 45% if the first target were relaxed from 24 hours to 48 hours.
“For external close contacts, 14-day quarantine begins from the date of their most recent close contact with the index case. Test & Trace’s next task will be to establish for what proportion of the external close contact’s intended 14-day quarantine had already elapsed before s/he was contacted.
“Today also sees the release of three recommendation by the Royal Statistical Society’s COVID-19 Taskforce for remedying gaps in the Test & Trace programme. Use of record-linkage is urged to find out how many of those quarantined by Test & Trace test positive for COVID-19 within or soon after their quarantine period; and of random sampling to find out – during quarantine – about asymptomatic infections and adherence to self-isolation.
“Please see https://rss.org.uk/news-publication/news-publications/2020/general-news/rss-covid-19-task-force-makes-recommendations-for/ and https://rss.org.uk/RSS/media/File-library/Policy/RSS-COVID-19-Task-Force-Statement-on-TTI-final.pdf.”
Prof James Naismith FRS FRSE FMedSci, Director of the Rosalind Franklin Institute, and University of Oxford, said:
“The latest TTI release reports several important pieces of information. The number of people testing positive has risen slightly but appears fairly constant over the last two weeks and has decreased over the last month. The number of tests being performed has risen slightly. The data suggest release of lock down has not led to a general surge in cases as some had predicted. It is too early to declare success, with nearly new 4000 cases a week, the virus is present and as other countries have shown, it can easily take off. There is also a lag time between action and consequence. We have to remain vigilant and be prepared to reverse an action that leads to a surge in cases.
“The report now reports the length of time from presenting for a test to contacts being asked to isolate. Currently 56% of contacts were reached with 24 hours of a positive case being identified. Pushing this percentage up whilst increasing the percentage of pillar 2 notifications within 24 hours (currently 47%) will make a big difference as combined they will shrink the time a person can unknowingly spread the virus. We would like to trace as many contacts possible, the portion of individuals who were reached and reported contacts is around 64%, obviously it would be better if higher.
“Another statistic is that nearly 70% of contacts are within households, consistent with the observation that the virus spreads efficiently in a household. There is still time to plan to support those having to isolate due to a positive test, possibly with free accommodation.
“I remain unclear why we do not automatically test the 13,000 people reached as contacts. It is still a small number and would surely help build public confidence and support especially when coupled to effective isolation of positive cases. It would also help to identify venues or activities where spread occurs more commonly, for example if contacts in the street are commonly negative but contacts in the pub are more commonly positive, then we might introduce targeted measures for pubs and relax a little on rules on outdoors.”
Dr Daniel Lawson, Lecturer in Statistical Science, School of Mathematics, University of Bristol, said:
“Contact tracing is valuable if it is putting people into quarantine that would otherwise gone on to infect other people. The data show that only 30% of contacts traced are with a new household so represent ‘value added’ by contact tracing. Yet this contribution could be important if it cuts onward transmission. The data show that cases continue to drop.
“We know that rapid responses are key to effective contact tracing. The contact tracing time is stable with around 80% of contacts traced within 24 hours. However, the testing speed (proportion of results received within 24 hours) has dropped over the last two weeks. The proportion of people reached by test and trace appears stable at around 80%, and follow-up rates if those contacts are up, though still rather low at 61%.
“For the moment, we are catching enough people soon enough; but we could do a lot better, and may need to if infection rates are seasonal or weather-related, due perhaps to contacts occurring indoors.”
All our previous output on this subject can be seen at this weblink:
www.sciencemediacentre.org/tag/covid-19
Declared interests
Prof Sheila Bird: “SMB is a member of the Royal Statistical Society’s COVID-19 Taskforce which issued today’s Statement and Devil in the Detail Appendix.”
None others received.