A study, published by eLife, reports on screening healthcare workers for COVID-19.
Prof Ashley Woodcock, Professor of Respiratory Medicine at the University of Manchester, said:
“This is high quality research. Levels of asymptomatic carriage are likely even higher in high exposure NHS workers.
“This work has major implications in addressing transmission in these settings. In hospitals this virus is contracted from patients by droplet spread with prevention by visors rather than facemasks. But healthcare workers could also be cross-infecting through contact with infected surfaces”
“We should work on the basis that there is a high level of asymptomatic carriage and presume that anyone we encounter in the community could be carrying the virus”.
“We know that this virus can persist for days on surfaces and can be passed on by surface contact so personal attention to hygiene and cleaning will help to control spread. It is not an airborne live virus in the community so facemasks are of little use.”
Dr Robert Shorten, Chair, Microbiology Professional Committee, Association for Clinical Biochemistry and Laboratory Medicine, said:
“It is clear that some transmission of infection occurs from people when they are asymptomatic or pre-symptomatic (i.e. carrying the virus, but they don’t feel unwell yet). Mass testing of asymptomatic people may detect some of these cases. However, the molecular tests for SARS-CoV-2 were never designed as screening tools in well people and this approach creates some issues. To examine this, we need to consider the terms sensitivity and specificity. Sensitivity is a measure of how certain we are that we can believe a negative result. If a test is 99% sensitive, then if we test 100 patients with a disease, the test will detect 99 of them. The remaining one is a false negative. Specificity is a measure of how certain we are that we can believe a positive result. If a test is 99% specific and we test 100 patients without a disease, the test will give a negative result 99 times out of 100. The remaining one is a false positive. Even if a test has a seemingly high sensitivity and specificity, this is no guarantee of performance. This is particularly true when the prevalence of a disease is low, and we have no firm grasp on the true prevalence of COVID-19 in the UK population. Issuing false negative and false positive results will lead to inappropriate public health actions. No diagnostic test is 100% sensitive and specific, and we need to be aware of, and take into account these limitations.”
Prof Jonathan Ball, Professor of Molecular Virology, University of Nottingham, said:
“This perfectly highlights how important aggressive testing can be in identifying, and therefore controlling, coronavirus spread. The study also highlights the benefits of routine testing of healthcare workers as these people are most at risk of becoming infected and can also be potential sources for hospital outbreaks. Controlling coronavirus spread in this setting will be important if the NHS and our hospitals are going to get back to offering important healthcare.”
Dr Joshua Moon, Research Fellow in Sustainability Research Methods in the Science Policy Research Unit (SPRU) at the University of Sussex Business School, said:
“Although the sample size is a little low to be banking on the 3% number being precise, this study does highlight the importance of solving an open question of whether asymptomatic carriers can transmit the virus to others.
“On top of this, it highlights limitations in a strategy which focuses in on testing only those who are symptomatic, as it is likely to miss asymptomatic carriers which (if they can transmit the virus) would be a significant source of infection.
“Overall, this study highlights just how much we still do not know about this virus and how to effectively respond.”
Prof Sheila Bird, Formerly Programme Leader, MRC Biostatistics Unit, University of Cambridge, said:
“This is an excellent study from Addenbrookes Hospital with important results; 7/454 (1.5%) screened asymptomatic healthcare workers in green locations were swab-test positive versus 24/544 (4.4%) who worked in amber/red zones (p < 0.01).
“Two wards were focused on, respectively because of unusually high staff sickness rates (ward F, green zone) and concern about appropriate PPE usage (ward Q, red zone). The surveillance results validated both prior concerns.”
Prof Daniel Altmann, Professor of Immunology, Imperial College London, said:
“In our clamour for more and more testing, its easy to forget why we really need it in the population and how it can help us. This paper is a snapshot of 1000 healthcare workers screened over a 3-week period at Addenbrookes Hospital, and really shows the real-life value and importance of the data. Most of all, it enables them to make the really key point that focus on testing symptomatic cases poses an actual risk of missing the significant spread of infection by people who have no clue they’re infected. This has such enormous implications for how we move forward in our hospitals and care homes.”
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Prof Bird is a visiting senior fellow at the University of Cambridge but was not involved in this study.
None others received.