Coronastream: don’t you know it’s Christmas, Covid?
Posted on December 21, 2020 by Dr Tim Inglis
In this special blog series, medical microbiologists led by Dr Tim Inglis summarise some of the research that will be essential to inform COVID-19 countermeasures. Find out more about the project in Dr Inglis' Editorial 'Logic in the time of coronavirus', published in the Journal of Medical Microbiology.
As we edge towards the end of a year that has tested the limits of human endurance, and taken testing well past its limits, the misguided idea that we're getting closer to the end of the pandemic has begun to corrode our resolve to see off SARS-CoV-2. Recent announcements about early vaccine successes, and the first mass vaccination programme are grounds for incautious optimism that this may all be over by Christmas. But, just like the Great War, it won't end in time for Christmas 2020. In fact, it is more likely that overly optimistic expectations will combine with the seasonal excess to trigger another round of virus transmission in time for mid-January. If we have to go in for blame-laying, let's remember that it was the virus that stole Christmas and all the other things we've missed out on this year past.
Congruence: clinico-pathological features
We have learned much about the importance of timely, accurate laboratory tests through the COVID-19 pandemic. The public health authorities that use this data to drive their operational decision-making have favoured measures of sensitivity over all else, forcing clinical laboratory services to rely on nucleic acid amplification tests, which have exquisite sensitivity, but lack practicality in a pre-hospital setting and do not necessarily indicate infectivity. This paper references statistical modelling that demonstrates how a lower sensitivity laboratory test that can be repeated on several consecutive occasions has a higher cumulative sensitivity than a highly sensitive test performed only once on asymptomatic subjects who may be in the potential pre-symptomatic period. This more pragmatic way of thinking, through the use of SARS-CoV-2 tests to support public health decisions, clears the way to a COVID-19 test algorithm that uses one or more of the emerging SARS-CoV-2 test modalities to triage subjects for more selective, reflect nucleic acid amplification tests.
This Cochrane review concludes that at the time of writing the evidence was not strong enough to know whether the tests reviewed would work in practice either to select for PCR assay, or to use instead of PCR.
Case-Control Study of Use of Personal Protective Measures and Risk for SARS-CoV 2 Infection, Thailand
he controversy over whether facemasks protect against COVID-19 or not persists in some quarters, despite recent studies that should settle the issue. This study from Thailand used a case-control design to address the effect of mask wearing on infection. They recruited 211 people with COVID-19, defined symptomatic contacts of COVID-19 who later returned a positive test for SARS-CoV-2. The 839 people in the control group were asymptomatic and did not return a positive test. Wearing masks all the time during contact was associated with a lower risk of SARS-CoV-2 infection, when compared with not wearing masks. Interestingly, wearing a mask occasionally during contact periods did not lead to a lower risk of infection, and the type of mask was not independently associated with infection. Other findings from this study were that maintenance of a social distance of more than one meter, keeping close contact to less than 15 minutes and frequent handwashing were also independent predictors of lower infection risk. While there may be theoretic confounding variables in this study, such as combined benefits of multiple hygiene measures, the overall conclusion is that personal protective measures will modify the epidemiology of COVID-19 if they are properly and consistently practiced.
Cumulative dissonance: pathophysiology
In this observational study of intensive care patients with severe COVID-19, Sirivongrangson and colleagues investigated the underlying cause of clinical features of sepsis. They investigated the possibility that these patients experience a breakdown of epithelial barriers allowing ingress of bacterial components that lead to the notable overlap between severe COVID-19 and bacteria-caused sepsis. While they recorded a positive blood culture in only one of the patients studied, 18 of 19 had bacterial DNA in their blood, most commonly of proteobacterial origin. Other moieties of bacterial original were also detected. Endotoxin was also detected at high level in some of these patients. These findings put a different complexion on the role of bacteria in severe COVID.
The perspective of fluid flow behaviour of respiratory droplets and aerosols through the facemasks in context of SARS-CoV-2
Wearing of facemasks has become commonplace wherever COVID-19 is highly prevalent. There has been much discussion around whether facemasks are effective, their optimal composition and use. Some of that discussion has been heavy on opinion and light on science. This helpful paper by Kumar and Lee provides a detailed review of the science behind fluid flow, aerosol protection and facemask efficacy. While the fluid dynamic aspects of facemask use are complex, this paper illustrates and explains phenomena that have a practical bearing on facemask selection, training, application and use. The figures illustrate the difference between mechanical filtration and electrostatic filtration, the wide variation of filter efficiency between masks of different materials, and the performance difference between medical and cotton facemasks. Thermal comfort, flow resistance and viral filtration efficacy are all discussed.
COVID resource of the month
For those who are struggling with the COVID-19 anxiety or depression, the Black Dog Institute have given us some tools to help us through.
Image of the month
This recent feature from the BBC usefully summarises the key features of some of the leading SARS-CoV-2 vaccine candidates in the news recently.
The Grinch's corner - for those who need a specifically seasonal angle on the pandemic.