key: cord-1055386-36udtqc4
authors: Adam, E. J.; Grubnic, S.; Jacob, T. M.; Patel, J. H.; Blanks, R.
title: Re: COVID-19: could CT provide the best population level biomarker? Incidental COVID-19 in major trauma patients suggests higher than predicted rates of infection in London. A reply
date: 2021-03-22
journal: Clin Radiol
DOI: 10.1016/j.crad.2021.03.008
sha: d32c77b1abe7de72027b1f1c35e3acc219ab3b10
doc_id: 1055386
cord_uid: 36udtqc4

nan

Re: COVID-19: could CT provide the best population level biomarker? Incidental COVID-19 in major trauma patients suggests higher than predicted rates of infection in London. A reply Sir-We thank Dr Al Hashmi et al. (1) for their interest in our work (2) . In the UK, all patients sustaining trauma have a single point of entry into the healthcare system.

The study includes all patients (including ambulatory patients) presenting to the major trauma centre who had undergone major trauma and underwent emergency CT, which included the lungs. Our study was unfunded and very difficult to undertake given the time constraints placed on the radiologists by the pandemic. A decision was therefore taken to reduce the workload by using every other month in the control period. The study and control groups had a similar mean age and no adjustment for considered necessary. We included all ages to provide the best approximation to a random sample from the population.

We are unable to provide any further information on the co-morbidities at this point in time other than that they had suffered an accident of sufficient severity to warrant immediate CT, but hope to produce further papers and will consider providing that information in some form going forwards. With regard to Fig. 3 , the points on the dotted line are the percentage of the study group with COVID-19 signs in any 1 week and the solid line (the "green" line as it would be in colour) is the 3-week moving average. The radiologists were blinded to the time period and the graph closely tracks the hospital admissions data (not shown) for COVID-19, but allows us to look at COVID-19 rates in the general population.

Major trauma patients will include all people with no COVID-19, with asymptomatic disease and possibly those with very mild disease who were going about their J o u r n a l P r e -p r o o f normal lives before the trauma event occurred. In none of the cases was COVID-19 suspected by the referring doctor. The percentage of the general population with severe COVID-19 symptoms at any point in time will be relatively small and make no difference to our estimate of population levels of disease. If our results are correct, then it suggests that disease levels are a pyramid with a relatively low proportion of people with severe disease at the top and a very large number of people with asymptomatic or at least unsuspected disease at the bottom. The whole population is exposed but it only "takes hold" and will be fatal in some people, mostly those with specific age-related underlying health conditions and perhaps repeated exposures.

As the disease has no or minimal impact on many people, without testing the whole population the number of asymptomatic or unsuspected cases (who are nevertheless a potential risk to others) has been a universal problem to pinpoint, and a matter of continued debate. We believe the disease swept through the South West London population in February and March 2020 and a significant proportion of the population (up to 50%) were exposed to the disease, with the vast majority being unaware. Our study showed there were many cases of people aged 15-34 years with minor signs of COVID-19 confined to one lung, and it is well recognised that younger people are less severely affected, even when the diagnosis is confirmed.

The London population is younger than average, socially active, and more likely to travel using crowded underground trains or buses, and therefore, in an environment where the disease will spread rapidly. The 17% figure for antibody seropositive prevalence is based on an age stratified representative sample, which corresponds to the same time period and the population who became infected before mid-April, based on the antibody response taking 2 weeks to become detectable.

Our method has advantages over the COVID-19 antibody tests to measure population levels of the disease in that it probably detects all cases, including subjects with just a T-cell response as well as a measurable antibody response; however, our method is not a screening tool at the individual person level, but a method to estimate the disease at the population level. The study only used data that had been collected during the process of examining major trauma patients and did not collect any additional information. The study design therefore does not involve any additional radiation exposure or any additional information to be collected other than the presence of signs of COVID-19. The beauty of the method is that all the data are readily available, and it can be applied anywhere in the world, both retrospectively and prospectively. The method could be further improved, and even, in theory, could be automated and used as an early warning for further waves or in future similar pandemics. It could also be used to look for low levels of disease in the lungs of a vaccinated population, so it has many uses at the epidemiological population level.

Re: COVID-19: could CT provide the best population level biomarker? Incidental COVID-19 in major trauma patients suggests higher than predicted rates of infection in London

COVID 19: could CT scan provide the best population level biomarker? Incidental COVID-19 in major trauma patients suggests higher than predicted rates of infection in London