We have searched through the scientific literature to find out what’s known about contamination of workplaces with the SARS-CoV-2 virus. This is important information for us so that we can compare our measurements with those made by other scientists, and to help us calibrate the model we are building to estimate the risks of infection in different situations.
We found 35 articles that had useful data. These mostly describe measurements made in hospitals with a small number of datasets from public transport settings. The studies were carried out in a diverse group of countries including China, UK, Italy, Spain, USA, Singapore and Iran. The contamination of the air and surfaces were assessed, and in those studies that had data for both it was clear that they were linked, i.e. higher air concentrations were generally associated with higher virus surface loads. We interpret this as suggesting that the surfaces become contaminated by fine droplets from the air.
Typically, around 6% of air and surface samples in hospitals were positive for the SARS-CoV-2 virus, although there was a wide range of results from the different locations. However, most of the studies did not report their results in terms of virus concentrations, which complicates that interpretation of the data. Our best estimate of typical air concentrations in healthcare settings is around 0.01 SARS-CoV-2 virus copies per cubic metre of air. This is low, although in some circumstances the air concentration was more than 10,000 virus copies per cubic metre, and at this concentration a worker might inhale around 100,000 virus particles during a working day.
The standard of reporting in the published studies was poor with it difficult to be sure there was consistency between researchers in the classification of positive samples. There was also little consistency in the measurement methods used. This is a real problem for our understanding of how much virus contamination is present in hospitals and other workplaces. We feel that there should be concerted efforts to standardise the methods used for measuring SARS-CoV-2 and other respiratory viruses in work environments, and that government agencies and the World Health Organisation should take the lead in this initiative.
You can read a full account of our review in a paper we have recently posted on the internet.