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The MRC Centre for Global Infectious Disease Analysis has released a new report on the sensitivity of international surveillance estimating how many cases exported from mainland China might remain undetected.
Dr Thomas House, Reader in Mathematical Statistics, University of Manchester, said:
“This report is presents work of the kind that modellers would often call a ‘back of the envelope’ calculation – this means that it makes very clearly stated assumptions about how cases have been exported from China and does not require large amounts of computer time to run, but at the same time does not attempt to represent full epidemiological reality. It is possible that COVID-19 has some currently unknown features that make the simplifying assumptions invalid, but there is no evidence that this is the case as yet. Therefore the study does provide quite strong indirect evidence that a large amount of international spread has gone undetected, which recent events seem to confirm more directly.”
Comments sent on Friday 21 February:
Prof Richard Tedder, Professor of Medical Virology, said:
“The fact that so many potential infections are not being recognised is one of the principal reasons that a number of organisations feel that antibody testing should be developed and should be developed soon. The clinical symptoms in the majority of people who are not seriously adversely affected by SARS CoV 2 are so non-specific that it really is not possible to construct a sensible case definition for epidemiological purposes. In light of this the development of a serological test for evidence of past infection is urgently needed in order to give a more expanded numerical database of infected persons.”
Prof Rowland Kao, Sir Timothy O’Shea Chair in Veterinary Epidemiology and Data Science, Royal (Dick) School of Veterinary Studies and Roslin Institute, University of Edinburgh, said:
“In this analysis the authors assume that travellers leaving China would have the same risk profile no matter where they are travelling to. If this is reasonable, and if the true number of cases is proportionate to the number of reported cases, then by comparing the volume of traffic for each destination country, it should be possible to estimate the amount of under-reporting by comparing observed cases to the country which reports the highest rate of cases per traveller (in this case Singapore). This is a sensible first assumption to make and the analytical methods used appear robust (no less would be expected from this highly respected group of scientists). This analysis could provide valuable insight into where further surveillance or more intensive controls may be required.
“Further investigation into the nature of activities being conducted could uncover some variation in risk. For example, tourists may have a different risk profile to business travellers as the nature and location of contacts they have with local inhabitants may be quite different. Package holiday tourists may also have a different risk compared to backpackers. Older travellers may present a different profile compared to younger ones, and similarly affluence may play a role. If these profiles are evenly spread across countries, then the result is likely to be robust. However if there are substantial biases in the types of traveller by country, this could potentially influence the analysis.
“Another factor is that air travel itself is a risk of transmission and some cases may have occurred on the airplanes themselves. Thus the size of the airplane, how crowded the passengers are, and in particular the duration of travel may have an influence on the expected number of cases.
“Unfortunately it would be difficult to tell without further investigation and knowledge of transmission whether these factors increase or decrease the likelihood of under-reporting. In particular it would be useful to know whether Singapore, the country used as the point of comparison, have travellers who are higher or lower risk than average.”
Prof Jonathan Ball, Professor of Molecular Virology, University of Nottingham, said:
“Given the large number of cases reported in China, and suspected unseen community-transmission of the novel coronavirus there and elsewhere, we should not be surprised that this report suggests that this virus is more widespread than official figures suggest.
“With each new finding of how this virus is behaving – large proportions of people with mild or no symptoms, frequent detection of the virus in the nose and throat irrespective of disease severity – we should start to accept that this outbreak will be incredibly difficult to control using standard public health measures, such as isolation of cases and contact tracing.
“Whilst case numbers in the UK and other places with good surveillance and strong public health systems is still low, it is very likely that the virus is spreading undetected in other parts of the world. It might also be true even for those places with good surveillance as these systems are focussing on specific risk groups.
“I don’t think too many people would argue that we are likely to see continued spread around the world and the eventual emergence of what will be the fifth commonly circulating human coronavirus infection.”
https://www.imperial.ac.uk/mrc-global-infectious-disease-analysis/news–wuhan-coronavirus/
All our previous output on this subject can be seen at this weblink:
http://www.sciencemediacentre.org/tag/covid-19
The SMC also produced a Factsheet on COVID-19 which is available here:
https://www.sciencemediacentre.org/smc-novel-coronavirus-factsheet/
Declared interests
None received.