COVID 19 – The Widow of Hampstead Revisited
April 27, 2020
Tom Jefferson, Carl Heneghan
We have previously pointed out the importance of careful examination of any outliers in the distribution of cases or deaths in an epidemic curve.
The events of February 2020 in two epicentres, Codogno in the province of Lodi in Lombardy and Vò Euganeo in Padova in Veneto region may shed some light on the dynamics of viral transmission.
The two centres are 230 km apart, both situated in the Eastern (Vò) and Central (Codogno) sections of the Po Valley of Italy. The two villages have very different size, habitation density and infrastructure.
Vò has some 3,600 inhabitants and is a village on a predominantly low hilly part of the region. Codogno has just under 16,000 inhabitants and is part of a light industry belt with an important slaughterhouse nearby. The land around Codogno is as flat as a pancake.
Early reports suggested the synchronous appearance of autochthonous (with no apparent link) cases of COVID-19 on the 20th February.
Thereafter the epidemic accelerated at a very fast rate in some provinces of Lombardy but far slower in the Padova province of Veneto, as the figure shows.
See COVID 19 cases by province by week starting 23 February
In the days between the 20th and the 25th of February, Lombardy went from 1 case to 560 cases, an increase of over 500 fold, with the province of Lodi leading the way (125 cases).
No wonder the health services were overwhelmed. After an explosive start, the province of Padova had a “modest” 27 cases out of 29 cases for the whole of Veneto by the 24th of February. There was an apparent slowing down of the spread after containment measures were put into place on the 24th.
The Lodi province curve is unlike the curves in other provinces of Lombardy with an almost straight oblique trajectory. Deaths in the whole Lombardy region escalated soon afterwards with the highest daily increase (73%) on the 8th March, the day that nearly 70% of the swabs taken were positive for COVID-19.
What happened in Codogno and in the wider province of Lodi is still unexplained, despite the alleged index case having survived. To our knowledge, it is a unique event in the history of the pandemic. We cannot entirely discount the effects of ascertainment bias, when the media were alerted to the presence of autochthonous cases and triggered interest and perhaps reporting. Reliable eye-witnesses are not convinced by this explanation and the tight time frame would not fit this explanation.
There were two remarkable events.
The first is the synchronicity of appearance of the index cases with no apparent contact with one another. The second is the speed of viral transmission within Codogno and its environs.
Synchronicity was noted in the Spanish influenza story by expert eye-witness accounts and again in the influenza epidemic of 1932-33. It formed the basis of the work of a humble GP in Cirencester, Edgar Hope-Simpson, arguably one of the greatest thinkers on influenza and other respiratory virus epidemiology. Although ascertainment bias could play a part in the reporting of synchronous foci, we think this is unlikely here as in February everyone was caught by surprise by their appearance.
The only other explanation we can think of is the unrecognised presence of COVID-19 in most of the affected areas for a longer period than hitherto recognised and its sudden activation by environmental factors such as low humidity, mild temperatures and low UV light, all of which could be context-dependent but were present in both Codogno and Vò Euganeo for a period preceding the outbreak. This would explain the north to the south gradient of cases and deaths in Italy and the differential in global mortality with increasing latitude.
The fast speed of transmission could again be explained by environmental factors or another hitherto unrecognised variable. Agents other than COVID-19 may have played a part.
In 1918 some celebrated autochthonous mortality hotspots such as Western Samoa and Lapland had cultural and environmental co-factors. This may be true in Northern Italy. If that is so, contemporary events and history indicate the peril of generalising across contexts and simplifying causation and spread models.
The origin and spread of the pandemic are also far from clear, but the repeated reporting of multiple synchronous foci should be investigated in today’s pandemic. This may give us an indication of the means of seeding, trigger, and possible spread of respiratory viruses.
Either way, such hypotheses should be urgently examined and accepted or discarded, as they are not an academic ivory tower point.
The same environmental conditions could be present next winter or the winter after, possibly re-igniting transmission. This time, we should be ready with well-stocked dedicated infectious disease self-standing facilities as history has taught us to do.
Effect of Latitude on COVID-19
COVID-19 deaths compared with “Swine Flu”
Six countries: Three-quarters of the COVID Deaths
COVID-19 Global Charts of Deaths
COVID-19 – Is Lombardy the Widow of Hampstead?
Tom Jefferson is a senior associate tutor and honorary research fellow, Centre for Evidence-Based Medicine, University of Oxford. Disclosure statement is here
Carl Heneghan is Professor of Evidence-Based Medicine, Director of the Centre for Evidence-Based Medicine and Director of Studies for the Evidence-Based Health Care Programme. (Full bio and disclosure statement here)
Disclaimer: the article has not been peer-reviewed; it should not replace individual clinical judgement and the sources cited should be checked. The views expressed in this commentary represent the views of the authors and not necessarily those of the host institution, the