When Did the Epidemic Start and How Widespread Has it Been?

By April 15, 2020 Commentary

The evidence is mounting that the current strain of coronavirus was circulating earlier and more widely than has been accepted, leading to a higher percent of the population having been infected.  It is maddening that enough testing supplies have not been available to do any significant random sampling of the population for either infections or antibodies.   (Medrxiv Paper)   The researchers used a database of primary care medical records covering over 6 million patients in Spain.  They compared trends for the flu seasons from 2011 to the current one. Four of the seasons had a profile similar to the earlier months of the current flu season, so those years were used to compare influenza cases to this season.  The peak of the flu season occurred on February 4.  The downward curve began to depart from the usual pattern about two to three weeks later and the departure can be seen visually on a chart, as well as by the mathematical calculations.

The researchers concluded that around 8000 “excess” influenza cases were diagnosed from February 4, 2020, to March 20. Most cases of suspected influenza are not tested because it would not change how the patient is treated for most patients.  The researchers believe that a number of the excess influenza cases were likely coronavirus disease.  This is supported by the fact that the excess flu cases began to decline as coronavirus testing ramped up.  It is also likely that the introduction of mitigation of spread measures affected the incidence of influenza.  The presence of the likely coronavirus cases meant that community transmission to a large number of individuals was likely occurring well before the presence of the epidemic was recognized.

A similar finding was reported in the Journal of the American Medical Association in a research letter.  (JAMA Letter) The authors studied swabs taken from patients suspected of having influenza and also tested those swabs for coronavirus.  They found that out of 131 samples, 7 were positive for coronavirus.  They also reported that across the US, the influenza sentinel system had an unusual third spike late in the season while at the same time influenza test positive results were going down.  This also suggests that coronavirus was spreading early than was believed in the US and that a higher percent of the population than models use has been infected.

Leave a Reply