Estimates of Hidden COVID-19, Seattle and Wuhan, January-March 2020: Lancet EClinicalMedicine

This study came out online in Lancet on August 13. It used swabs tested previously for influenza in a surveillance study in the Seattle area early this year. Of 2353 patients tested between February 24 and March 9, 442 were positive for influenza and 25 were positive for SARS-COV-2. A complex analysis led to an estimate of 6635 COVID-19 cases in Seattle for that period. With these methods, the authors were able to estimate that the pandemic started with an introduction to the Seattle area between December 25, 2019 and January 15, 2020 by someone probably infected in Wuhan.

This timing corresponds with another study that found a patient in Europe infected by the novel coronavirus on December 25, 2019, who was retrospectively identified this spring from a stored specimen. His source of infection, unfortunately, remains unknown, but the virus spread to his entire family. [Sorry, I can’t find the reference for that study.]

Clearly, this estimate of 6635 cases is vastly more than the reported number of patients with COVID-19 for that area at that time: a total of 245 confirmed cases were reported before the town was locked down on March 9. It is not that the authorities missed all those cases, just that they were unable to even look for them with the limitations that hindered public health surveillance at that time (some of these hindrances persist to this day.)

In Wuhan, a similar situation held, and the paper estimates that, while 571 patients were officially counted, roughly 15,000 cases of COVID-19 occurred between December 30, 2019 and January 12, 2020. The vast majority of these cases were missed, due to similar limitations of awareness and testing ability. The authors estimated that the infection began with one or a few cases between October 26 and December 13, 2019.

The implication (supported by genetic testing of the virus) is that the jump from animal to humans occurred in October 2019. The exact location of the jump or the species that contributed to this zoonotic spread is still unknown. Bats have been blamed as the original source with considerable evidence, but some scientists believe that an intermediate species was involved.

The article’s “Interpretation” states that:

The spread of COVID-19 in Wuhan and Seattle was far more extensive than initially reported. The virus likely spread for months in Wuhan before the lockdown. Given that COVID-19 appears to be overwhelmingly mild in children, our high estimate for symptomatic pediatric cases in Seattle suggests that there may have been thousands more mild cases at the time.

https://www.thelancet.com/journals/eclinm/article/PIIS2589-5370(20)30223-6/fulltext#seccesectitle0009

This means that, with the benefit of hindsight, we can see the onset of the novel coronavirus and its hidden spread through the community among undetected patients. The virus is far more widespread than initially thought, and many of its victims are asymptomatic or are thought to have the much more common influenza– which has very similar symptoms, although it is less than half as lethal.

A big difference between COVID-19 and influenza is the fact that the novel coronavirus spreads to the blood vessel walls, the heart, the brain, and other organs as well as the lungs– and leads to blood clots, neovascularization, strokes, and myocarditis (inflammation of the heart muscle.) These things very rarely happen with influenza.

The authors suggest that the analytic technique they used to estimate the prevalence of the novel coronavirus could help assess other novel virus epidemics earlier than has currently been possible. A high index of suspicion is essential to detection of new viruses. Caution and good hygiene are also important when dealing with unknown respiratory infections.

Perhaps the Asian habit of wearing masks in public during flu season should be made fashionable in the US. Universal immunization against influenza and with the new coronavirus vaccination, when it is available, should be on our agendas as well.