BLOG / The idea of “follow” the evolution of an epidemic by analyzing the wastewater of cities is not particularly new. After all, there are already 15 years that we measure the quantities of drugs that a population takes in studying its wastewater, and in a few years we are scrutinizing the genetic material of some viruses. But to “predict” when will the next wave of patients COVID-19 to the hospital ?
This is what a team of Yale University, in the United States, is believed to have carried out by analyzing the wastewater of the city of New Haven (Connecticut), where the university is located. Attention, it is not for the moment, only pre-published, which has not yet been peer-reviewed and whose results should therefore be considered as “preliminary”. But there is something like “the beautiful science” in there (in addition to moving in the same direction as other publications, see here and here), so let’s talk about that a little when even…
The Yale team has sought, it is the genetic material of the COVID-19, which we know is present in the stool of patients — and therefore in the sewage of the city. Between 19 march and 1 may last, the researchers have found between 1700 and 450 000 copies of virus RNA per milliliter of waste water (RNA is a form of genetic material). By “smoothing” the curves to avoid variations too steep will blur the trends, the researchers have obtained a “peak” of about 130 000 / ml to 10 April, followed by a steady decline until the 1st of may.
However, and this is what makes the exercise particularly interesting is that they also compared these concentrations of virus to the number of new confirmed cases and hospitalizations of COVID-19 recorded each day in New Haven. Result : the concentration of viruses in the wastewater prior to the curve of confirmed cases by about a week. In other words, as a pretty good part of COVID-19 are asymptomatic, and that there is an incubation time of several days for all the people affected, the epidemic has become “visible” in the waste water 7 days before of the be in the tests.
In the case of hospitalizations, the “curve of the sewer” was approximately 3 days in advance.
Interestingly, researchers from the Sorbonne, did a similar exercise recently (also in preprint, so, caution). Without curves, which also showed clearly that the wastewater is of advance on the epidemiological indicators in the classics, they have all the same observed that the RNA of the COVID-19 was detectable in the sewers of Paris before the epidemic starts to spread exponentially.
I don’t know if we will ever be able to draw from all this a kind of surveillance system that could have any usefulness in public health, for example by giving a few more days in the hospital to prepare extra beds. It remains to be demonstrated. But with what you have, for the moment, under the eyes, one begins to think : blow, so… maybe…
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