BAD BODY – The potential of monitoring the virus at wastewater treatment plants has been proven in previous waves. In Paris and Marseille in particular, the latest readings are of concern.
– Interview by A. LE GUELLEC
Do the sewage pipes already contain evidence of the dreaded acceleration of the post-holiday epidemic? Since the appearance of Covid-19 in China, the hunt for the virus in wastewater treatment plants has presented itself as a formidable weapon to the point that several regions have adopted a predictive surveillance strategy in recent months. It turns out that the latest readings made in Paris and Marseille attest to an increase in the concentration of the virus not really auspicious.
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What to fear and when? Is there any reason to believe in a false alarm in light of the experience of the past few months? What about the impact of the English variant on the bad data collected? Vincent Maréchal, virologist at the Saint-Antoine Scientific Research Center in Paris and member of the Obépine network, a research consortium which notably associates Sorbonne University, the University of Nancy and the Biomedical Institute of the Armed Forces, helps us to see more clearly.
The presence of the virus in wastewater is an early indicator that must be crossed with other– Vincent Maréchal
LCI :What do the latest readings show?
Vincent Marshal : We were all a little worried when we saw the latest readings in certain regions, in particular in Ile-de-France where the circulation of the virus is increasing in the five stations of the Obépine network. That is to say, since January 4, we have seen an upward recovery which is registered at least on two consecutive withdrawals. What we are seeing is more people secreting the virus than a week ago and this is the first time that this has happened since the end of October. Is it an epiphenomenon or something lasting? It is too early to tell and we hope to be wrong in sounding the alarm, but there is little chance that it will not be lasting. We are analyzing the data station by station because several parameters must be taken into account such as the number of infected people, the size of the population, any work in progress, heavy rains which could have diluted the concentration of the virus. .
But one thing is certain, this upward recovery reflects a change in momentum when we were on an already relatively high plateau, with figures similar to those of mid-September. In my opinion, if the recovery is confirmed, it is therefore difficult to speak of the third wave, because we never really got out of the second.
After several months of using this method, are there any reasons to believe in a false alarm?
The big advantage of this indicator is that it is not biased. To simplify, as soon as people go to the toilet we know what it is about the circulation because even if the disease has a respiratory expression, it replicates in the digestive tract and this is what we are looking for in stool present in wastewater. All summer, for example, we have seen quantities of viral genomes go back up to October, then the quantities decrease and register in a plateau. This very slow ascent heralded a catastrophe that had taken place. However, it is difficult to say that what we learned from a phase will be repeated, because the measures evolve and the epidemiological context too. The predictive nature and the anticipation period are not absolute.
The presence of the virus in wastewater is an early indicator that must be compared with other indicators. Unlike this summer when the recovery was observed initially among young people in seaside resorts and a meteorological context less favorable to the circulation of the virus, we can predict that this time, the population concerned is not the same. , in an urban context and a meteorological situation very favorable to the circulation of the virus. As a reminder, at the time, the first lifts were detected on June 20 and the indicators had started to panic at the end of July. We therefore have every reason to be concerned when seeing these latest readings. And we did not need, in addition, a variant of the virus to be added to that.
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Exactly, what about the detection of the variant in wastewater?
We are not able to say for the moment whether this observed increase is linked to the “classic” virus or to the variant because the method we had chosen until then aimed precisely at detecting all the genomes so that no variant escapes us and that the detection of the virus circulation is as comprehensive as possible. But now that the situation has changed, we are working to target variants, and in particular this one. We are currently evaluating its prevalence using tools to specifically detect it and assess its proportion in circulation.
Interview by A. LE GUELLEC
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