Does public transport represent less than 1% of contamination?

The Paris metro in May 2020, shortly after the deconfinement.

(illustration) -

• Is the fear of Covid-19 contamination in public transport exaggerated? 

• Jean-Baptiste Djebbari, Minister Delegate for Transport, said Tuesday on the antenna of BFMTV and RMC that the number of contaminations in buses, trams and subways remained below 1%.

• If we find this figure among different sources, the number of clusters that have appeared in public transport remains very complicated to estimate, as Professor Yves Buisson explains to

  20 Minutes

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  And not all contamination takes place in these clusters.

The closure of bars in Paris and in the suburbs for the next 15 days, intended to fight against the spread of the coronavirus, continues to react.

For many, the fact that the inhabitants of Ile-de-France can continue to use public transport would promote the spread of the virus, despite wearing a mask, especially when social distancing cannot be respected there because of the crowds. , as recent images of crowded metro platforms in Paris have shown.

Two weights, two measures ?

These criticisms were in any case relayed by the journalist Apolline de Malherbe on Tuesday, who did not fail to ask the question to the Minister for Transport, Jean-Baptiste Djebbari, on the antenna of BFMTV and RMC: "Why [ reinforce the restrictions in] restaurants, why [close] bars, and not subways and trams?

"

“Science currently tells us that the most important places of contamination are closed places where people do not wear masks,” replies Jean-Baptiste Djebarri.

“All the scientific studies, which I read every day, tell us that public transport is not a particular place of contamination.

Studies tell us that less than 1% of contamination occurs in public transport.

"

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In France, since the deconfinement of May 11, the clusters observed in transport ("plane, boat, train") have effectively always varied between 0% and a little over 1%, according to data published by Santé Publique France in its report. weekly epidemiological.

Contacted by

, the public establishment confirms that "public transport is included in this type of community" and specifies: "The information concerning the place of occurrence of the cluster is reported via the" contact tracing "work carried out by the '' Health Insurance, regional health agencies and Public Health France teams at regional level.

"

However, as pointed out to

,

Professor Yves Buisson, member of the Academy of Medicine and head of his Covid-19 watch unit, identifying the clusters that have occurred in public transport is proving particularly complicated.

“The definition of a cluster is a focus of infection of at least 3 people within a maximum of 7 days who have frequented the same place.

It is easy to see if three infected people have been in contact when it comes to three students in the same class, or customers of a restaurant, since you can leave your name and address there if necessary. .

But when you have passed a positive person for ten minutes in the metro, the only way to establish this cluster is to use the StopCovid tracking app, ”he explains, while the government It is just hard to convince the French to use this tool.

Clusters far from being the source of all contamination

In addition, clusters are far from encompassing all contamination, continues Professor Yves Buisson: “Clusters only represent less than 10% of all new cases of contamination.

For more than 90% of them, we do not know how or where people got infected.

They say that companies come first, family gatherings ... because we were able to identify them by a survey.

But if someone coughs in the street, and touches you with aerosol spray, when someone asks you what you have been doing for the last ten days, you will quote the metro, the restaurant, etc., but you will not remember that person who has coughed: there is an undetectable risk factor.

"

According to him, the figure put forward by the Minister for Transport must therefore be qualified: "There are not many reference studies on the subject of contamination in public transport, even if we often find this order of magnitude of 1%.

This is a cross-checking hypothesis, a rate that cannot be strictly established with the monitoring means available.

"

A recent study published in the Oxford University Press - and for which the Union of Public Transport and Railways did not fail to relay - showed for example that the risk of transmission of Covid-19 in public transport was rather limited when sanitary measures are observed.

A variable risk depending on the length of the journey

This analysis, based on the journeys of Chinese passengers positive for Covid who took the train between December 2019 and March 2020, explained in particular: “This risk however varies significantly depending on the common duration of transport and the location of the seat.

In times of epidemic, confined transport spaces such as trains must be the subject of measures to reduce the risk of transmission, by increasing the distances between seats, reducing the density of passengers and resorting to measures of hygiene.

"

The researchers' work showed in particular that the risk of contracting Covid-19, for passengers physically close to a sick passenger, was 0.32% - this rate increasing in the event of greater proximity (no row of difference with the sick person) or long contact lasting several hours.

Conversely, a study published in early September showed how an asymptomatic person had infected a third of the occupants of a poorly ventilated coach during a 50-minute journey in China, while none wore a mask.

Hence the importance of the latter in public transport and social distancing in order to reduce the risks of contamination there ("almost zero" in this case with the mask, according to Professor Buisson), even if the first measure does not guarantee total protection when the second cannot be met.

The thorny problem of peak periods

“When users are piled on top of each other, even if they have a mask, the risk becomes greater.

The mask is not a 100% guarantee: it retains most of the droplets and aerosols, but not all.

However, when you are packed against people and a virus carrier is in the middle, if you stay like that for 10 minutes or a quarter of an hour, contamination can happen, this kind of situation is unacceptable during this period. of Covid-19 ”, warns Professor Buisson, who also recommends that users“ not speak and close their mouths ”during their journey to avoid any potential transmission.

On this point, the RATP specifies at

that it is "vigilant as to the load on its lines" while recognizing that "if a certain influx has been observed, it remains very localized and over short time slots ( early in the morning).

"She also recalls that in addition to the regular reminder of barrier gestures on its network and the control of the correct wearing of the mask (mandatory) by its agents," the attendance rate is today 2/3 on the metro networks , RER and tramway and 80% on the bus network compared to a normal period ”with a transport offer at 100%.

The fact remains that, as the president of the RATP, Catherine Guillouard, underlined in April, "respecting social distancing is not feasible in such a dense and already partially saturated network without reducing traffic by at least 80 %.

".

Hence the interest in the increased use of teleworking or the possibility for employees to use transport at staggered hours to avoid crowds.

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