COVID-19: is disinfection over?

What you must remember

A kind of disinfection frenzy has gripped Quebec — and pretty much the entire planet! — at the start of the pandemic, almost 15 months ago. Canadian and Quebec authorities issued recommendations at a time when no one knew exactly how the COVID-19 virus was spreading. That's why we've gotten into the habit of cleaning door handles and power switches with disinfectant, even if we don't let anyone in.

On social networks, some admit to being in a hurry to get rid of all these new cleanliness rituals, which take time and money, while others would feel calmer if they were kept. Since scientific knowledge has evolved a lot over the past few months, we surveyed experts to determine which actions are no longer necessary, and which should continue.

Lower and lower risks

From the summer of 2020, it became clear that the mode of contamination by contact with surfaces was incidental, compared to the risk of transmission by droplets of saliva and aerosols projected by carriers of the virus. Epidemiological investigations have found very few cases where objects, such as a door handle or an elevator button, could have explained the infection of certain people. And even if it had happened, it would have been impossible to prove it. Contamination by surfaces was still described as "possible", and the authorities preferred not to revise their instructions, despite the fact that some seemed less and less justified.

In Quebec, for example, we continue to recommend increased cleaning of the interior of homes… even if it is only visited by the people who live there. “It is of very little use to limit contamination between members of the same household, who share the same air and touch each other. If I hug my children, cleaning the remote is useless! explains Christian Jacob, president of the Association of Microbiologists of Quebec.

On its site, the Public Health Agency of Canada recommends cleaning and disinfecting “your home each time a person returns after having had close contact with other people or frequently touched surfaces”. While the majority of people have probably understood that with masks and distancing, all you have to do is wash your hands when you return from the grocery store or school, the fact remains that this extreme instruction is enough to stress the more anxious.

The Standards, Equity, Health and Safety Commission (CNESST) indicates, for example, that meal areas must be cleaned after each use and disinfected daily, but without specifying when. In several places, this disinfection of common areas is done at the end of the day. However, as Christian Jacob points out, disinfecting a place where no one will go for several hours is useless, because time also does its work to remove all traces of infectious viruses. The risk of being contaminated by eating your lunch on a table that has not been used since the day before is absolutely negligible.

Clean rather than disinfect

In April 2021, the US Centers for Disease Control and Prevention (CDC) for the first time rated the risk of surface transmission as "low", rather than "possible". In Quebec, the National Institute of Public Health of Quebec (INSPQ) will publish its new recommendations on the subject within two weeks, says ^Dr. Caroline Huot, medical advisor at the INSPQ. This notice will be used by the Ministry of Health and Social Services (MSSS), which may modify the instructions to the population accordingly, while the CNESST may do the same with businesses. “We are going to report on this notion of low risk, even if other authorities have not yet taken this step. We are also going to modify the recommendations on disinfection, which will no longer be recommended for each cleaning as it was before, ”explains Caroline Huot. Already, several northern European countries, such as Finland and the Netherlands, no longer advocate disinfection since this winter.

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Even for frequently touched surfaces, the INSPQ will indicate that cleaning once a day with an ordinary detergent such as soap, and not with a disinfectant, is sufficient, because it eliminates at least 90% of the traces of virus which could subsist. “We should just disinfect the rooms where people carrying the virus or suspected of being infected have stayed”, specifies the doctor.

The MSSS and the CNESST will therefore have to review their instructions accordingly, recommending not to use disinfectants where they are not necessary. “These are not products that should be used lightly, since they are often respiratory irritants for the people who apply them,” warns Christian Jacob. Although alcohol is far less toxic than products containing chlorine or acetone, breathing vapors in a poorly ventilated area isn't ideal either.

But as the virus gradually becomes less present in our environment, is there still room for increased cleaning? Some of the previous instructions already took into account that the virus was circulating more or less. For example, disinfection of frequently touched surfaces in school buses was recommended only in red or orange zones. We do not know for the moment what the CNESST and the MSSS will recommend in this new context.

What we should keep, what we should let go

Knowing this, what should we continue to do? The priority, according to Christian Jacob and Caroline Huot, should be washing hands, which remains relevant since they are frequently worn on the face, near the respiratory system, where they are likely to bring the virus, whether it is transmitted by droplets, aerosols or objects.

The two experts thus think that we should, for example, for the moment, keep hand washing at the entrance to shops and public places.

Disinfect grocery baskets before each customer? Yes, according to Christian Jacob, because our hands still remain on the handles for a long time, and these businesses see a lot of people passing through. ^Dr. Caroline Huot, she believes that cleaning once a day would now be sufficient.

Objects that you touch little with your hands, such as chairs in a waiting room, pose even less of a risk, and the two specialists believe that there is probably no need to clean them after each use.

Certain rules introduced to protect employees and certain cleaning chores should also be revised, according to Christian Jacob. Refuse to fill a reusable cup or lend a replacement vehicle? Nope !

Risks of overdoing it?

Like many microbiologists, Christian Jacob believes that it would be in our interest to keep certain good hygiene and sanitation habits taken during the pandemic. Stay home when you are sick. Wear a mask when you have symptoms of respiratory illness. Wash hands after touching surfaces or objects that many people have touched.

However, does increased sanitization of our environment risk playing tricks on us? In January, a group of 23 researchers published a warning about the effects on the human microbiome of the measures adopted against COVID in the journal PNAS. Without criticizing the rules necessary to control the pandemic, they worry that they may in the long run affect the human microbiome: a more sanitized environment, less contact with other people and less travel impoverishes microbial biodiversity than we encounter daily. This could have consequences for the microbes with which we live in symbiosis and, in turn, for our own health, say the researchers. They are reminiscent of the hygiene hypothesis, a phenomenon that is believed to explain why ailments such as asthma, food allergies and certain autoimmune diseases have increased in recent decades in industrialized countries, where we live in a more sanitized environment than in poor countries.

"The idea that increased sanitization during the pandemic could have an effect is an interesting hypothesis, but it will have to be verified," said ^Dr. Philippe Bégin, allergist at Sainte-Justine Hospital. “We will see in a few years if we see a resurgence of asthma or allergies in children. The doctor is not worried, however, as he doubts that a more sanitized environment for just over a year will have any long-term consequences.

In any case, these assumptions do not justify stopping protecting against pathogenic microbes like SARS-CoV-2 while they are still present in our environment: we do not need dangerous microbes to have a good immune system! However, we must keep in mind that disinfecting places or objects, when it is no longer necessary to protect us against pathogens, could also deprive us of "good" microbes and prove to be counterproductive.