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Covid-19: Why it’s best to go to the supermarket in the early morning


“Ventilation is more important than a mask (which remains a necessity) to stop the spread, but there is no attention whatsoever given to that.”

GOOD ventilation can be more important than wearing a mask (which remains a necessity) to stop the spread of the coronavirus, but there is no attention whatsoever given to that, says an epidemiologist.

Wearing a mask when you go to the supermarket, for example, might not be enough to protect you against contracting the coronavirus – if you go later in the day.

Epidemiologist Dr Jo Barnes, from the University of Stellenbosch, told Independent Media: “If you go to the supermarket, please try to go in the early morning. They have shown overseas that there are a lot of people spending time inside the supermarket before moving out and if that air hasn’t been properly filtered or ’scrubbed’, it does really build up over the day with a high viral load.

“The viral load in the air goes up and the mask can’t cut out 100% of the viruses. The higher the ventilation challenge, the more likely you are to breathe in some of the contaminated air. The mask is not only there to protect you from the air you breathe in, but also what you breathe out.’’

Air-conditioning systems form a major part of pandemic safety measures, playing a major role in the cleanliness and circulation of air, and an even bigger role in minimising the spread and survival of airborne viruses, both in the air and on surfaces.

The Centers for Disease Control and Prevention in the US says: “SARS-CoV-2 viral particles spread between people more readily indoors than outdoors. Indoors, the concentration of viral particles is often higher than outdoors, where even a light wind can rapidly reduce concentrations.”

A recent study conducted by investigators from the University of Central Florida has found that good ventilation and masks are significantly more important in reducing the airborne spread of Covid-19 than social distancing.

“When indoors, ventilation mitigation strategies can help reduce viral particle concentration. The lower the concentration, the less likely viral particles can be inhaled into the lungs (potentially lowering the inhaled dose); contact eyes, nose and mouth; or fall out of the air to accumulate on surfaces.

“Protective ventilation practices and interventions can reduce the airborne concentrations and reduce the overall viral dose to occupants,’’ the study said.

Barnes said: “One in three people get Covid-19 without any symptoms so they think they only have a cold, but during that time they still breathe out viruses. It’s a crisis that so many people are asymptomatic and unaware that they can pass on the virus.’’

In First World countries, this is a pubic health and safety issue at buildings that are being inspected on a regular basis. But there has often been no planning, extra care taken or awareness created when it comes to ventilation in public buildings, shops, malls and office buildings in South Africa, Barnes said.

“Nobody is even planning to go and inspect to see whether those ventilation filters have been cleaned and whether it still works. Ventilation is more important than a mask (which remains a necessity) to stop the spread, but there is no attention whatsoever given to that, which I find worrisome.

“This is not a Department of Health thing but the responsibility of the local municipal authority and part of building safety inspections and so on. That for me is a glaring omission.

“You need to test to ensure that your ventilation system is up for the task. You will be horrified to see some of those clogged filters that come out of the ventilators of some of these public buildings.

“If you are an events co-ordinator, please ask what the state of the ventilation is. Businesses don’t want to suck in so much outside air because then they have to either cool it or warm it and that costs a lot more money. So they are actually trying to save lot of money by having a primitive and poorly functioning ventilation system.’’

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