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Coronavirus in the air: Why social distancing matters

Covid-19 coronavirus (like all flus) can spread in many ways. Hand washing is important, but few people know about the aerosolised (airborne) version of Covid-19.

This deadly virus (like all flu viruses before it) can be transmitted from an infectious person through pulmonary (lung-based) events like sneezing, coughing, singing and talking. These events emit aerosols and droplets and our face (nose, mouth and eyes) as well as clothes and nearby objects are contaminated as a result. Let us try to understand the various mechanisms of airborne transmission.

First, let’s talk about sneezing. The worst that could happen to you in terms of being infected is getting a blast of sneeze from a contagious person. This would deposit virus-laden aerosols & droplets on your face and some could be ingested through your nose, eyes and possibly mouth. The physics of a typical sneeze varies from person to person (age, body mass, health, etc.) and with the ambient airflow (ventilation) regime in a given space.

Three important points to note when a person sneezes are: (1) a typical sneeze travels at velocity of around 45 m/s (100 mph) or more; (2) between 100,000 to 1,000,000 droplets are expelled (3) the travel distance of a sneeze could be up to 8 metres (m) away but the typical distance would be around 2m to 3m. The virus-laden aerosols and droplets from an infectious sneeze person would fall and contaminate nearby surfaces (laptops, keyboards, desks, mobile phones, handrails, pens, books, ATM or POS keypads, etc.) as well as the floor. Therefore, it is not only our hands that need regular sanitising: if you share any of the above objects, think again!

Even after a sneeze, some droplets would remain in aerosolised form (i.e. suspended in the air) for up to 10 minutes and possibly much longer. Sometimes they remain in the air for hours, depending on the ambient ventilation system. The airflow in a space dictates how long the ejected aerosols remain in the air and whether or not they are transported to other rooms, e.g. via centralised air-conditioning systems.

Second, we should examine coughing. A cough is similar to a sneeze, but ejects between 3,000 and 10,000 droplets (depending on the person) which travel at velocity of up to 20 m/s (40 mph) or more. The travel distance of such droplets could be as far as 6m away, but a distance of 1m or 2m would be typical.

The third area I’d like to cover is talking and breathing. Exhaling of air or talking by from a person also emits aerosols and droplets.

This is where it gets a bit more interesting (or dangerous, if you like) because: (a) talking for 5 minutes can emit as much aerosols as one cough; (b) aerosolised pathogens would spread faster in a noisy cafeteria than in a quiet study; (c) singing generates six times as much bio-aerosols as talking; (d) coughing 100 times generates around 120 litres of exhaled air and by comparison, breathing for 2 hours could generate up to 1,600 litres of exhaled air, while talking for 2 hours could generate 1,400 litres of exhaled air.

In summary, your main problem might not be the person coughing across the room but the quiet one sitting next to you for that 1-hour meeting or train/bus ride! Those who wonder why social distancing (staying at least 2m apart) is “imposed” would surely see the sense in it now.

Social distancing is vital and pending the emergence of a vaccine, remains our cheapest, safest and most effective tool in the fight against Covid-19! Be wary of standing/sitting too close to people whom you have absolutely no reason to be close to in this critical period.

In conclusion and from a transmission point of view, it would not matter if you wash or sanitise your hands 300 times in a day but do not maintain social distance. Okay, so your hands are now squeaky clean, well done, but infectious droplets (from other people sneezing, coughing, breathing or talking) have dropped on your face and clothes.

Last but not the least; I’d like to address the utility of facemasks.  The best way to minimise the impact of ejected infectious droplets is at the source (nose/mouth) because afterwards, it might be too late.

Therefore, since it takes around 5 to 14 days for Covid-19 symptoms to show, I would prefer someone who was infectious (possibly without them knowing it) to be wearing a facemask when breathing, talking (or heaven forbid: sneezing/coughing) next to me. Also, it would be helpful for those at risk (e.g. nearby persons) to also have facemasks so that at least their nose and mouths are protected from taking in droplets emitted at the speed of car travelling at 100 mph.

Please, this is not an advisory for you to rush down to your pharmacy to buy 20 cartons of facemasks! We are in bigger trouble if our doctors, nurses, police officers and food distributors do not have enough facemasks on daily basis. These people need to be out there, working hard to keep us alive, healthy, safe and well-fed.

The information I have provided above is based on established scientific knowledge on infectious bio-aerosols and the dynamics of their transfer from research done on SARS, Bird Flu, Swine Flu and MERS.

Zulfikar Adamu wrote from the UK. The full version of the article (and recommended further reading) can be found at: https://www.linkedin.com/pulse/covid-19-air-sneeze-cough-five-minutes-talk-zulfikar-adamu

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