The world is changing fast and to keep up you need local knowledge with global context.
Protection for medics must be a priority in the Covid-19 pandemic, says Professor Robin Wood, a global expert on the aerobiology of infectious disease transmission, during a MedicalBrief webinar this week. Health workers as well as the public should wear masks, and doctors should consult remotely when efficiently possible, as “they are on the frontline of our ability to cope with this pandemic”.
Wood indicated that surgical masks and other medical masks should be prioritised for health care workers but well-made cloth masks could be worn by everyone.
In drawing parallels to his research into TB transmission, Wood also said his work indicated that under certain circumstances people who are not very TB infectious can transmit the disease. This appears to be the case, too, with Covid-19. In his TB research he notes that aerial transmission of TB can occur not only through coughing or sneezing, but also with very deep breathing. This could possibly also occur with Covid.
The apparent ease and rapidity of coronavirus transmission makes widespread wearing of masks advisable – a view that in recent weeks has been increasingly supported by research and now also by organisations including the US Centres for Disease Control and Prevention, which previously advised that masks were not a useful coronavirus precaution outside of medical settings.
Wood, of the University of Cape Town‘s Institute of Infectious Disease and Molecular Medicine and director of the Desmond Tutu HIV Centre, spoke at a well-attended MedicalBrief webinar held on Tuesday 7 April and titled COVID-19 transmission: Aerobiology research implications for hospitals, medical practices and everyday life.
“It is incumbent on the medical profession to deliver their medical care. If they can do it efficiently remotely, then that would be preferable,” the professor says. “But I don’t think that’s ever going to be a total substitute for meeting patients and interfacing with them at close quarters.”
In COVID-19 circumstances, giving medical professionals appropriate and proper personal protection is key. N95 masks should be used to protect medical staff.
“They should not be using inadequate masks multiple times that are meant to be used once. They should be in well ventilated areas.” This is no easy task. Even America, the world’s richest country, has hit a crisis of protective equipment. “They’ve run out and they’re using masks multiple times instead of once,” Wood points out.
Wood said he has been surprised by the number of medical people in China who contracted COVID-19. “The first person who recognised the disease, died of the disease. So there is transmission taking place between patients and staff who actually know about this.
“There is an urgency, to my mind, to get testing and protection equipment for medical staff.”
Wood was asked, among other things, about implications for medical practitioners of his research into the aerial transmission of viruses.
“I set off a few years ago to try and understand TB transmission, because we have more TB today than we had 100 years ago. It seems to be a fundamental of any disease control that you want to stop people catching it. We never really put a focus on that for TB, although we have a tremendous focus on that for Covid-19.
“I think the reason is that the response time from getting infected to disease is very short; it is in days with Covid whereas with TB it is longer, and that always confuses humans.”
For the past 140 years, people have generally felt that TB transmission was via the most symptomatic people. One reason for this belief could be because it is true; another could be that the test for TB is not very good. “A sputum test is about 50% sensitive, and at the time we didn’t have any way of measuring aerosols,” Wood says.
“So I thought, let’s see if we can apply a bit of technology to this, and firstly try and capture very efficiently what’s coming out of people. That sounds simple but it isn’t because a cough – everybody’s infatuated with coughing – comes out at about 40 metres per second.” To capture that is very difficult, but Wood overcame the challenge. “We capture coughs coming out at that sort of speed and we can capture every other respiratory manoeuvre that is less than that.
Combined with this was a need to find a way of detecting the organism that is much better than all previous ways. “So we then developed, with colleagues in America, a probe which could identify a single live organism. So we could see that it was live and was picking up these probes and we could look at it under a microscope.”
The combination of capturing coughs and detecting organisms changed views about TB. “Instead of thinking that with TB only the most infectious people – the sero-positives – are transmitting, we can now identify organisms in a short period of time from everybody who has got TB.
Obviously it varies from high numbers to low numbers, but that changes the whole story, says Wood. It gives credence to the possibility that under certain circumstances, people who are not that TB infectious can transmit the disease.
“Then we come to the question of how much air are people swapping.” People probably swap about 25 litres of air with other people per day – but if you are in Pollsmoor prison, you would be swapping 2,000 litres with other people.
There are three components to aerial infection: the number of people in a space, the ventilation in the space, and the time spent in the space. So a short time in a minibus taxi, which opens a large part of its side at regular intervals, is far less infection-risky than a minibus taxi driving between provinces.
“So what we are now saying is that under poor social circumstances, people who are not as infectious and couldn’t infect if you’re only exchanging a little bit of air, could be infectious. And we think that this is probably what’s been driving the TB epidemic in South Africa, amongst our poor populations.” This bodes ill for the fight against Covid-19.
Parallels with Covid
Covid modelling papers are saying that around 80% of cases are probably related to asymptomatic carriage – transmission from an infected person who displays no signs or symptoms.
“I believe the same thing for TB – we can only identify 30% of TB in our country where we can link it to someone who infected them,” says Wood. Both TB and Covid-19 are airborne diseases, he continues: “They are not identical, but we can learn some messages from both.”
One important message from Wood’s research is that in the periphery of the lung – the peripheral air spaces where pneumonia takes place – particles being produced and organisms being exhaled are totally independent of coughing or sneezing.
A lot of work and ways of trying to interfere with Covid-19 transmission are extrapolated from flu. “Well, flu is an upper airway disease and there is no doubt that if you exhale at very fast rates of 40 metres per second with a cough, you will vibrate all your upper airways from your voice box to your nose and your pharynx. So you will get a sample of upper airway particles.
But the Wood data shows that just taking deep breaths can produce as many organisms from the periphery of the lungs, “which is what we’re doing with TB”. Chinese research found that a throat swab as 20% to 30% sensitive to Covid, while taking a sample of peripheral lung fluid – which is what the Wood research does – is 93% to 97% sensitive.
“So it seems, if you apply a bit of intuitive common sense, that if you want to diagnose a periphery lung disease then a sample from there is appropriate; if you want to diagnose an upper respiratory tract infection, then swabs of the upper respiratory are appropriate.”
The problem is that Covid-19 does both. It presents in some people with shortness of breath straight away, which would indicate lower lung disease, while other people may have an upper respiratory tract infection. “Which are the samples you should be looking at? My quick answer to that is that you should be looking at both upper and lower, and we’ve developed the technology to do that.”
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