NICD's top epidemiologist: How the Covid-19 pandemic is evolving and why we should be concerned

A top epidemiologist has warned the Covid-19 epidemic is evolving in the country.

This means it has moved from the importation of cases to low level local transmission whereby people, who have not yet been tested for the virus, are spreading it to their families and other contacts.

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This according to Professor Cheryl Cohen, the co-head of the National Institute for Communicable Diseases' Centre for Respiratory Diseases and Meningitis and an associate professor of epidemiology at the University of the Witwatersrand, who spoke to News24 on Thursday in a wide-ranging interview.

And as winter looms, millions of South Africans will contract the flu and, in the process, identifying cases of Covid-19 would become "very, very difficult", Cohen said.

There are almost certainly cases in our communities which have not yet been identified, a fact that President Cyril Ramaphosa alluded to in a televised address to the country on Thursday night in which he announced a two-week extension to restrictions. 

Ramaphosa said the current drop in new daily infections, down to 4% from 42% a day before the lockdown, was evidence it was working.

So far, 2 028 people have tested positive for the virus, and 25 have died.

Cohen said the slump in new cases was attributable to the travel ban, and the true effects of the lockdown would be measurable in two weeks from now.

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According to her, the lockdown had bought the country time to prepare and roll out mass testing campaigns intended to identify cases in communities, find hotspots of infections and take measures to prevent further spread in those areas.

Levels of testing are yet to reach ambitious levels of more than 30 000 per day as intended by the National Health Laboratory Service.

"We expect the [number of] cases may come up. It's also accepted the number of cases we see reported is not all the cases. Nobody is saying that's all the cases in SA," Cohen said.

"The epidemic is in a sense evolving. What we saw in the beginning, with the exponential increases in numbers, the vast majority of that was importation of cases and it was reflecting in fact, the exponential growth in other parts of the world that are ahead of us on the curve." 

Sting in the tail

The mildness of the symptoms that would arise in the majority of people who contract the virus, Cohen described as "the sting in the tail" of Covid-19.

Evidence and studies from other countries showed that roughly 80% of people who contracted Covid-19 would only have mild symptoms but would still pass on the virus to others.

Other coronaviruses, such as SARS or MERS, have a higher fatality rate but were easier to identify due to the seriousness of the symptoms making it much easier to contain. Those coronaviruses were also only contagious later on in the onset of symptoms.

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Covid-19 can be passed on early, sometimes days before any signs become clear.

"We're in that phase now. We know that there is likely local transmission at a low level and we know that even though we are scaling up testing a lot, it's very difficult to identify every single case, there really are tens of thousands of people every week in South Africa who have a fever or a cough," Cohen said.

Zweli Mkhize

Professor Cheryl Cohen (left) with Health Minister Zweli Mkhize during a press briefing on 5 March. Photo: Jan Gerber/News24

With winter fast approaching and the accompanying rise of flu infection rates, the detection of cases would be made even more difficult because Covid-19 symptoms are non-specific and closely mirror symptoms of other normal respiratory illnesses such as the flu.

Many people would not seek to test for Covid-19, or medical treatment.

"In that ocean of people with respiratory illness, it's not easy to find the Covid cases," said Cohen

In September 2019, a study she co-authored on the flu burden in South Africa found that on average, 10 million people in the country contracted the flu every year.

"The world was waiting and preparing for another influenza pandemic," Cohen said.

Instead, the coronavirus outbreak has brought with it a virus that would equally affect affluent and less affluent communities.

Equal opportunity killer

South Africa's first confirmed Covid-19 case on 5 March was a Hilton, KwaZulu-Natal, man who had returned from a skiing trip in Italy on 3 March. He was part of a group of 10 travellers who had returned to the country.

His wife became the second confirmed case and both have since recovered, but by the end of March, South Africa was seeing a rise in daily confirmed cases of anywhere between 100 and 200 cases per day.

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Since the lockdown, the number of daily confirmed cases has dropped to between 20 and 90 per day.

The majority of those early cases were as a result of travellers returning from the US, UK and Europe which at the time were already experiencing exponential infection rates that had gone undetected.

"There was some local transmissions which are expected from those cases to their contacts, but it wasn't really reflecting an exponential expansion in South Africa. It was reflecting a lot of importation," Cohen said.

Residents of Alexandra getting tested for Covid-19

Residents of Alexander informal settlement being tested for Covid-19 by a health worker. Photo: Nomvelo Chalumbira

She added a lot was done to identify those cases and to trace their contacts to contain and reduce the transmission of the virus, and these efforts likely had a substantial impact.

"But what we also know from what we have seen in other parts of the world and what we know about the disease, because this disease can present mildly symptomatically and because you can't pick up everyone at the border, so you do need to rely on people self-presenting and self-isolating afterwards, we know it is likely there were additional cases that we didn't pick up.

"Those additional cases may have spread the disease to their contacts which would lead to the local transmission which we know is going on."

A study by the University of Texas in Austin published this week, found for every one case identified there could be as many as 50 unidentified cases in some parts of the US. A faltering early response by the Trump administration has resulted in an explosion of cases in the US. New York has been particularly hard-hit.

Cohen mentioned similar studies which indicated a lower number of hidden cases - around 10 for every case identified.

Poor and rich alike at risk

If the country did see a significant increase in cases, affluent and less affluent alike would be equally affected, she said.

There was concern that the impact of the spread would be harder to contain in areas where people live in crowded conditions, such as informal settlements.

But this was clearly on the government's radar, and work started weeks ago to identify facilities where less affluent people could be taken to self-isolate if they were found to be infected with Covid-19.

"I think this is a respiratory disease and so there is a possibility that it will become more widespread within SA as it has done in Europe and America, and other countries. We know from other respiratory diseases … they effect equally the more affluent and less affluent sectors of the population. 

"What's very striking about the coronavirus disease, because of its mode of transmission, all communities are equally at risk of acquiring it."

Cohen warned against complacency and emphasised this virus would be with us for some time until a vaccine had been found which could take up to two years.

Social distancing in one form or another would likely continue, she said.

"Should the disease become more widespread, it is highly likely that it will affect all sectors of society. But obviously there is the concern is that the impact, the rate of spread, might be more in a crowded setting."

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