Sampling and isolating asymptomatic drivers of coronavirus before it spreads will aid in protection, writes Dr Kim Sawyer.
THE PROBLEM with the COVID-19 virus is that it hides better than other viruses.
We do not know how many are infected because we have not tested everyone. The asymptomatic are driving the virus. We need to identify them before they transmit the virus to the vulnerable.
The solution to the problem is to find those who spread the virus before they spread, rather than identify their cluster after they have spread. Many of the spreaders are asymptomatic. Many are young and healthy. We need to find them and to isolate them. Our strategy must be to test and to isolate those who test positive. Without a vaccine that is our only protection.
Coronavirus is now affecting almost 200 countries with nearly half a million cases and more than 300,000 active cases. Given the nature of the virus, there are probably many millions infected. The problem is we don’t know because we are not sampling the right way. We find a cluster after we find an infection. We need to begin to sample more widely. We need to sample the young.
Sampling has become important because there are two schools of thought on the contagion. One study by Oxford University’s Evolutionary Ecology of Infectious Disease Laboratory suggests half of the population of the United Kingdom may already be infected with the virus, in which case less than .01 per cent of those infected would require hospital treatment.
The other school of thought is from Imperial College, which suggests the contagion is in its early stages, that every country is on the same curve and that in the UK alone a quarter of a million will die if there is no prolonged shutdown.
Which hypothesis is correct? We do not know. The reason we don’t know is that we are not taking random samples of the population.
Consider how we usually sample a population. If we want to know how the population of 25 million will vote at a general election, we take a random sample of say 2,000 of the population. The problem with coronavirus is that it is not randomised. The virus spreads through population clusters. One person, often asymptomatic, can infect between two and six others. Population clusters whether at restaurants, football matches, schools, apartment complexes, or in households, are driving the contagion. We are identifying the clusters too late. We can stop the virus by stopping the clusters. We can also stop the virus by sampling across those we think may generate a cluster. We need to identify clusters before they form rather than after.
Population clusters are the key. In Italy, Bergamo became an epicentre of the contagion after 40,000 football fans from Bergamo travelled to Milan to watch their team beat the Spanish team Valencia. Mayor of Bergamo Giorgio Gori believes that this act started the contagion. The cluster in the Kirkland nursing home in Washington was an example where there were early indicators of respiratory problems, but the indicators were ignored. The cluster in the Hasidic Jewish community in Brooklyn was due to weddings that occurred a few weeks before. We stop the virus by preventing congregations. Cancelling the Grand Prix and suspending the AFL will be seen in hindsight as wise.
However, the most important cluster is the household. The experience in Wuhan showed that those who could not be admitted to hospital were forced to remain at home where they infected other members of the household. The household is a cluster where a virus can spread from the asymptomatic to the vulnerable. The virus spreads within households just as well as between households.
We must emphasise staying at home does not necessarily impart immunity.
Testing is now so important. To stop the virus, we must consider how to move to mass testing. Vo, the town in Italy where the first death occurred, provides the template. All 3,000 residents of Vo were tested by the University of Padua. When 89 people tested positive, they were isolated. In the second round of testing, only six were positive. Those six remained in isolation. Vo has had no more deaths. Vo eliminated the virus by testing and isolating the infected.
Testing and isolating should be the objective of every government.
Our problem is that we have 25 million people and not 3,000. We do not have enough tests for everyone to be tested, let alone re-tested. However, the countries that have been most aggressive with their testing – South Korea and Germany – have been some of the most successful in flattening the curve of the contagion. A government that is promising a stimulus package of many billions of dollars can surely afford to spend a billion on testing. The virus is the greatest risk for the economy. The only way to hedge the risk is to test.
While we do not yet have the resources for mass testing, we do have the resources to test samples of the population and not just those who appear with symptoms. This is important because those without symptoms or with mild symptoms are driving the virus. Globally, 95 per cent of current active cases have mild symptoms or no symptoms at all. The virus has power because it cannot be seen. The virus depends on the spread from the asymptomatic to the vulnerable.
Sampling will tell us whether we have the Oxford model of contagion or the Imperial model. Sampling may find the virus before the clusters form rather than after they form. Sampling the young may identify spreaders before they spread the virus. We cannot test everyone, but we can sample those who we think may be spreading the virus.
Dr Kim Sawyer is a senior fellow in the School of Historical and Philosophical Studies at the University of Melbourne.
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Australia License
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