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COVID-19 Superspreader

 What Makes Someone a COVID Superspreader
    It is known that the coronavirus is primarily spread from person to person through respiratory droplets which can be released in sneezes and coughs. As a result, many people might suspect that coughing or sneezing by an infected person makes them a 'super spreader' or more likely to transmit the virus to others. However, new research published in The Lancet Infectious Diseases on February 2, 2021 finds that what makes someone a COVID-19 superspreader is not how often one coughs or sneezes but instead dependent upon another factor. This post covers the methods and results of the conducted study and summarizes the overall findings. 

About the Study

    The study, conducted in Catalonia, Spain, was a randomized trial conducted between March 17 and April 28, 2020. Researchers conducted this study with the goal of answering the question 'what makes someone with COVID-19 more contagious.' To answer this question, the researchers monitored a group of 282 un-hospitalized COVID-19 patients (aka index cases) aged 18 years and older as well as 753 of their close contacts who were exposed to an index case during infection. The average age of the COVID-19 infected participants was 42 years and most patients (72%) were women.

Results

    Of the 282 index patients, 32% transmitted COVID-19 to at least one close contact. Researchers wanted to know what factor was associated with an increased transmission of the coronavirus from index cases to their close contacts. Contrary to what one might expect, there was no association between risk of transmission and respiratory symptoms. Instead, the viral load (amount of virus in the body) of the index case was strongly correlated with risk of contagiousness. The percent of COVID-19 positive contacts jumped from 12% at an index case viral load of 1 x 106 copies/mL to 24% at an index case viral load of 1 x 1010 copies/mL. While infection risk was also found to increase with the age of the close contact, there was no association between infection risk and age of the index case. 

As viral load of index case increases, the proportion of infected contacts increases
    
    Researchers also discovered that close contacts with a higher viral load were more likely to develop symptomatic COVID-19. The probability of a contact developing symptomatic COVID-19 with a viral load of 1 x 107 copies/mL or lower was 38%. Risk of developing symptomatic COVID-19 jumped to 68% in contacts with a viral load of 1 x 11010 copies /mL. Risk of developing symptomatic coronavirus was not associated with sex, age, or underlying diseases including respiratory diseases.

The higher the viral load of an individual, the more likely they will develop symptomatic COVID-19

Summary

    Overall, this study found that the determining factor in what makes someone a superspreader is not how often they might cough or sneeze but the viral load of the individual. A high viral load was also associated with an increased chance of developing symptomatic COVID-19. The findings from this study further highlights the importance of contact tracing individuals with high viral loads. Additionally, the results suggest that you should always mask up and social distance around others as you do not know their viral load/contagiousness. 

Sources

1. Marks, Michael, et al. “Transmission of COVID-19 in 282 Clusters in Catalonia, Spain: a Cohort Study.” The Lancet Infectious Diseases, 2 Feb. 2021, doi:https://doi.org/10.1016/S1473-3099(20)30985-3. 

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