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Superspreaders: Asymptomatic or not?

The concept of COVID-19 “superspreaders” has been a hotly debated topic since the beginning of the spread of the disease. Details regarding these superspreaders are still being established, with several studies offering conflicting information — particularly regarding whether asymptomatic individuals can be superspreaders.


COVID-19 Coronavirus superspreaders blood test 2019-nCoV,SARS-CoV, MERS-CoV chinese infection blood test in Laboratory. COVID-19 cases concept. Illustration of first coronavirus death in India. Representation of coronavirus testing. Image credit: photovs / 123rf
Image credit: photovs / 123rf

A study published on June 3rd in Annals of Internal Medicine has noted that evidence suggests the possibility of asymptomatic people becoming silent super-spreaders of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus which causes the disease COVID-19. Such a possibility offers grim portents for India, where thousands of day labourers and migrant workers have flocked in droves from cities back to their home villages following job losses due to the quarantine. 

Though the Centre continues to assure that community transmission of COVID-19 is not occurring in India, this increasingly looks like wishful thinking. According to a report drafted by epidemiologists, public health practitioners and experts in preventive and social medicine, “community transmission is already well-established across large sections or sub-populations in the country.”

Should the superspreaders study prove true, community transmission may not only be inevitable in India, but may be so widespread by this point that it may be all but impossible to contain. As crowds of thousands gathered in a mass exodus to leave India’s cities, few wore any kind of masks or took precautions to prevent the spread of the disease. Physical distancing was not a possibility amongst the crowds. Should just a handful of individuals have been infected, and, according to the study, not even show symptoms of COVID-19, there is no telling how many may have been infected. 

As individuals return home to their villages of origin, the potential for the virus to spread through superspreaders is amplified. Many are returning to difficult to access rural areas with either non-existent or ailing healthcare infrastructure that in many cases only has the capacity for the most basic of medical procedures. As such, mortality rates in India could soon skyrocket as rural regions find the infection burgeoning without the ventilators and intensive care services to accommodate the cases.

“The likelihood that approximately 40-45 percent of those infected with SARS-CoV-2 will remain asymptomatic suggests that the virus might have greater potential than previously estimated to spread silently and deeply through human populations,” the study states. The study drew from a wide range of different affected regions across the globe, as well as data gathered from isolated infections on a number of cruise ships.

“Despite concerns about distinguishing asymptomatic from pre-symptomatic persons, data from four of five of the cohorts suggest that a small fraction of asymptomatic persons may eventually develop symptoms. In the Italian and Japanese cohorts, zero percent of asymptomatic persons became symptomatic. In the Greek and New York cohorts, 10.3 percent of asymptomatic persons became symptomatic. In the New York cohort, the figure might be as low as 3.4 percent because of the presumed diagnosis of endometritis in two of the three women who developed fevers.” 

The study would suggest that heavy precautions should be undertaken in order to monitor the flow of people between regions — a notion that the quarantine in India took into account. However, other studies and organisations have suggested entirely contradictory conclusions.

The World Health Organization (WHO), for example, says it still believes the spread of the coronavirus from people without symptoms is “rare,” according to Outlook India. They report that Dr Maria Van Kerkhove, the WHO’s technical lead on the response to COVID-19, said at a press briefing on Monday that many countries are reporting cases of spread from people who are asymptomatic, or those with no clinical symptoms. However, when questioned in more detail about these cases, Dr Kerkhove said many of them turn out to have mild disease, or unusual symptoms. An estimate from the WHO states that the spread of the disease from individuals who are asymptomatic accounts for an apparent six percent of cases.

“We are constantly looking at this data and we’re trying to get more information from countries to truly answer this question,” said Dr Kerkhove. “It still appears to be rare that asymptomatic individuals actually transmit onward…we have a number of reports from countries who are doing very detailed contact tracing. They’re following asymptomatic cases. They’re following contacts. And they’re not finding secondary transmission onward.”

Kerkhove has clarified her comments on the notion of the asymptomatic spread of COVID-19, stating “there are some estimates that suggest that anywhere between six percent of the population and 41 percent of the population may be infected but not have symptoms within a point estimate of around sixteen percent.” She added that “to truly understand how many people don’t have symptoms, we don’t actually have that answer yet.”

The WHO has noted that the majority of transmission from asymptomatic cases occurs either within the household, or in care homes. However, this does not negate this kind of transmission method.

In an Indian context, given the circumstances of the mass transit of migrant workers back to their home villages — and presumably the homes of family members who are likely to be older — this could indeed amount to a high number of new cases. Asymptomatic individuals, who have spread out to hundreds, even thousands of villages and towns could now be spreading the virus to older relatives within their family homes. These individuals may not be asymptomatic, and may spread the virus to others, or become seriously ill themselves. 

Asymptomatic spread must be treated seriously, as it presents a major opportunity for resurgence, even in countries that have taken control of the situation. In India, where cases are now surging, asymptomatic spread could become a major cause for concern.

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