Explained: How far can someone without symptoms transmit Covid-19 infection?

Testing at a facility run by municipal authorities in Mumbai. (Express photo of Ganesh Shirsekar)

Two recent figures released on separate days by the Indian Council for Medical Research (ICMR) about people with no symptoms testing positive for the new coronavirus disease (COVID-19) have raised fears that unsuspecting people suddenly get sick and sick. infecting others. A look at the evidence and guidance on asymptomatic cases of COVID-19:

What has the ICMR said about this?

On April 20, Dr. R R Gangakhedkar, chief of epidemiology and infectious diseases at ICMR, said: “I have explained that 80% of people will have infection without symptoms. They will be asymptomatic, but if you test them, there is a possibility that they are positive … We have to understand that the RT-PCR test is positive only after a person is symptomatic. People take time to be symptomatic. This means that if I examine him when he is asymptomatic, the chances that he will be positive are small ”. This, he said, is a limitation of the test: the closer you are to the point of infection (when the disease contracts and does not manifest), the less likely you are to test positive. That’s also why, he said, India’s testing strategy, which depends largely on whether a person is symptomatic (unless one is at an access point with a known history of contact with a case. confirmed), does not need any immediate review.

The next day, after this sparked fears, Dr. Gangakhedkar clarified that in India, 69% of people who tested positive are asymptomatic. “What I said yesterday about 80% of people is based on a single study,” he said.

What is the evidence for this?

It is now widely understood that worldwide, most people who become infected will show no symptoms, and will probably not even know they have contracted the virus unless they undergo serological testing at some point and are found to have developed Antibodies Last week, a study from China concluded that 44% of cases who had contracted the disease had contracted it from an asymptomatic person. They estimated that viral shedding, which is when one person infects another, begins to occur two or three days before the onset of symptoms.

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“We observed the highest viral load on throat swabs at the onset of symptoms, and inferred that infectivity peaked on or before the onset of symptoms. We estimate that 44% (95% confidence interval, 25-69%) of secondary cases were infected during the presymptomatic stage of the index cases, in settings with substantial family group, active case search and quarantine outside the home ” The researchers, including from Guangzhou Medical University and the Collaborating Center of the World Health Organization (WHO) for Epidemiology and Infectious Disease Control, at the University of Hong Kong, reported the study was published in Nature Medicine.

But what is the “presymptomatic stage”?

The WHO recognizes three stages of transmission of COVID-19: asymptomatic, presymptomatic, and symptomatic. “Symptomatic transmission refers to the transmission of a person while experiencing symptoms. Data from published epidemiological and virological studies provide evidence that COVID -19 is transmitted primarily from symptomatic persons to others in close contact through respiratory droplets, by direct contact with infected persons, or by contact with contaminated objects and surfaces. ” says the WHO. The incubation period for the virus ranges from 5-14 days. Presymptomatic transmission is when a person spreads the disease before symptoms appear and eventually develops symptoms on their own.

On asymptomatic transmission, the WHO says “it refers to transmission of the virus from a person who does not develop symptoms. There are few reports of laboratory confirmed cases that are truly asymptomatic, and to date, no asymptomatic transmission has been documented. This does not exclude the possibility that it may occur. Asymptomatic cases have been reported as part of contact search efforts in some countries. “

The US Centers for Disease Control and Prevention (CDC). USA They are clear that presymptomatic and asymptomatic transmission of the virus is possible. “The onset and duration of viral clearance and infectivity period for COVID-19 are not yet known. SARS-CoV-2 RNA may be detectable in the upper or lower respiratory tract for weeks after disease onset, similar to MERS-CoV and SARS-CoV infections. However, detection of viral RNA does not necessarily mean that an infectious virus is present. There are reports of asymptomatic infections (virus detection without symptom development) and pre-symptomatic infections (virus detection before symptom development) with SARS-CoV-2, but their role in transmission is not yet known. According to the existing literature, the incubation period (the time from exposure to the development of symptoms) of SARS-CoV-2 and other coronaviruses (for example, MERS-CoV, SARS-CoV) varies from 2 to 14 days ” , the CDC says.

People queue to eat at North 24 Pargana, Barasat, during the national closure (Express Photo: Shashi Ghosh)

How do you protect yourself from asymptomatic transmission?

There is no alternative to basic safety practices like washing hands, wearing a mask and social distancing, said Dr. Randeep Guleria, Director of AIIMS and a specialist in respiratory medicine. That is, until the moment a vaccine is found. “This is why universal precautions, such as social distancing, handwashing, are so important. Keeping your distance is very important, but stigma only ends up increasing mortality and morbidity. You have to understand that many people, especially considering how young our country is, would suffer a bit of fever and body pain and wouldn’t even know what COVID is. ”

The question of transmission from a person who does not show symptoms is also important: although the evidence on asymptomatic people who spread the disease may be divided, it is more or less accepted that people can transmit the disease before they have symptoms.

How long can a person transmit the disease after being infected with the virus?

It is often assumed that the answer to this question is 14 days. However, since it is a new disease, your knowledge is evolving. Recently, in Kerala, a 54-year-old woman tested positive for the virus nearly a month after her arrival from abroad, and has since been quarantined at her home. Health officials told The Indian Express that so far there have been at least a dozen cases of people testing positive after being quarantined for 28 days. On Thursday, Telangana decided to increase the period of home quarantine to 28 days, from 14 days. The Union Ministry of Health has advocated from the beginning for the monitoring of patients, at least through community surveillance, for 28 days and not 14 days.

This is also in line with some of the global experiences. In a study conducted last month in The Lancet Infectious Diseases, researchers at Imperial College London estimated that in China “the average duration from symptom onset to death is 17 to 8 days and to hospital discharge 24 to 7 days”. They also noted that all cases were hospitalized there, not so much because they needed hospital care, but to “prevent further transmission.”

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