New Nimhans study shows asymptomatic persons can transmit Covid-19 to others

A new study of Covid-19 cases in Karnataka has found that asymptomatic persons can not only spread the disease to other people but that people without symptoms can also succumb to disease, although the chances are lower.

The study, which was conducted by researchers from Nimhans, the Indian Institute of Public Health and government officers from the State Surveillance Unit, considered 3,404 Covid-19 cases from the start out of the outbreak in March to May 31.

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Out of these numbers, 3,096 were people without symptoms while 308 had symptoms. The researchers hoped to discover the transmission rate by asymptomatic persons as previous reports “suggest that nearly 4-32% of the infections are spread through asymptomatic persons,” the researchers wrote.

Much of the study’s conclusions fall in line with what is already known about how Covid-19 affects people: that the occurrence about comorbidities is ten-fold higher in symptomatic cases: 87 people out of the 308, as is the fatality rate with 47 people perishing (38 of whom had comorbidities).

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However, the study findings regarding asymptomatic people offer some surprising insights: that the mortality among people without any symptoms is as high as 13%. Seven people with the sample studied, who did not have any symptoms or even comorbidities, died.

When it came to disease transmission, 2,136 or most of the people up to May 31, who had contracted the disease had done so during domestic travel. Another 873 had been infected by an identifiable Covid-19 patient. However, for 267 cases, the precise reason for infection was not known at all.

Surprisingly, the study determined that the “proportion of secondary cases manifesting overt clinical illness” is higher when the index case is symptomatic. Among 545 secondary cases which were studied, 43 were symptomatic and 616 were asymptomatic.

The 43 people with symptoms infected 659 others. Meanwhile, the 616 people without symptoms, infected 504 people.

The researchers admitted to two limitations with the study: the difficulty of distinguishing asymptomatic from those who are pre-symptomatic. In addition, contact tracing was available for cluster network analysis only in 966 out of 3404 Covid-19 cases, until May 31.