NEW DELHI: The first national sero-survey by the ICMR, whose details were released on Thursday, shows that nearly equal proportions of people in urban and rural India had antibodies against coronavirus by early May.
According to the research paper published in the Indian Journal of Medical Research, 0.52% of those sampled in rural areas and 0.66% of those sampled in urban areas tested positive.
This could be an indication that in the country, the infectious disease had by then spread to the rural parts, despite government claims that the pandemic was still largely an urban phenomenon.
Overall, the seropositivity detected in 70 districts across 21 states stood at 0.73%.
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Samples for the survey had been collected between May 11 and June 4 from 28,000 people, whose blood samples were tested for IgG antibodies using Covid Kavach ELISA kit.
In the exercise, a total of 30,283 households were visited from 700 clusters in 70 districts.
The stratification of the districts as zero cases (15 districts), low (22), medium (16) and high (17) was done on the basis of the reported number of Covid-19 cases as on April 25. The seroprevalence across all four strata ranged from 0.62% to 1.03%.
Based on the seroprevalence rates, the researchers estimated a cumulative 6,468,388 adults by early May when the country had less than 60,000 confirmed Covid-19 cases.
The overall infection to case ratio was between 81.6 and 130.1; in other words for every confirmed case, 82-130 cases were being missed.
Also, seropositivity was found to be the highest among adults aged 18-45 years (43.3% among those who tested positive, 0.50% among individuals of this age-group in the survey), next among those aged 46-60 years (39.5% and 0.65%) and lowest among those older than 60 years (17.2% and 0.55%).
In the survey, nearly half of the participants were aged between 18 and 45 years and 51.5% were female. In all, 18.7% of the participants had an occupation with a high risk of exposure to potentially infected persons.
Also, 486 people reported a history of respiratory symptoms in the preceding one month, of whom, 44.7% sought medical care and 30.9% or 67 people, of those who sought care were hospitalised.