NEW DELHI: For every RTPCR confirmed COVID-19 case in India by early May, there were 82-130 actual cases of infection, the findings of the first population level national serosurvey carried out by the Indian Council of Medical Research has shown.
The study, which after nearly three months of the survey, has now been published in the ICMR’s Indian Journal of Medical Research also suggests that when India had less than 60,000 confirmed COVID-19 cases in —the actual infection size was over 100 times bigger.
“A cumulative 6,468,388 adult infections were estimated in India by the early May,” says the survey based on testing 28,000 individuals across 70 districts for the presence of antibodies against SARS CoV2.
The blood samples for the survey had been collected between May 11 to June 4.
The districts had been chosen based on high, medium, low and zero prevalence of the confirmed COVID cases and overall, 0.73 % of the samples tested had antibodies against the virus.
“The findings of the first national population-based serosurvey indicated that 0.73 per cent of adults in India were exposed to SARS-CoV-2 infection, amounting to 6.4 million infections in total by the early May 2020,” noted the authors.
The seroprevalence ranged between 0.62 and 1.03 per cent across the four strata of districts but interestingly the survey showed that the highest seroprevalence was in districts categorised as “medium” prevalence.
Also in “zero” prevalence districts--where there were no official cases -- 0.62 % of the population had exposure to the Covid19 virus.
“The high infection to case ratio in India could be on account of the prioritization of testing among symptomatic or the variability in testing rates across the states,” notes the study.
It also says that the infection fatality rate per 10,000 infections as on June 1 ranged between 0.27 in zero stratum and 15.04 in the high stratum districts.
The results of the first part of the survey have been released even as a second serosurvey is underway in the same districts. The second part of the exercise--which was to assess the true prevalence of the infection in containment zones in hotspot districts, however, is yet to be released.