For every confirmed case of Covid-19 in May, there were 82-130 infections that went undetected and India potentially had 64 lakh people infected with the virus, as per the results of the first sero-survey conducted by scientists from the Indian Council of Medical Research (ICMR).
The number could be on the higher side given that as the survey noted there could be under-detection of Covid-19 cases in the zero stratum districts on account of low testing as well as poor access to testing laboratories.
“The low prevalence observed in most districts indicates that India is in the early phase of the epidemic and the majority of the Indian population is still susceptible to SARS-CoV-2 infection,” said the study conducted on 28,000 people from 700 clusters in 70 districts across the four strata from May 11 to June 4.
The study is published in the latest issue of Indian Journal of Medical Research (IJMR)
The study wherein blood samples were tested for IgG antibodies using Covid-19 Kavach ELISA kit, indicated that 0.73 per cent adults in India were exposed to SARS-CoV-2, amounting to a total of 6.4 million infections by early May.
Also, seropositivity was the highest in the age group of 18-45 years (43.3 per cent), followed by those between 46-60 years (39.5 per cent) and it was the lowest among those aged above 60 (17.2 per cent).
It highlighted the need to continue to implement the context-specific containment measures including the testing of all symptomatics, isolating positive cases and tracing high-risk contacts to slow transmission and to prevent the overburdening of the health system.
Males, living in urban slums and occupation with high risk of exposure to potentially infected persons were associated with seropositivity.
According to the survey report, seroprevalence ranged between 0.62 and 1.03 per cent across the four strata of districts.
The stratification of districts as zero cases (15 districts), low (22 districts), medium (16) and high (17) was done on the basis of the reported number of Covid-19 cases as on April 25.
About one-fourth (25.9 per cent) of the surveyed clusters were from urban areas. Nearly half (48.5 per cent) of the participants were aged between 18 and 45 and 51.5 per cent (14,390) were females. In all, 18.7 per cent of the participants had an occupation with a high risk of exposure to potentially infected persons.
In four of the 15 districts in this stratum, Covid-19 testing laboratories were not available in district headquarters and the samples were transported to the state headquarter hospitals for diagnosis.