A sero survey done to estimate the prevalence of COVID-19 in Karnataka has found that while 16.4% of the 15,624 samples studied have developed antibodies against COVID, 12.7% was found to have current (active) infection.
Health and Medical Education Minister K. Sudhakar, releasing the findings on Wednesday, said the overall adjusted prevalence of COVID-19 in the State was 27.3% (combined IgG and active infection).
The survey done from September 3 to September 16, included the proportion of people who had COVID-19 infection recently and those currently having active SARS-CoV-2 infection. The sampled population surveyed were all adults aged 18 years and above. All 30 districts of the state, including eight zones of BBMP, were included in the survey. The survey was conducted in 290 hospitals and selected population settings, said Mr. Sudhakar.
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The study used Rapid Antigen Test (RAT) and RT-PCR for the diagnosis of acute infection. Serum testing for IgG antibodies was also conducted to understand the protection offered by the immune response. Standard ICMR protocols and ICMR approved laboratory network in the State were utilised, he said.
“Although 16,585 persons were surveyed covering the three risk categories (low, moderate and high), the analysis was done on results for 15,624 individuals whose RAT plus RT-PCR and COVID Kavach ELISA antibody test results were matched in the line list,” the Minister explained.
Giridhar R. Babu, member of the State’s Technical Advisory Committee (TAC) said as many as 19 districts have a high case to infection ratio (i.e., more than 40). “There is a need to improve detection of cases through syndromic approach here, to improve testing and ensure that other public health actions (avoiding 3Cs and following 3Ws) are implemented efficiently,” he siad.
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The 19 districts covered in the survey are Vijayapura, Belagavi, Chitradurga, Tumakuru, Raichur, Ramanagar, Haveri, Chamarajanagar, Bidar, Davanagere, Yadgir, Kalaburagi, Kolar, Kodagu, Mandya, Chikmagalur, Ballari, Bengaluru Rural, Hassan, Dr. Babu said.
Districts with a low case to infection ratio (BBMP Bommanahalli, BBMP East, BBMP West, BBMP South, Mysuru) suggest that the strategy employed for testing is reasonable and can be replicated in other districts, he said.
Out of 7.07 crore estimated population in Karnataka, the study estimates that 1.93 crore (27.3%) of the people are either currently infected or already had the infection in the past, as of 16 September 2020, he said.
As per ICMR’s second round of sero survey, the weighted and adjusted prevalence among individuals aged ≥ ten years was 6.6%, with urban slums having 15.6% and non-slum urban areas having 8.2%.
At the State level, it was estimated that there were 40 undetected infected individuals for every RT-PCR confirmed case, i.e., case-to-undetected-infections ratio (CIR) of 1:40. The cases-to-infections ratio ranged from 10 to 111 across units. In the national sero prevalence survey conducted by ICMR, the CIR was 81.6 to 130.1 in the first round (May), which improved by the second round to 26–32 infections per case.