23.7% have developed antibodies against COVID-19 in Belagavi, serosurvey finds

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. The study was conducted during 03-16 September 2020.

A survey to estimate the prevalence of COVID-19 in Karnataka state was done from September 3-16, 2020. This 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 hospitals and selected population settings. Three groups of the population were covered that included — (i) low-risk group, i.e., pregnant women attending the antenatalclinic, persons attending the outpatient department in the hospitals/attendees of children or patients; (ii) moderate-risk group, i.e., persons movingin the community likebus conductors, vendors at the vegetable markets, health care workers, individuals in containment zones and congregate settingssuch as markets, malls, retail stores, Bus stops, railway stations, pourakarmikas/ waste collectors; and (iii)high-risk group .i.e. elderly and persons with comorbidconditions.

The study used Rapid Antigen Test (RAT) and RT-PCR for the diagnosis of acute infection. At the same time, serum testing for IgG antibodies was conducted to know the protection offered by the immune response. The standard ICMR protocols were used, and ICMR approved laboratory network in the state was utilized.

• Of the 16,585 persons surveyed covering the three risk categories, 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 overall weighted adjusted seroprevalence of IgG was 16.4%. It suggests that in the surveyed population, 16.4% of the people were infected in the past and found to have IgG antibodies against SARS CoV-2.The overall weighted adjusted seroprevalence of IgG in Delhi was29.1%, Mumbai was 16% non-slum settings, 57% in slum settings, 36.1-65.4% across five prabhags in Pune, 7.8% in Indore, 22.7% in Puducherry, and 32.3% in Chennai. The national seroprevalence survey conducted by the Indian Council of Medical research found a seroprevalence of 0.7% in the first round (May) and 7.1% in the second round (August-September). Both rounds were conducted in 70 districts of the country. All these surveys capture only the evidence of infection in the past (IgG). The surveys done in other states were limited to capture information only within the confined limits of the metropolitan area.
• Compared to other studies in India,the survey undertaken in Karnataka has captured total prevalence, which includes information on both current and past infections. The participants were included from locations centred around 290 hospitals spread throughout the state of Karnataka at the district, taluk and rural areas. The survey employed all three tests: Rapid Antigen Tests,RTPCR, and antibody (IgG).
• 12.7% of the apparently healthy population in the surveyed area was found to have a current(active) infection.
• The overall adjusted prevalence of COVID-19 was 27.3% (combined IgG and activeinfection). As per the ICMR 2^nd round of serosurvey, 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 seroprevalence 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.
  • Districts with high cases infections ratio (i.e., more than 40) need to improve detection of cases actively through syndromic approach, improve testing, and ensure other public health actions (avoiding 3Cs and following 3Ws) are implemented efficiently. These districts were Vijayapura, Belagavi, Chitradurga, Tumakuru, Raichur, Ramanagar, Haveri, Chamarajanagar, Bidar, Davanagere, Yadgir, Kalaburagi, Kolar, Kodagu, Mandya, Chikmagalur, Ballari, Bengaluru Rural, Hassan.
  • 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.
• Out of 7.07 crore estimated populationin 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. The infection fatality rate due to COVID-19 was 0.05%.The infection fatality rate due to COVID-19 in the state of Karnataka is 0.05%. The districts with a high infection fatality rate suggest that clinical care needs to be improved in these places. The present IFR is likely an underestimate. The overall IFR based on the first round of sentinel serosurvey findings is 0.07%. The IFR reported across other cities are Mumbai (0.05-0.10%), Pune at 0.08%, Delhi is at 0.09, and Chennai is at 0.13%.

In summary, the state is passing through different stages of the COVID-19 pandemic in the different districts. The surge in cases is yet to occur in the districts with the lowest estimated prevalence of COVID-19 (Dharwad, Gadag, Chikkaballapur, Bagalkot, and BBMP Mahadevapura).The study recommends establishing the district-level facility-based sentinel sero-surveillance to monitor the trend of infection in the long term systematically. This can inform local decision-making at the district level to mount the necessary public health response towards the COVID-19 epidemic in Karnataka state.