Bengaluru, Nov 4 (IANS): A sero survey conducted in September revealed that 1.93 crore people across Karnataka were infected by coronavirus or had the infection in the past," Health Minister K Sudhakar said on Wednesday.

"Out of an estimated 7.07-crore population in Karnataka, the study estimates that 1.93 crore (27.3 per cent) are infected or had the infection in the past," Sudhakar told reporters here.

The Health Department conducted the survey from September 3-16 to estimate corona prevalence in those aged 18 and above in 30 districts across the southern state.

Three groups of people were surveyed -- pregnant women, persons attending outpatient department in hospitals in low-risk category; persons moving in the community like bus conductors, vendors at vegetable markets, healthcare workers, individuals in containment zones and congregation settings like markets, malls, retail stores, bus stops, railway stations, in middle-risk category; and elderly and comorbid persons in high-risk category.

"The study used Rapid Antigen Test (RAT) and Reverse Transcription Polymerase Chain Reaction (RT-PCR) test for the diagnosis of acute infection," said Sudhakar.

Serum testing for Immunoglobulin (IgG) antibodies was conducted to know the protection offered by the immune response.

The survey used standard Indian Council of Medical Research (ICMR) protocols and ICMR approved laboratory network in the state.

Of the 16,585 people tested in the three categories, analysis was done on the results of 15,624, whose RAT plus RT-PCR and Covid-Kavach enzyme-linked immunosorbent assay antibody test results were matched.

"The overall weighted adjusted sero prevalence of IgG was 16.4 per cent. It suggests that in the surveyed population, 16.4 per cent of the people were infected in the past and found to have IgG antibodies against the virus," said Sudhakar.

In contrast, the seroprevalence of IgG in New Delhi was 29.1 per cent, in Mumbai 16 per cent in non-slum settings and 57 per cent in slum settings, in Pune 36.1-65.4 per cent, in Indore 7.8 per cent, in Puducherry 22.7 per cent and in Chennai 32.3 per cent.

The national survey ICMR conducted in 70 districts across the country showed a sero prevalence of 0.7 per cent in the first round (May) and 7.1 per cent in the second round (August-September).

All the surveys captured only the evidence of infection in the past (IgG). They were limited to capture information in metropolitan area.

"In contrast, the survey in Karnataka has captured total prevalence, including information on current and past infections," asserted Sudhakar.

At the state level, there were 40 undetected infected individuals for every RT-PCR confirmed case. The cases-to-infections ratio ranged from 10 to 111 across units.

In the national seroprevalence survey, the cases-to-infections ratio was 81.6 to 130.1 in the first round (May), which improved by the second round to 26-32 infections per case.

The surge in cases is yet to occur in districts (Dharwad, Gadag, Chikkaballapur, Bagalkot, and Mahadevapura in Bengaluru east) with the lowest estimated prevalence of the virus.

The study recommended district-level facility-based sentinel sero-surveillance to monitor the trend of infection in the long term.

"A follow-up survey is planned to assess the extent and speed of transmission and evaluate the impact of containment strategies over time in the state," added Sudhakar.