Each Covid patient infected 12 others, shows serosurvey in Karnataka

High infection rate in 10 districts of Karnataka, fatality rate worrisome in 8 districts 
Each Covid patient infected 12 others, shows serosurvey in Karnataka

BENGALURU: For every RT-PCR confirmed Covid-positive patient, there were 12 infected individuals with detectable IgG (antibody) levels in Karnataka.

This is called the Case to Infection Ratio (CIR) and was revealed in the second serosurvey results. 

The CIR is high in Belagavi (1:39), Kolar (1:35), Chamarajanagar (1:35), Mandya (1:30), Kodagu (1:25), Bagalkot 1:24, Vijayapura (1:23), Ramanagara (1:22), Mysuru (1:21) and Chitradurga (1:20). 

On the other hand, the Infection Fatality Rate (percentage of fatalities out of total positives) was estimated at 0.11%, and is high in Dharwad (0.50%), Bengaluru Urban (0.34%), Haveri (0.29%, BBMP RR Nagar (0.28%), Hassan (0.28%), BBMP West (0.22%), BBMP East (0.21%) and Bidar (0.20%).

The authors of the study told TNIE that in anticipation of the third wave, districts with high CIR and low IFR should consider re-evaluating their testing strategies and death reporting.

Vaccination coverage should be stepped up, as is being done.

A third serosurvey is being planned and will provide valuable information for vaccination prioritisation, and revision of testing strategy.

“Dharwad has the highest IFR. This is most likely due to travel from neighbouring units to avail of critical or tertiary healthcare facilities. Further research should explore this hypothesis,” they said.

“Factors for high CIR in some districts can be attributed to virus mutants, population density ratio, laxity in Covid appropriate behaviour among people in interior locations, and living in larger families,” said Dr Satyanarayana Mysore, HOD and Consultant, Pulmonology, Lung Transplant Physician, Manipal Hospitals, while advocating a uniform metric to measure infectivity.

As for high IFR in some districts, we need to know how many patients were diabetic, how many presented late, if they underwent cytokine storm before reaching hospital, etc, Dr Mysore said. 

The serosurvey found seroprevalence was more among males (15.4%) than females (12%), high among the elderly than those aged below 30, higher among  rural population (15.4%) than urban dwellers (14%). 


Study sampled three population groups: low, moderate and high-risk groups 

Low-risk group comprised pregnant women presenting for regular check-up at ante-natal care clinic, attenders of patients coming to outpatient department in healthcare facilities 

Moderate-risk group comprised people with high contact in the community -- bus conductors, vegetable vendors, healthcare workers, pourakarmikas, individuals in congregate settings (such as markets, malls, retail stores, bus stops, railway stations, hotel staff) 

High-risk group comprised the elderly, persons with comorbid conditions

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