The seroprevalence of 7.75% in Indore indicates more than 2 lakh individuals have had SARS-CoV-2 infection in the recent past — at least 15 days prior to sample collection, said the city’s first such survey.
The community-based cross-sectional study, conducted from August 11 to 23 on 7,103 individuals residing since March 1 in Indore, the largest city of Madhya Pradesh also the worst hit by COVID-19, noted 2,03,160 individuals had the infection. The seroprevalence is much lower than that of Delhi, Ahmedabad, Kolkata and Mumbai.
Prevalence in hotspot areas is almost five times that in low risk areas. Further, the prevalence is the highest in 45-60 years age group followed by the above 60 years age group, said the survey coordinated by the Mahatma Gandhi Memorial Medical College, Indore and the National Centre for Disease Control, New Delhi. The study aimed at estimating the presence of anti-SARS-CoV-2 antibodies assayed from blood samples of the residents.
Not a marker of total or partial immunity
The Bambai Bazaar ward recorded the highest seroprevalence at more than 30 followed by another four wards where a prevalence of 20-25% was recorded. “Prevalence in hotspot areas is more and matches with surveillance data,” the study said, while noting the presence of antibodies are not a marker of total or partial immunity.
Both males and females recorded a near identical seroprevalence. Samples were picked using the stratified random sampling method where 33% males aged 18 and above, 33% females aged 18 and above and children between a year-old and 18 were picked. Only one sample from one household or family was collected.
The study noted public health control measures — strict containment, control and social distancing — “have been successful” to limit the spread. However, approximately 90% of the population is still susceptible to COVID-19. Non-pharmaceutical intervention with focus on high risk groups needs to be continued to prevent further spread of the infection.
“The results show the containment strategy has worked dramatically,” believes Salil Sakalle, Professor, Community Medicine Department at the college. “The results are a reflection of the transmission in April, May and parts of June. In hotspots, the antibody prevalence is higher which indicates the administration has succeeded in limiting the disease to hospots and prevented the possibility of community spread at that time,” he said.
Further, as regards the rising case count from July, Dr. Sakalle said it could be captured perhaps in a survey three-four months from now.
