Results of serological survey indicate extensive spread of viral infection in city
The results to the first COVID-19 sero (serological) surveillance study conducted for Pune city have shown that 51.5% of the population surveyed in five ‘high-incidence’ wards within Pune civic body limits had developed antibodies.
The study indicates that there has been an extensive spread of infection in the five highly-infected wards sampled in Pune city, with seroprevalence ranging from 36.1% to 65.4%, across all types of dwellings.
The sero-surveillance samples were collected between 20 July and August 5, with random blood samples of 1,664 persons taken by teams from five ‘high-incidence’ wards in Pune city: Yerwada, Lohiyanagar-Kasewadi, Rastapeth-Ravivarpeth, Kasbapeth-Somwarpeth, Navipeth-Parvati.
The study was carried out by scientists and epidemiologists from the Indian Institute of Science Education and Research (IISER), Pune, under the guidance of Prof. L. S. Shashidhara; the Savitribai Phule Pune University (SPPU); the Christian Medical College (CMC) at Vellore in Tamil Nadu; and the Translational Health Science and Technology Institute (THSTI) at Faridabad.
The THSTI developed the enzyme-linked immunosorbent assay (ELISA)-based test which helped to detect the IgG (Immunoglobulin G) antibodies against the virus. The study was funded by a ₹75 lakh-grant from the Persistent Foundation.
The presence of antibodies indicate that the individual was infected in the past and mounted an immune response to the infection. “While our tests estimate the presence of IgG antibodies against SARS-CoV-2 in a substantive portion of the population [in the selected wards] and suggest past infection, it does not necessarily indicate that the individual is resistant to subsequent infection. Neither is the high seroprevalence necessarily an indicator of population-level immunity,” said Dr. Aurnab Ghose of IISER, who was one of the principal investigators of this survey.
Given that Pune city, with nearly 15,000 active positive cases and over 1,800 deaths was a virus hotbed, Dr. Ghosh said one of the chief objectives of the survey was to help understand whether or not a second wave of infection would hit the city.
Remarking that the results, coming on the heels of similar surveys in Delhi, Ahmedabad and Mumbai were not particularly surprising, Prof. Shashidhara said the rationale behind serological testing for antibodies in a representative sample population was to estimate the cumulative incidence of infection in the population.
“Seroprevalence identifies infections that were asymptomatic or symptomatic but undetected. Such data provides insights into the trajectory of the disease and has implications for clinical management and public health control strategies,” he said.
Results showed that seropositivity (the state of having or not having detectable antibodies against a specific antigen) of 43.9% was observed among people residing in bungalows, while it was 56-62% among those in tenement or hutment dwellings. Participants from dwellings with shared toilets have higher seroprevalence, although a large proportion of people living in residences with independent toilets were also seropositive.
“People who lived in apartments had a somewhat lower prevalence (33%.) The prevalence was lower (45.3%) among people with access to independent toilets as compared to those who shared toilets (62.2%),” said Dr. Ghose.
The study revealed that there was no difference in seropositivity between men (52.8%) and women (50.1%). While people above 66 years of age had a lower prevalence (39.8%), the prevalence was similar across age groups below 66.
“A caveat here is that The results of the survey do not mean that these antibodies stop the virus from entering. There are reports from Wuhan in China and the U.K. that these antibodies wane after some time. Till we understand that, we cannot say anything definitively,” Dr. Ghose said.
On the sampling strategy, Dr. Ghose said an independent team of geospatial experts randomly selected 63 of 235 polygons with roughly equal area covering the five selected wards.
“The survey team started at the centre of the grid and collected samples from every fifth house. Every fifth home was sequentially selected in multi-occupancy tenement buildings. The study included all types of dwellings — hutments, tenements, apartments and bungalows — falling within the selected grid. One adult individual was selected from each household using a matrix to ensure appropriate age or gender balance,” he said.
Adults of 18 years and above from residential areas who self-reported no known acute illness at the time of collection were included in the study. No sampling was done in active containment zones.
Pune Divisional Commissioner Saurabh Rao said this was part of a series of surveys which will be conducted in Pune district. “Sassoon Hospital will soon begin its own survey that will focus on the Pune Municipal Corporation area. Dr. D.Y. Patil Medical College and Yashwantrao Chavan Memorial Hospital will conduct surveys that will focus mainly on the Pimpri-Chinchwad Municipal Corporation area,” Mr. Rao said.