The sero survey carried out in five zones in Pune has found 51.5% seroprevalence, with the spread ranging from 36.1% in the lower bound to 65.4% in higher bound. The spread of the virus was found across all types of dwellings. Those living in hutments (62%) and tenement (56.2%) had the highest seroprevalence, while those living in bungalows (43.9%) and apartment (33.2%) had the lowest seroprevalence.

Results of a serological study carried out in five administrative zones of the Pune Municipal Corporation reveal “extensive spread” of novel coronavirus in the community. The sero survey results estimate 51.5% seroprevalence in the five zones studied, with the spread ranging from 36.1% in the lower bound to 65.4% in higher bound. The spread of the virus was found across all types of dwellings. The survey was carried out between July 20 and August 5.

“With the peak yet to reach, 51% seroprevalence is intriguing,” Dr Giridhara Babu, epidemiologist from Public Health Foundation of India, Bengaluru says in a tweet.

The five administrative zones of the Corportaion where the sero survey was conducted are: Yerwada, Lohiyanagar-Kasewadi, Rastapeth-Ravivarpeth, Kasbapeth – Somwarpeth, Navipeth-Parvati.

According to a report posted on the website of Savitribai Phule Pune University, the virus has spread widely across the five zones and in all types of dwellings. While those living in tenement (536 adults, 56.2%) and hutment (600 adults, 62%) dwellings recorded the most virus spread, seropositivity was 43.9% (82 adults) among those living in bungalows and 33.2% (446 adults) in people living in apartments.

The role of shared toilets in increasing virus spread has once again become apparent in this study. While the seropositivity was 45.3% among people (1,045 adults) who have access to independent toilets, 619 adults who share toilets have a high 62.2% seroprevalence. “There is no difference between men (n=861, 52.8%) and  women (n=803, 50.1%), while 171 persons of older age (above 66 years) have a lower prevalence (39.8%),” the report posted on the University website says. Those in the age group 51-65 years had the highest seroprevalence of 54.8%. Those in the age group 18-30 years and 31-50 had seroprevalence of 52.5% and 52.1%, respectively.

The survey was carried out by scientists and epidemiologists from Savitribai Phule Pune University (SPPU), Indian Institute of Science Education and Research (IISER) Pune, Translational Health Science and Technology Institute (THSTI), Faridabad and Christian Medical College (CMC), Vellore, Tamil Nadu.

Assuming 5% seroprevalence, the study needed to recruit 1,520 individuals to obtain a 95% confidence interval. In the end, the researchers recruited 1,664 adults over the age of 18 years. Only one adult was selected from each household to ensure “appropriate age/gender balance”, and only those with no self-reported acute illness at the time of sample collection were included in the study. No sampling was done in active containment zones, the report says.

Blood samples were collected from 1,664 consenting individuals, chosen as per the study design during the period July 20 and August 5. The blood samples were processed to detect the presence of IgG antibodies against the receptor binding domain (RBD) of the viral spike protein. The THSTI-RBD-ELISA assay, which has 100% specificity and 84.7% sensitivity was used for testing the samples. This assay has been extensively characterised and compared with other commercially available tests for SARS-CoV-2 IgG. The results of the comparative evaluation have been posted on medRxiv preprint server.