In a collaborative effort, CSIR-Centre for Cellular and Molecular Biology (CSIR-CCMB) and CSIR-Indian Institute of Chemical Technology (CSIR-IICT) processed sewage samples from major sewage treatment plants (STPs) in Hyderabad to detect the presence of SARS-CoV-2 viral RNA. While viral RNA is detectable in the inlet samples, the outlet (after treatment) samples of STP were largely clean (free from viral RNA), indicating efficient treatment practices at the STPs.

The study covered about 80% of the STPs in Hyderabad and revealed that there are nearly 2 lakh people who are shedding viral material. Infected people shed the virus through oral and nasal passages and also through faeces.

Since only 40% of the Hyderabad sewage reaches STPs, this data can be used to extrapolate the overall number of potentially infected people, which could be approximately 6 lakhs, that is, around 6% of the city’s population, which includes symptomatic, asymptomatic, and also recently recovered individuals in a time window of about 35 days. The findings are posted on preprint server, MedRxiv, which is yet to be peer-reviewed.

The finding indicates that a large proportion of the affected individuals are asymptomatic and did not need hospitalization. This is also in agreement with the observation that hospitalization rush or mortality is way lower than otherwise expected with such large infection rates. 

Such studies if carried out in coordination with civic bodies to identify the hotspots in the city and monitor the dynamics of the infection rate can assist authorities in taking necessary measures.