Hyderabad: A sewage sample-based epidemiological study by researchers from Centre for Cellular and Molecular Biology (CCMB) and Indian Institute of Chemical Technology (IICT) here has revealed that the overall number of potential Covid-19 infected people in the capital could be close to 6.6 lakh.
The collaborative study harvested sewage samples to estimate the number of potential infected individuals in the city. Sewage samples from 80 per cent of the STPs in Hyderabad were processed to detect the presence of SARS-CoV-2.
“Our study revealed that there are around two lakh people who are shedding viral materials in Hyderabad. Since only 40 per cent of the Hyderabad sewage reaches STPs, this data can be used to extrapolate the overall number of potentially infected people, which has turned out to be approximately 6.6 lakh, that is around 6.6 per cent of the city’s population,” the study said.
The 6.6 lakh potentially infected persons include symptomatic, asymptomatic, and also recently recovered individuals in a time window of about 35 days. “A conservative estimate of the number of active cases who are shedding the virus may be around 2.6 lakh. The findings are posted on preprint server, MedRxiv, which is yet to be peer reviewed,” the CCMB researchers said.
“Our finding clearly 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 a large infection rates at a given time. It explains why our healthcare system has been able handle reasonably well the situation during the pandemic. 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 the system in taking necessary measures”, CCMB director Dr. Rakesh Mishra said.
Sewage samples for studies
Individuals who are infected by SARS-CoV-2 shed virus not only through nasal and oral routes but also through faeces, which provides an opportunity to use sewage or wastewater samples to estimate the spread of the infection in a given locality or area. The SARS-CoV-2 in sewage samples is non-infectious, thus making sewage samples suitable for epidemiological studies. Estimating the spread is very important in identifying affected areas, and controlling the pandemic, the researchers said.
Since an infected person sheds viral material in faecal samples for up to 35 days, these studies will provide an overall estimate of the situation in a window of one month. The scientists said that out of 1,800 million litres water used daily in Hyderabad, 40 per cent was processed at different STPs.
While viral RNA is detectable in the inlet samples, the outlet (after treatment) samples of STP were largely clean (free from viral RNA) in this regard, indicating efficient treatment practices at the STPs, the study said.
All the experiments were conducted at the CSIR-CCMB Covid-19 testing facility and the teams included Hemalatha Manupati, Kopperi Harishankar and S.Venkata Mohan from CSIR-IICT and Uday Kiran, CG Gokulan, Santosh Kumar Kuncha and Rakesh K Mishra from CSIR-CCMB.