Sewage samples from Chandigarh found positive for Covid-19

Naina Mishra

Chandigarh, January 12

In a first, sewage samples in the city tested positive for Covid-19. The samples were tested by the Department of Virology, PGI, as a mandate of the WHO-ICMR Centre for “environment surveillance for Covid-19”.

The PGI had started testing samples from wastewater treatment plants from Chandigarh and Punjab’s Amritsar in the month of December. The samples were collected from Diggian sewage treatment plant and BRD plant in the city.

“Samples tested in the month of December were found to be negative for Covid-19. After a surge in the Covid cases at present, virus has also been detected in the sewage samples. The samples are tested once per week from each site to monitor the trend,” said Prof Mini P Singh, virologist at the PGI.

The processing of sewage samples is different from the processing of samples collected from humans and is an important component of surveillance. In the past, similar technique has been used for the surveillance of polio. Polio virus is also excreted in the human faeces. Similarly, Covid-19 surveillance in sewage samples can be used as an epidemiological tool as a marker of virus transmission and appropriate preventive measures can be initiated in a particular catchment area.

Training was imparted to the faculty and the staff by the NIV, Mumbai, and a WHO team as this involves a specialised procedure to concentrate the virus in sewage samples.

Generally, one litre of sewage sample is concentrated for two to three days to 2-3 ml so as to improve the detection of SARS-CoV-2 RNA. Concentration is more important for untreated wastewater samples than primary sludge samples. After this, nucleic acid is extracted and purified so as to isolate SARS-CoV-2 RNA from the sewage mixture.

The sample is then tested on the RT-PCR machine to detect the presence of the SARS-CoV-2 virus via fragments of genetic material (RNA) in wastewater. According to the WHO, finding this RNA in wastewater means that one or more person in the community had likely excreted virus through faeces.

Dr Singh said seven to eight sewage sites of Delhi will soon start sending samples to the PGI, Chandigarh, for the detection of Covid-19.

Samples collected from two places

The PGI had started testing samples from wastewater treatment plants from Chandigarh and Amritsar in December. The samples were collected from the Diggian sewage treatment plant and the BRD plant in the city.