Traces of Sars-CoV-2, the virus that causes the coronavirus disease (Covid-19), have been found in sewage samples in Gujarat, prompting a central agency to consider strengthening surveillance and study whether contaminated sewage can cause infection.
“The next step obviously is to determine whether there is risk of infection through this channel or not. However it will still take some time before we start on that as currently there are several surveillance initiatives that need immediate attention,” said an official in the Union ministry of health, requesting not to be identified.
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Only Gujarat has so far reported the presence of the virus in sewage, “and we need to see if other states also report it,” the official added. “We will continue sewage sample testing for some time.”
Taking the help of its robust polio surveillance system that regularly tests sewage samples for presence of polio viruses, India’s National Centre for Disease Control (NCDC) started sewage sample testing to detect the presence of the Sars-Cov-2 virus in an attempt to strengthen Covid-19 surveillance.
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{{/usCountry}}Such surveillance has been a key component of India’s successful fight against he poliomyelitis virus that enters through the mouth and multiplies in the intestine. Although India has been polio-free since 2011, surveillance is still underway because the disease is still endemic in three countries--Pakistan, Afghanistan and Nigeria.
“We have World Health Organisation (WHO) reference lab for polio surveillance which conducts tests on regular basis on sewage samples to check for the presence of polio viruses. The same lab and its surveillance system, including manpower, is being used to monitor the presence of Sars-Cov-2 in sewage samples,” said the official quoted above.
NCDC, which spearheads all disease surveillance projects in the country, along with its partners, began sewage sample testing around April. The focus states were Gujarat, Maharashtra and Delhi that had a high Covid-19 disease burden.
“Though there is enough evidence to prove that the disease does not follow the faecal–oral route of transmission, there is no harm in expanding the scope of disease surveillance to be able to know the spread of the disease better, especially since we have a monitoring system and an advanced lab already in place for the purpose,” said an official in NCDC, who did not wish to be identified.
Faecal shedding is a common phenomenon in any viral diseases, and there is enough evidence to show that those individuals who are Covid-positive shed the virus through stool.
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“Studies show that the virus does travel to the gut in a Covid person with a high viral load. It is not unexpected to find the presence of this virus in sewage. What the surveillance system will be monitoring, however, is that if the contamination in the sewage system is happening to the extent that it will lead to transmission of the disease,” said the official.
At the local level, scientists from the Indian Institute of Technology in Gandhinagar, who collaborated with the Gujarat Biotechnology Research Centre and the Gujarat Pollution Control Board to study samples of wastewater collected on May 8 and May 27 from one of waste water treatment plants in Ahmedabad, also found traces of Sars-CoV-2.
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In an early release study published online in Emerging Infectious Disease Journal, researchers had isolated Sars-CoV-2 from faeces of a patient in China with Covid-19 who died. “Confirmation of infectious virus in faeces affirms the potential for faecal–oral or faecal–respiratory transmission and warrants further study,” the paper said.
“The virus is believed to be spread by direct contact, fomites (particles deposited on surfaces), respiratory droplets, and possibly aerosols. Viral RNA has been detected in faeces and urine of some patients. Infectious virus was also isolated from urine of a patient with severe COVID-19. However, it is unclear whether the virus in faeces is infectious and might be an additional source for transmission,” the paper added.
Sewage sample testing can be a good surveillance tool along with sero (blood) surveys, say experts.
“SARS may have spread through sewage in Hong Kong and now new data on infectious SARS CoV-2 in stool. Was this an unusual patient or will this route of transmission be a major player? At the very least, we should think about more sewage sampling,” tweeted Gagandeep Kang, physician-scientist and faculty, Translational Health Science and Technology Institute.