Sewage tests can help track the spread of Covid-19 infection: analysis
The fight against the coronavirus pandemic (Covid-19) is at a critical juncture. To measure the extent of infection, the Government of India now plans to expand randomized testing in areas with no reported cases. You will use a combination of the reverse transcription polymerase chain reaction, also known as RT-PCR, in pooled samples and antibody screening tests.
Another strategy that can help delineate areas with silent transmission is to analyze wastewater samples for the coronavirus (Sars-CoV2).
For now, we know that Covid-19 disease is caused by Sars-CoV2, and that in only 20% of cases, the severity of the infection requires hospitalization. In 30% of hospitalized patients, the virus was detected in samples from the respiratory tract and faeces. We also know that about 80% of infections are mild and do not require hospitalization. Among mild infections, the symptoms are mainly mild fever, mild cough, sore throat, runny nose, but also some gastrointestinal symptoms such as diarrhea, loss of appetite, nausea, and vomiting. These symptoms can occur alone or in combination with cough and sore throat. Patients with gastrointestinal symptoms have a longer duration of illness and pass the virus in their stool. In almost 25% of patients, nucleic acid particles are detected in the stool as early as three days after infection, even before it appears in the respiratory tract. (However, the virus is detected in the stool even in those who only have respiratory symptoms.) These findings suggest the importance of analyzing wastewater samples to detect Sars-CoV2.
In the past, sewage or wastewater monitoring has been used successfully to detect outbreaks of norovirus, antibiotic-resistant bacteria, measles, and poliovirus. Similarly, some countries have already started monitoring sewage / sewage for Covid-19. In Amsterdam, the virus was detected in sewage at Schiphol airport, just four days after the Netherlands confirmed its first case, long before the community reported the infection. Their samples have been found in untreated sewage in Tucson, Arizona. Sweden and Germany are also doing wastewater analysis.
Surveillance of wastewater can be an effective method of determining the presence of the virus in a community, even if people are asymptomatic for Covid-19. Furthermore, the density of the viral particles can give us an idea of the spread of the infection. This can also help us verify if interventions such as physical distancing reduce transmission. Periodic and periodic monitoring of wastewater can be an early warning tool to alert public health authorities of the likelihood of an increase in cases, giving them crucial advancement in preparedness.
Since it is not possible to assess everyone in a community, wastewater monitoring has the potential to uncover positive cases within it. Such monitoring can also provide a better estimate of the spread of infection, as it can account for those that have not been tested, either show only mild symptoms or are asymptomatic. Wastewater sampling could also serve as an early warning about the appearance of clusters. It can also act as a sensitive indicator for the reappearance of the virus. Wastewater monitoring for Covid-19 in India is possible and feasible.
India does, however, have household examples to emulate. It is one of the first countries to use wastewater monitoring (also known as environmental monitoring) to detect silent transmission of poliovirus through elimination in the community sewer system. India used to rely on acute flaccid paralysis (limp survey). But it is a well known fact that paralysis occurs only in severe cases; many infected children clear the virus without having the disease as well. In 2001, environmental monitoring was started, with wastewater sampling conducted weekly at three sites in Mumbai, and by 2017, there were 42 wastewater sampling sites distributed in Maharashtra, Gujarat, West Bengal, Uttar Pradesh, Bihar, Punjab, Telangana and Delhi. We have trained human resources to carry out wastewater monitoring for Covid-19. It can be an effective tool, especially in states with a large number of cases.
Given that the infection was reported in December in China last year, we know some of the critical information about the virus, but there are still a lot of unknowns. One of these unknowns is if virus particles are detected in the faeces, can they transmit through the faeces? Scientists have detected high concentrations of viral particles in feces, but so far they have not observed replication in the virus. However, current evidence does not support fecal transmission of Covid-19 through feces, monitoring of wastewater can act as a marker related to the infection of many things. It’s worth a try.
Dr. Lalit Kant is an infectious disease epidemiologist. He is the former head of the Division of Epidemiology and Communicable Diseases and senior advisor, Infectious Diseases, PHFI
The opinions expressed are personal.