It is a finding that raises many questions and could substantially modify what is known so far about the virus that causes covid-19.

Researchers from at least five countries, including Brazil, detected the presence of the new coronavirus in collected wastewater samples weeks or months before of the first officially registered case in the Chinese city of Wuhan, considered as the origin of the current pandemic.

But how do these stool virus findings affect what we know about the SARS-CoV-2 virus?

Scientists point out three main axes:

Monitoring: Sewage detection can serve as a comprehensive and inexpensive tool to monitor the progress of covid-19. There are at least 15 countries where this strategy has been adopted or is being studied. Possible health risk: the presence of the genetic material of the virus in the faeces indicates that wastewater may be a route of contagion. Origin of the pandemic: the virus may have circulated much earlier than indicated in the official timeline.

Regarding the third point, the study that caught the most attention was led by researchers from the University of Barcelona.

According to them, there was a presence of the new coronavirus in frozen samples, collected in Spain, since January 15, 2020 (41 days before the first official notification of a contagion in the country) and since March 12, 2019 (nine months before the first case reported in China).

But,how a virus with the potential to cause a pandemic could have circulated without attracting attention or create an explosion of cases, as happened in Wuhan?

Experts cite at least five hypotheses.

One is that patients may have received incorrect or incomplete diagnoses of respiratory diseases, something that would have contributed to the initial spread of the disease.

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Experts believe that the first outbreak of the new coronavirus emerged in Wuhan.

Another is that the virus had not spread with enough force to cause an outbreak.

There are also two possibilities problem analysis– Possible sample contamination or a false-positive result due to genetic similarity to other respiratory viruses or failure of the test kit.

Finally, there are those who speak of a virus waiting to be activated.

Tom Jefferson, an epidemiologist linked to the Center for Evidence-Based Medicine at Oxford University, told the British newspaper The Telegraph that there is a growing body of evidence that the SARS-CoV-2 was widespread before it emerged in Asia.

« Perhaps we are seeing a latent virus that has been activated by environmental conditions, » he said.

For Fernando Spilki, president of the Brazilian Society of Virology, it is necessary to wait for more studies on the subject before drawing conclusions about the incidence of the virus months before the known origin of the pandemic, in December.

« All these results should be evaluated with caution. The characteristic of SARS-CoV-2 of generating cases of high severity and with a relatively high lethality in the population makes this virus unlikely to circulate in a region without evidence of clinical cases« 

The findings in Brazil

In Brazil, a team led by researchers from the Federal University of Santa Catarina (UFSC) analyzed six 200 ml samples of frozen raw wastewater, collected in Florianópolis from October 30, 2019 to March 4, 2020.

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Recent research indicates that the new coronavirus is also present in the stool of patients.

The result of the investigation was reflected in an article, which has not yet been submitted to the review of other academics, in which they point out that the presence of the virus was detected from November 27.

In that sample, according to them, there were 100,000 copies of the virus genome per liter of wastewater, a tenth of that identified in the March 4 sample. Santa Catarina officially registered the first two cases on March 12, in Florianópolis.

According to the researchers, the virus was identified in the wastewater samples using the RT-PCR test, capable of detecting the presence of SARS-CoV-2 from 24 hours after contamination of the patient. This test basically converts the RNA of the virus (genetic material) into DNA to identify its presence or not in the sample examined.

« This shows that SARS-CoV-2 ccirculated in the community months before the first case was reported« in the American continent, write the authors of the article.

Biologist Gislaine Fongaro, research leader and professor in the UFSC department of microbiology, immunology and parasitology, said that the first results aroused skepticism in the team.

For this reason, they contacted other departments of the university to collect and repeat all the tests with various viral markers (which serves to prevent other similar viruses from confusing detection).

According to her, the presence of the virus months before the official registration can be explained, for example, by the fact that people may or may not have gotten sick or attributed the symptoms to other diseases.

But, according to Fongaro, only future studies can explain how the virus ended in the Florianopolis sewer in November.

Genetic sequencing of the virus found in wastewater could, for example, be compared with other similar tests done around the world to estimate the precise date of origin of SARS-CoV-2.

When did the pandemic really start?

The official chronology of the covid-19 pandemic has changed over time because much remains to be discovered about the disease, how it spreads, and mainly its origin.

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The first outbreak of the new coronavirus is estimated to be related to the wet markets in Wuhan, where live and dead wild animals are sold.

It is still unclear how and when the SARS-CoV-2 virus began infecting the human species.

There is consensus among scientists that the first outbreak occurred in a Wuhan market who sold dead and alive wild animals. But researchers don’t know if the virus appeared there or « took advantage » of that place to spread from person to person.

« If you ask me what is most likely, I tell you that the virus comes from markets that sell wild animals, » Yuen Kwok-yung, a microbiologist at the University of Hong Kong, told the BBC.

The gaps remain. The first cases of covid-19 were officially reported in late December, but a study by doctors in Wuhan, published in January by The Lancet medical journal, found that the first known case of covid-19 in a human it had happened weeks before.

The patient was an elderly man from Wuhan who had no connection to the market.

The timeline of the pandemic in Brazil may also change.

The first official diagnosis in the country occurred on February 26. It was a 61-year-old businessman, a resident of Sao Paulo, who was returning from a trip to Italy, where a large number of cases were beginning to emerge.

But the analyzes carried out by researchers from the Oswaldo Cruz Foundation (Fiocruz) reveal that in Brazil there was at least one case of SARS-Cov-2 one month before, between January 19 and 25.

According to that study, the virus would also have circulated among the country’s inhabitants a month earlier than estimated by the federal government.

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There is evidence that the first contagion in Brazil occurred a month before the disease was officially detected.

To reach these conclusions, Fiocruz relied mainly on two elements: the retrospective analysis of samples collected from patients in previous months and the comparison between the number of people with respiratory diseases without apparent cause detected in 2020 with those of previous years.

But how, then, can these gaps be solved? Some experts advocate doing research using old school methods.

« These outbreaks should be properly investigated with people on the ground, one by one. You must do what John Snow did. You question people and start building hypotheses that fit the facts, and not the other way around, « said epidemiologist Tom Jefferson, who is linked to Oxford University, in an interview with The Telegraph.

Dr. John Snow (1813-1858) is considered one of the founders of modern epidemiology. In 1854, he decided to investigate on the spot a cholera outbreak then hitting London. The disease had killed tens of thousands of people in that city in the past two decades.

Snow did not accept the most widespread theory at the time, according to which the contagion was due to « rotten and stale air ».

In his famous data analysis, Snow interviewed city residents and pioneered a case-by-case mapping and ended up determining that the cause of the outbreak was actually a public source of waste-contaminated water.

The discovery sparked a revolution in research on the spread of disease.

Is it possible for SARS-CoV-2 to spread through wastewater?

The presence of the new coronavirus in the faeces increases the possibility of contagion through the wastewater.

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Untreated sewage can discharge a significant viral load into rivers.

In 2003, during the pandemic of another SARS-CoV virus, the infection of hundreds of residents in the same building in Hong Kong was attributed to leaks in the sewer pipe.

In the current pandemic, still there is no evidence that this has occurred or that transmission of SARS-CoV-2 is viable after being excreted in the faeces.

There is also no official recommendation on the use of bleach to contain contagion through sewage, as has been circulating in WhatsApp groups. Pollution occurs mainly through the respiratory tract.

Studies indicate that the wastewater treatment system can eliminate the presence of the virus, but the precarious health situation in countries like Brazil can lead to the discharge of a large viral load in rivers without adequate treatment.

According to data from the National Sanitation Information System, corresponding to 2018, only 46% of the wastewater generated in Brazil is properly treated.

The lack of sanitation in that country generates more than 300 thousand hospital admissions per year, but It is not yet possible to state that the presence of coronaviruses in wastewater represents a health risk of the population.

SARS-CoV-2 can appear in the stool of up to half of covid-19 patients, including those who have had diarrhea, a symptom reported by 1 in 5 patients.

Some studies indicate that the virus generally appears in the stool about a week after symptoms and can remain for another five weeks after the patient recovers.

According to some research, the method of monitoring the presence of the virus in a city’s sewer system allows alerting on the existence of an outbreak between seven and ten days before the official registration.

One of the advantages of this approach is that it also allows monitoring of patients without symptoms or who have not been diagnosed.

In Belo Horizonte, for example, a pilot project of the National Water Agency (ANA) analyzes samples of wastewater and indicates that the number of infected people may be 20 times greater than that of officially confirmed cases.

What other things can be analyzed in the sewers?

The career of « wastewater epidemiologist », which has spanned the past two decades around the world, has expanded in recent years.

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While clinical studies allow the study of particular cases, the analysis of sewage serves for the study of communities as a whole.

One of the main functions of this professional is to discover, for example, how you can compare the level of illegal drug use estimated through traditional methods, such as questionnaires, with the most direct evidence found in sewerage systems. And thus verify if there is an under-registration, among other information.

This technique is not aimed at obtaining information on specific individuals but rather on localities, which would alert authorities to the effectiveness of public health campaigns and services in a given region, as well as whether police resources are being used appropriately. .

In addition to drug use, this type of particle analysis found in sewers can be used to analyze habits related to food and medicine consumption.

A laboratory at the University of Queensland, Australia, for example, conducted collections at wastewater treatment plants across the country to analyze eating and drug use habits in different communities.

The result? Overall, the researchers found that the richer the community, the healthier its diet.

In the highest socioeconomic strata, the consumption of fiber, citrus and caffeine was higher. In the lower ones, a significant use of prescription drugs was found.

On the other hand, the use of antibiotics is fairly evenly distributed among different socioeconomic groups, indicating that the government-subsidized health system is doing its job.


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