Recently, New York City health officials reported finding samples of the poliovirus, which causes polio, in the county’s sewage. A similar alert also occurred in London and Jerusalem. The finding immediately motivated public health actions, especially the intensification of vaccination of the population of these places. At first, the fact that the virus was detected by monitoring sewers may seem strange, but it is not. This is an important epidemiological surveillance strategy for several diseases.
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— Sewage monitoring is an important public health action because it makes it possible to detect the disease before people start to get sick. This strengthens the sanitation policy — completes the researcher José Paulo Gagliardi Leite, from the Laboratory of Comparative and Environmental Virology at the Oswaldo Cruz Institute (IOC/Fiocruz).
The last time wild poliovirus was detected in Brazil was in 2014, at Viracopos airport, as a result of surveillance work carried out by Cetesb – Companhia Ambiental do Estado de São Paulo, which systematically monitors poliovirus and cholera in sewage from ports, airports and bus stations in the metropolitan region of São Paulo. Although these diseases are eliminated from Brazil, there are places where they still exist. This means that they can be brought by tourists. Monitoring these locations allows you to control this.
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— This monitoring is important to know the silent circulation of these viruses. We were able to detect it before symptomatic cases of the disease appear and thus initiate preventive measures — evaluates virologist Edson Elias, head of the Enterovirus Laboratory at the Oswaldo Cruz Institute (IOC/Fiocruz).
This monitoring is particularly important at this time, given the low vaccination rate. The percentage of immunization against polio has not reached the 95% desired by the Ministry of Health since 2015. Last year, it reached only 70% of children.
— Brazil has low vaccination coverage, so we are at a very high risk of polio reintroduction. A single case already represents a very big alert — explains the biologist Mikaela Renata Funada Barbosa, manager of the Division of Microbiology and Parasitology at Cetesb.
Sewage monitoring is also carried out by collecting samples at sewage treatment plants (ETEs). According to Barbosa, there will be an increase in disease monitoring points for some neighborhoods in the city of São Paulo and municipalities in the interior.
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Since the beginning of the Covid-19 pandemic, the strategy has also been used by several cities, including São Paulo, Niterói (RJ) and Belo Horizonte (MG), to detect the presence of Sars-CoV-2 in the sewage of cities.
— We can not only detect, but also quantify the presence of the virus in cities and neighborhoods. These data help to identify trends and guide public policies, regardless of clinical data — says Cesar Mota, associate professor at the Federal University of Minas Gerais (UFMG) and coordinator of the Covid Sewage Monitoring Network, a pilot project created to detect and quantify the new coronavirus in sewage samples in the cities of Belo Horizonte and Contagem.
For example, the monitoring of Confins International Airport, in Belo Horizonte, can guide decisions on mask use and hygiene. On the other hand, the monitoring of a nursing home in Santa Casa de Belo Horizonte may indicate the need for mass testing actions. In addition, the increase in the amount of virus in the sewage precedes by a few days the increase in people with symptoms and by a few weeks, the increase in hospitalizations, which can serve as a warning to the health system of the municipalities.
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Today, the network has already expanded to five other capitals – Fortaleza (CE), Recife (PE), Brasília (DF), Rio de Janeiro (RJ) and Curitiba (PR) – and it was so successful that the next step is to create a National Epidemiological Surveillance Program based on sewage. According to Mota, this planning is already happening with the Ministry of Health and the idea is to go beyond Covid-19 and include other infectious diseases, such as viruses, arboviruses and germs with antibiotic resistance.
The ideal way to monitor sewage diseases is through the analysis of the material that arrives at sewage treatment plants (ETEs), because if something is found, it is possible to know which neighborhoods the virus is circulating in. and initiate targeted actions.
— For any study with sewage, it is necessary that the network cover at least 90% of the population. A city with well-dimensioned sewage networks by neighborhoods, which go to a specific treatment plant, makes it possible to map the spread of parasites and initiate preventive public health actions. Without it, it is not possible to monitor — points out Leite.
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However, this would make this type of surveillance impossible in most Brazilian cities. Data from the 14th edition of the Sanitation Ranking show that only 50% of the country’s sewage volume receives treatment. Therefore, the researchers found other ways.
In addition to the treatment plants, Cetesb monitors water from rivers that receive large amounts of untreated sewage. The Covid Sewage Monitoring Network also includes collections in rainwater channels, which receive raw sewage from the population. Mota explains that knowing the topography of the place, it is possible to infer which population is contributing with the sewage that goes to these channels.
— We have been doing this follow-up and it has worked in situations of greater precariousness of network coverage — says Mota.
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The frequency of collection of material varies according to each project, and can be weekly or fortnightly. A professional from the laboratory or sanitation company collects the sample, which varies between one to two liters of sewage, at each point. This material is refrigerated and taken to the laboratory where the sample is concentrated and subjected to specific analyzes for each investigated pathogen.
The Covid-19 pandemic has made it clear that sewer disease monitoring can be an important public health tool and its potential continues to grow. In the United States, some cities are already using the sewage system to monitor the spread of monkeypox (monkeypox), for example.
Occasionally, Cetesb carries out environmental surveillance of other infectious agents, such as salmonella, hepatitis A, norovirus, rotavirus and enterovirus.
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— Any disease in which the causative agent is excreted in faeces or urine is likely to be monitored via sewage. The amount of epidemiological information present in the sewage is impressive and this has great potential, especially for a country like Brazil, which has a deficiency in clinical testing – concludes Mota.
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