Wastewater-Based Molecular Epidemiology of SARS-CoV-2 and Influenza Viruses in Southeastern Brazil
This study demonstrates that wastewater-based molecular epidemiology using RT-qPCR and dPCR effectively complements clinical surveillance by tracking the circulation and seasonal dynamics of SARS-CoV-2 and Influenza A and B viruses in São José do Rio Preto, Brazil, while revealing significant correlations between viral loads and sewage temperature.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Viruses that make us cough, sneeze, and fever often leave a hidden trail long before a doctor sees a patient. While we typically think of respiratory illnesses like the flu or the virus that causes COVID-19 as things that travel only through the air, these pathogens also find their way into our digestive systems and exit our bodies in waste. This means that the water flowing out of our homes and into the sewer system carries a microscopic record of who is sick in a community. By studying this wastewater, scientists can get a broad, population-wide view of disease spread that does not rely on people seeking medical care or getting tested. This approach, known as wastewater-based epidemiology, turns the sewage network into a massive, passive surveillance system, offering an early warning signal for outbreaks that might otherwise go unnoticed until they are already widespread.
In southeastern Brazil, a team of researchers decided to put this concept to the test by looking for two major respiratory viruses in the raw sewage of São José do Rio Preto. Over the course of two years, they collected weekly samples from the city's main sewage treatment plant, which handles all the wastewater generated by nearly half a million residents. Their goal was to see if they could find genetic traces of the influenza A virus and the virus that causes COVID-19, and to understand how the presence of these viruses in the water changed over time and with the weather. The team used highly sensitive laboratory techniques to concentrate the tiny viral particles from large volumes of water and then searched for their specific genetic fingerprints. To ensure their results were accurate, they also measured the amount of pepper mild mottle virus in the samples, a common plant virus found in human feces that serves as a reliable marker for how much human waste is actually present in the sewage.
The researchers found that both viruses were indeed circulating in the community, leaving their mark in the sewage even when clinical cases were low. They detected genetic material from the influenza A virus in nearly a quarter of the samples and from the SARS-CoV-2 virus in about one in six samples. Notably, they did not find any traces of influenza B virus. When they tracked the numbers over time, two distinct patterns emerged. The influenza A virus showed up in two clear waves, peaking in May and again in December of 2023, with the highest concentrations reaching millions of viral copies per liter of water. In contrast, the SARS-CoV-2 virus appeared in a single, sharp peak during January 2023. These findings aligned well with official health records from the city, which showed similar spikes in reported cases during those same periods, confirming that the sewage was accurately reflecting the health of the population.
Beyond simply counting the viruses, the team investigated how the physical environment of the sewage might influence what they found. They discovered a surprising link between the temperature of the wastewater and the presence of the viruses. Warmer sewage temperatures were associated with a higher number of samples testing positive for the SARS-CoV-2 virus and with higher concentrations of the influenza A virus. This suggests that environmental conditions within the sewer system itself might play a role in how long these viruses survive or how easily they are detected. While the study did not find strong connections between viral levels and other factors like the speed of the water flow or its acidity, the temperature relationship stood out as a significant clue. The study also confirmed that the methods used were robust, with the lab successfully recovering a high percentage of the viruses they added to test samples and finding no evidence that chemicals in the sewage were blocking their detection tools.
This work demonstrates that monitoring the water leaving our cities is a powerful way to keep tabs on respiratory diseases. The study showed that even after the peak of the global pandemic, the SARS-CoV-2 virus continued to circulate quietly in the community, and that influenza viruses followed their own seasonal rhythms, appearing most frequently in the cooler months. By combining these environmental signals with traditional health data, public health officials can gain a more complete picture of disease dynamics. The research suggests that wastewater surveillance is not just a tool for the past but a vital, ongoing strategy for the future, capable of revealing the invisible movements of viruses through a city and helping communities stay one step ahead of potential outbreaks.
Drowning in papers in your field?
Get daily digests of the most novel papers matching your research keywords — with technical summaries, in your language.