Using wastewater as an early warning system for viral outbreaks

When you are flushing the toilet after doing number two, have you ever wondered what exactly you are sending out into the sewage and later on, the environment?

Alright, it might seem a bit bizarre to talk about your poop. But feces contain a large amount of information about diet, genes, and pathogens – pathogens are definitely a relevant topic this year.

By sequencing the genetic material of fecal samples from me, you, and all of your neighbors and analyzing what types of genomes are present, it is possible to monitor which viruses and how many are present in a population before illness symptoms appear. Since the coronavirus caused the lockdown of pretty much everything, an increased focus has been on how we can trace and break the chain of infections. Sampling urban sewage may give early warnings about rising cases in communities and allowing interventions to be made in time.

In Plymouth, UK, researchers detected a rise in the number of coronavirus fragments between samples taken in the summer and in September. The local health officials acted on this information and began to figure out where the infections were. Similar efforts are also being carried out around the world, e.g. in Australia, Denmark, and USA. One downside is that these studies are not able to pinpoint the exact household in which virus fragments were found, but the entire community could be ordered to get tested. So far, there is no evidence that coronavirus spreads through sewage.

Our ‘number two’s is not only useful for monitoring levels of coronavirus but other viral pathogens as well. Since the 1940s, actually. Several countries have kept a tab on the amount of poliovirus in sewage to prevent outbreaks or measuring the effects of vaccine initiatives. Swedish researchers reported in 2013 that they detected an early outbreak of hepatitis A and norovirus by repeatedly sampling wastewater.

How are we able to detect viral fragments so early? Most people with a viral infection that were transmitted enterically sheds large amounts of viruses in feces days before they start showing symptoms. Some of these viruses are even able to persist for a longer time in wastewater and they can even be transferred to food and start a new outbreak. Luckily, coronavirus does not have that ability. But still, if viruses can persist for a longer time, we still need to come up with new wastewater treatments that can effectively remove these pathogens.

Viruses are not the only thing present in our sewage as it is also possible to detect other genetic material such as antimicrobial resistance (AMR) genes. AMR is how pathogens learn to cope with many of our antimicrobial drugs, such as antibiotics. The rapid spread of AMR genes is also a significant threat to human health as deaths caused by multidrug resistant pathogens is estimated to reach 10 million deaths annually by 2050. One study highlighted the worldwide transmission of AMR genes by sequencing the DNA of toilet waste from international flights – critical important resistance genes were carried more by travelers from Asia than from Northern America. This illustrates how easy it is for pathogens to travel with the world with us. Global travel and trade did also drive the global spread of coronavirus this year.

Maybe this paints a scary picture, but thanks to the pandemic there have been an increased focus on how we can detect early outbreaks and stop them before they take over the world. If we can get rid of not only coronaviruses but also other viruses and AMR genes in the long-term, our health will certainly be better.

I wrote this post as an assignment for the course 22700 Effective Science Communication at DTU. But anyone can certainly enjoy it!