Over the past few days, there’s been a lot of talk about the fact that traces of SARS-CoV-2 were detected in the sewers of both Milan and Turin already, back in December of 2019. This data would therefore confirm that the coronavirus was present in Italy, well before so-called “Patient 1” of Codogno, which was most probably “Patient 1000 or higher”.

Hygienic health surveillance systems are very widespread and function very well. Unfortunately, they’re not systems that can predict what to look for, but detect known potential pathogens. However, in case of an epidemic, such as the one we’re all still experiencing, they can be very useful in analyzing the samples taken months before again, but they’re also very useful in the on-going search for the new pathogen.

This is exactly what’s been done by the Istituto Superiore di Sanità (ISS) and more precisely by the Reparto Qualità dell’Acqua e Salute (Italian Water Quality and Health Department).

In analyzing wastewater samples again, which were taken from October 2019 to February 2020, traces of SARS-CoV-2 were detected. In addition, researchers also analyzed samples taken in 2018, in order to compare the data and confirm the validity of the detection method used.

How is it that you can find traces of SARS-CoV-2 in feces?

In some cases, the symptoms of COVID-19 also “take the form” of diarrhea, so the virus, once it’s passed through the intestinal tract, can be expelled through the feces and then ends up in the sewer. Other viruses are detectable in feces and therefore in wastewater such as norovirus, poliovirus or measles virus, whose presence is usually detected in the winter season and serves as an additional indicator for monitoring the spread of these infections in the population.

Is sewage water dangerous? What about drinking water?

First of all, it should be pointed out that to date, traces of SARS-CoV-2 have been detected in household and hospital sewers. Here, “traces” means that the RNA of the virus has been detected and not the active virus, so there is no danger of transmission. However, virus in an infectious form has been detected in the feces of COVID-19 patients, but wastewater treatment is able to inactivate the virus, therefore rendering it harmless.

A very different situation could exist if sewage systems are not adequate. Indeed, in view of the studies carried out in 2003 during the SARS epidemic, a risk of fecal-oral transmission cannot be excluded in circumstances where wastewater contaminated the water, which was intended for human use. If these circumstances are rather remote (for example, in many European countries), they cannot be excluded in countries with less-advanced economic development.

Is it dangerous to drink tap water?

It’s not dangerous to drink tap water (refer to the Italian Ministry of Health’s point #24 — in Italian). The water that passes through purification plants undergoes a series of chemical-physical treatments that inactivate any pathogens present in water intended for domestic use. The controls are carried out very frequently, following international protocols developed, and various controlling bodies update them.

In conclusion, it’s very important to monitor viruses in general, and SARS-Cov-2 in particular, in samples taken regularly in sewers and at the entrance of purification plants as a tool — in order to detect and monitor virus circulation in a given territory at an early stage. However, standardization of sampling methods will become essential, as many variables such as the sampling period, possible rainfall levels, emission of industrial effluent all affect the positivity of the samples collected.

Given the imminent start of the summer tourist season, the Department of Environment and Health of the Istituto Superiore di Sanità (ISS) will launch a pilot study on priority sites identified within tourist resorts. Based on these results, the ISS will develop an integrated surveillance program throughout Italy, during the potentially most critical periods of this coming autumn season.

This post is also available in: Italiano

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