How spying on sewage could save lives

If, as the saying goes, you are what you eat, then it stands to reason you also excrete what you are. Vladimir Putin apparently appreciates this fact. When he relieves himself on trips abroad, it is reported that a modern-day “groom of the stool” discreetly retrieves the dictator’s waste for subsequent disposal, lest it fall into the hands of hostile intelligence agencies, whose analysis might reveal compromising signs of ill-health.

Mr Putin is right to pay attention to poo. The analysis of a city’s wastewater—the product, as some put it, of the “collective gut”—can provide all sorts of insights into the health and behaviour of its residents. Such surveillance is inclusive enough to sample all toilet users. It is also anonymous; billions of dollars cheaper than alternative sampling techniques; and flexible enough to monitor everything from drug use to diet and even mental health.