It may be a respiratory virus, but studies have repeatedly found traces of Covid-19 in the faeces of infected patients. Using this to their advantage, scientists are sampling untreated sewage from wastewater plants in an effort to track the virus. Hannah Devlin speaks to Andrew Singer about how what we flush down the toilet can help detect emerging outbreaks – days before patients begin presenting with symptoms. Help support our independent journalism at theguardian.com/sciencepod