As Dartmouth students flowed into residence halls last week in staggered waves for a return to on-campus learning, researchers at nearby Dartmouth-Hitchcock Medical Center were watching what flowed out of the dorms for clues of coronavirus infection.

The researchers are examining human waste flushed by students and others in the Twin States. They are looking for genetic material, RNA, from the virus that causes COVID-19.

Because somewhere between 40% and 65% of people shed the novel coronavirus in their stool as much as a week before they get any COVID-19 symptoms, and many people with the virus never develop any symptoms, a positive test from a wastewater sample could serve as an early warning sign of the presence of the virus.