I don’t know if miners really used caged birds to warn of oxygen depletion in mines or whether the idea is apocryphal. Since politics has prevailed over sensible science lately by curtailing COVID-19 test increases, we need a canary. At the University of Arizona recently, the canary of COVID testing turned out to be sewage.

What is not widely appreciated is that sewage pipes are a beautiful thing (as long as they work). A given pipe connects to a fixed number of residences and businesses, so researchers know how many people are using any given pipe. Sewage has been used for estimating illegal drug use in urban areas, determining the amount of estrogen excreted by birth control pill users, and other epidemiological surveys.

The University of Arizona tested all 311 students and dormitory workers for a dorm and found no active infections. Next, the University tested the sewage outflow from the dormitory for viral RNA. The presence of RNA means that a person has been infected in the past and developed antibodies for it. To their surprise, they found viral RNA in the sewage. Next, they tested all 311 people for viral RNA (which is a different test than the test for active infection) and found two students who were asymptomatic carriers. They were immediately quarantined, and their rooms disinfected.

What if the University had not gone ahead with inexpensive sewage testing (it tests 319 people at one time) and subsequent antibody testing? There would likely have been an outbreak not only of the immediate 311 people at the dorm, but with their families and communities at home as they travel back for holidays. The lack of sensible testing would have resulted in sickness and death.