What can wastewater tell us about an outbreak?
Most outbreak data depends on people deciding they feel ill enough to get tested. Sewage does not. People shed traces of many infections in stool and urine, often before they feel sick, and sometimes without ever feeling sick. Testing at a treatment plant measures everyone connected to it at once. It is good at showing which way an outbreak is moving, and when it started to move. It can also find something nobody was looking for yet. It is poor at counting people, because turning a concentration into a number of cases needs too many guesses. And it says nothing about any individual. The sample is a mixture.
4 min read