Henry Baker <hbaker1@pipeline.com> wrote:

Better to sample and test *sewage* at strategic branching locations in the sewer system, where the "mixing" has already taken place. (Yes, fecal matter does contain the virus.)

You would need an army (navy?) of small autonomous robots, each equipped with the ability to quickly do large numbers of virus tests. They'd also need access to a complete and accurate map of the city's sewer system, to the level of every individual household. (Do such maps even exist?) And they'd have to have some way to keep track of where they were, despite being in conductive pipes that neither GPS nor cell phone signals can penetrate. And they'd need a way to report their results. And once they did find and report that the virus is in a household, someone would still have to test every person in that household. I did come up with the idea a few years ago of sequencing all human DNA found in sewers, and cross-referencing it with a database of the DNA of fugitives. It's more feasible because there are far fewer fugitives than there are people infected with covid-19. "Hilarie Orman" <ho@alum.mit.edu> wrote:

It is being done. https://www.nature.com/articles/d41586-020-00973-x

Not the same thing. That article is about testing at the downstream end. That's very useful for determining if there's any of the virus in the city, and mildly useful for determining how much (if you assume the ratio of baths to flushes is roughly constant), but useless at learning which people are infected. By now, the answer to "is it in the city?" is almost certainly yes, whether the city is London or Timbuktu. But, assuming a technology that can quickly sequence and analyze *all* DNA, yottabytes of data, it would be useful for detecting new or known dangerous viruses, bacteria, parasites, etc. Probably a project for the last half of this century, if not the next one. The latter would be close to the level of technology necessary to make a complete backup of a living human brain. That may be the ultimate answer to viruses and the thousand natural shocks that flesh is heir to: Upload ourselves into computers. Then we need only fear *computer* viruses.