Sewer tests are now providing a direct glimpse of just how many people are infected with the variant in some cities. Torres says a model he works with indicates that more than 200 people are infected with the variant just in his wastewater collection region, an exurb of 77,500 people.
Health officials in central Florida initially blamed their B.1.1.7 cases on visitors who tested positive, but the sewer tests in Altamonte indicate that the variant is spreading locally, too. Florida remains largely open for business, including theme parks, which are operating with the use of masks and physical distancing.
According to the US Centers for Disease Control and Prevention, only 611 cases of B.1.1.7 have been directly confirmed nationally via genetic sequencing of the viral samples collected in patient nose swabs, with many of the positives coming from California and Florida. Because only a small percentage of hospital swabs are ever analyzed for what form of the virus is present, the true number of B.1.1.7 cases is certainly much larger.
The US has less ability than some European countries to track variants of the virus because test swabs are not subjected to complete genomic sequencing as often, a situation some experts have likened to “flying blind” in the face of a changing pandemic.
According to the New York Times, as of January about 1.4 million people were testing positive for the coronavirus every seven days, but fewer than 3,000 of those clinical samples were being sequenced letter for letter, a step that’s usually necessary to see what mutations the virus has acquired.
Wastewater offers a chance to monitor the variant more widely, and at lower expense. A single liter of dirty water carries the remains of viruses shed into toilets by everyone who shares a sewer system, offering a readout on the health of thousands, even millions, of people.
Since last spring, some cities have used molecular tests on sewage as an early warning system, since the amount of coronavirus in sewage can predict how many people will turn up in hospitals a week to 10 days later. The reason sewage results go up or down before official case numbers do is that people seem to start shedding the virus into toilets a day or two before they feel ill, and it often takes even more time to receive a test result.