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According to a Bloomberg analysis of Centers for Disease Control and Prevention data, a wastewater network that monitors Covid-19 trends is warning that cases are once again on the rise in many parts of the United States.
More than a third of the CDC’s wastewater sample sites in the United States showed rising Covid-19 trends from March 1 to March 10, though reported cases remained near a recent low. The number of sites with rising signals of Covid-19 cases is nearly double what it was from February 1 to February 10, when the wave of omicron-variant cases was rapidly fading.
It’s unclear how many new infections the sewage signs represent, or whether they’ll be a new wave or just a brief blip on the way down from the last one. People are returning to work in many parts of the country, and mask regulations have been relaxed, both of which can increase transmission. Simultaneously, warmer weather allows people to spend more time outside, and many people have recently been infected, which may provide at least temporary protection against getting sick again – factors that would keep cases down.
“While wastewater levels are generally very low across the board, we are seeing an increase in sites reporting an increase,” Amy Kirby, the head of the CDC’s wastewater monitoring program, told Bloomberg in an email. “These bumps could simply be minor increases from very low levels to even lower levels. However, as prevention strategies in many states have changed in recent weeks, some communities may be seeing an increase in Covid-19 infections.”
Bloomberg examined data from over 530 sewage monitoring sites, focusing on the most recent data reported during the 10-day period between March 1 and March 10. Out of most sites, 59% showed falling Covid-19 trends, 5% were roughly stable, and 36% were rising. The rises and falls are calculated over a 15-day period.
During the period from February 1 to February 10, fewer sites had data. During that time, 80 percent of sites showed a decreasing trend, 5% remained stable, and 15% rose.
Wastewater samples cannot reveal how many people are infected with Covid-19. Instead, they count the amount of virus found in sewer water. A high concentration in a sample can indicate an increase in the number of infections, which can occur days before the cases are detected in tests.
Official case numbers derived from Covid tests have become increasingly untrustworthy. With more people having access to at-home tests, many infections, particularly mild ones, are going unreported. The proportion of unreported cases can be even higher in the midst of surges and when tests are scarce.
