The CDC’s national wastewater surveillance system, which tracks SARS-CoV-2 levels in sewage across the country, shows most of the United States sitting at very low to low COVID-19 activity heading into late August, but two states stand out sharply from that pattern. Texas and Mississippi both registered high viral activity levels in wastewater for the week ending August 15, 2026, according to data CDC updated August 20. California, the nation’s most populous state, sits one tier lower at moderate, a reading drawn from 78 monitoring sites, by far the most robust dataset of any state in the moderate or high category, which lends it particular weight given the sheer number of people it represents.
Wastewater surveillance works by testing sewage for viral genetic material, which allows health officials to detect a rise in community transmission before people get sick enough to seek medical care, and it can pick up infections in people who never develop symptoms at all. CDC assigns each state a viral activity level, ranging from very low to very high, based on the concentration of virus detected relative to that pathogen’s own historical range. For COVID-19, a level below 2.6 is classified very low, while anything above 11.6 is very high.
Texas recorded the highest reading in the country, at 11.21, based on data from 40 monitoring sites across the state. Mississippi followed close behind at 9.46, though its reading is drawn from only two reporting sites, a much thinner sample that warrants some caution in interpretation. California’s moderate reading of 5.25, by contrast, carries more statistical weight than either of those two states given its far larger site count, and with a population of roughly 39 million, even a moderate classification there could represent more total infections than the high readings in smaller states combined. A handful of other locations, including Hawaii, Guam, and the U.S. Virgin Islands, also registered moderate activity levels, though each with far fewer reporting sites than California.
The rest of the country looks markedly different. The majority of states, including New York, Ohio, Pennsylvania, and most of the Midwest and Northeast, sit at very low activity levels, several of them at or near the floor of CDC’s measurement scale.
Wastewater monitoring offers an early warning signal, often surfacing well before hospitalization or clinical testing data catch up, which makes it a useful complement to other surveillance tools heading into fall. CDC updates the dataset every Friday with the prior week’s figures, and recent weeks may still be revised as more sites report in.
Sources and further reading:
Wastewater Data for Respiratory Viruses — CDC, National Wastewater Surveillance System, data through August 15, 2026
This article was researched and sourced by Global Biodefense editors and reported with Claude AI assistance for drafting and editing