How the CDC tests wastewater for Covid — and what it found in your state

(CNN) — New Covid-19 infections are no longer tracked or reported as closely as they were during the public health emergency. Instead, US officials now focus on testing the contents of Americans’ wastewater to keep tabs on the virus.

To identify virus levels and larger trends, the US Centers for Disease Control and Prevention relies on a large network of sampling sites at wastewater treatment facilities across the country. The monitoring network covers about 43% of the population.

The process doesn’t precisely count the numbers of cases, and readings can vary based on sewage flows at a particular location or the characteristics of a given variant at a point in time. But it provides an early warning about viral spread, CDC officials say. CNN is tracking these figures each week across the country and by state, and this page will update automatically as the agency releases new information.

Viral levels vary over time and by location. This table shows the trends by state, with rankings in ascending order by the severity of the viral activity during the most recent testing period.

Samples are taken from sampling sites around the United States that meet criteria to sufficiently anonymize the data. The sampling allows the CDC to see results from a large snapshot of the population, not just individuals who are in the health care system. Wastewater data also helps local public health agencies to track new Covid variants and other infectious diseases, such as RSV and mpox.

The agency reports the percentage change in viral levels at each location where data was collected during a 15-day period, with some densely populated states having more testing locations than others. This map shows those locations. Some sites saw an increase in activity, while others experienced a decrease.

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