California is experiencing a resurgence in COVID-19 cases, with recent data indicating a sharp increase in the levels of coronavirus in wastewater across the state.

The levels are considered "very high" and have been since early July, according to the US Centers for Disease Control and Prevention.

For the seven-day period ending July 20, the wastewater levels were at 93 percent of the peak in the summer of 2022 and have already surpassed last summer's peak.

Overall, 37 states and the District of Columbia have rates of coronavirus in wastewater classified as "high" or "very high".

As of last weekend, California's current seven-day test-positivity rate was 13.8 percent, an increase of 2.3 percentage points from the previous week. That rate is approaching the highs of the summer of 2022, which peaked at 16.1 percent.

Elizabeth Hudson, regional chief of infectious disease at Kaiser Permanente Southern California, told the Los Angeles Times that more people are seeking outpatient treatment.

"The wastewater numbers are still headed up. So we're definitely seeing more and more cases," she said. "If you have cough-and-cold symptoms, at this point, living in Los Angeles, you should really think that they are COVID until proven otherwise."

There was an average of 286 COVID-19-positive patients in hospitals for the week ending July 20 in Los Angeles County. That number is about half of last summer's peak and one-quarter of the peak from summer 2022.

"This virus is still very, very new to humans, and the virus wants to live, and the way that it lives is by evading immunity," said Hudson.

Peter Chin-Hong, an infectious diseases expert at the University of California, San Francisco, told the Los Angeles Times that there is lot of COVID outside the hospital, and "almost everybody has it".

Other states with "high" or "very high" coronavirus levels in wastewater are Alaska, Colorado, Connecticut, Florida, Hawaii, Idaho, Missouri, Nevada, New Hampshire, New Mexico, Tennessee, Texas, Utah and Wyoming.

Agencies contributed to this story.