(NEXSTAR) – Warning signs that could signal a rise in COVID infections are appearing in parts of the U.S.

Wastewater testing, which can help detect the spread of a COVID in a community, has shown a significant uptick of the virus in several states. Testing sites in Montana and Florida are reporting “very high” levels of COVID, the Centers for Disease Control and Prevention reports. Levels are “high” in wastewater across Alaska, California, Connecticut, Georgia, Maryland and New Mexico.

Emergency room visits related to COVID-19 are also on the rise, the CDC says, spiking 12.6% in one week. The biggest jumps were seen last week in Delaware, Iowa, Illinois, Indiana, Nebraska, New Jersey, Rhode Island, Vermont, Virginia and West Virginia.

Even with the recent increases, however, hospitalizations for COVID-19 remain very low nationwide. Only 0.6% of all emergency department visits were diagnosed as COVID cases last week.

The CDC also reports a 1% increase in positive tests, but with the proliferation of at-home COVID testing, positive cases often go unreported.

The uptick in cases may be driven by the new dominant subvariants, like FLiRT and KP.3. While COVID vaccines are still very effective against these strains, it may be a while since you’ve gotten a booster, leaving you more susceptible.

“If everybody’s getting vaccinated in November and December and then everyone is getting sick in December and January, the population is all becoming susceptible around the same time in the summer,” Ilan Rubin, a research fellow at the Harvard T.H. Chan School of Public Health, told TIME.

The travel and socializing that comes with summer may also increase your exposure.