A coronavirus patient in Northern California—who may have the first U.S. case not related to foreign travel or exposure to another known patient—reportedly wasn’t tested for days after they were admitted to a medical center. The Centers for Disease Control and Prevention said it doesn’t know how the person was exposed to the virus. There are fears it could mean the disease is now being transmitted in the U.S. by “community spread,” which would make it more difficult for authorities to evaluate sick patients. CNN reports the patient was transferred to UC Davis Medical Center from another Northern California hospital on Feb. 19 with a suspected viral infection, but wasn’t tested until Sunday because they “did not fit the existing CDC criteria” for suspected coronavirus—namely foreign travel or exposure to another known patient. Currently, the CDC says on its website that the virus is not spreading in the community in the U.S., but health officials have said they expect it will at some point in the near future.