The Centers for Disease Control and Prevention (CDC) stated last week that it’s investigating more than 100 mysterious hepatitis cases among children in at least 25 states. Most of the children have been hospitalized, and five deaths have been reported thus far.

The CDC has issued a health advisory to doctors and clinics so that they can be aware of symptoms and investigate them accordingly. In mid-April, the agency first said it was investigating nine cases in Alabama, meaning that last week’s announcement represents a significant uptick in cases.

While hepatitis can be caused by a myriad of issues, the most well-known causes are the viruses hepatitis A, B, and C—although the CDC and other medical agencies have ruled those out. Prolonged and heavy alcohol usage, drug overdoses, certain types of medication, and toxins can lead to liver inflammation, according to medical officials.

Signs and symptoms of hepatitis include the yellowing of the skin or whites of the eyes, nausea, vomiting, diarrhea, dark-colored urine, joint pain, a loss of appetite, fever, and fatigue, according to the Mayo Clinic.

Rajapakse noted that hepatitis symptoms are connected to “the liver not being able to do its job properly” and that a “symptom that you might notice is yellowing of the skin or the whites of the eyes. Sometimes the whites of the eyes are where it shows up first because it’s easier to pick up than in the skin.”

“Kids may also complain of abdominal pain, so especially in the right upper part of the abdomen, which is where the liver sits, they may have pain specifically there. But it can be anywhere in the abdomen. You might notice dark urine or light-colored stool,” she said.

Inside the United States, the CDC has confirmed that it’s investigating cases in Alabama, Arizona, California, Colorado, Delaware, Florida, Georgia, Idaho, Illinois, Indiana, Louisiana, Michigan, Minnesota, Missouri, North Carolina, North Dakota, Nebraska, New York, Ohio, Pennsylvania, Puerto Rico, Tennessee, Texas, Washington, and Wisconsin.