Former President Bill Clinton was still in a California hospital as of Friday evening for treatment of a blood infection.

Doctors say the infection was caused by a urinary tract infection, which is not very common in men.

Clinton’s doctor told CNN Friday that “after two days of treatment, his white blood cell count is trending down and is responding to antibiotics well,” adding they “hope to have him go home soon.”

Dr. Matthew Foley, vice chair of Emergency Medicine at North Shore University Hospital, says the body will often naturally heal itself of a UTI, but that it can also go unnoticed in men.

“It can become more significant or more extensive in men without them noticing,” Foley says. “So, it’ll get to the point in men where it’s progressed, especially in older men, to alter mental status. That can sometimes be the first sign.”

He says if that happens, it is time to head to the hospital for treatment because if not, it can worse and get into the bloodstream.

Doctors say it’s often treated with hydration and antibiotics, but it depends on the person, their immune system and how vulnerable they are to bacterial infections.