The 75-year-old was admitted to the University of California Irvine Medical Center on Tuesday evening "for a non-COVID-19 infection," Clinton spokesman Angel Urena said on Twitter.
"He is on the mend, in good spirits, and incredibly thankful to the doctors, nurses and staff providing him with excellent care," Urena wrote. The spokesman added to Reuters: "He’s up and about, joking and charming the hospital staff."
Clinton went to the hospital after feeling fatigued and was diagnosed with an infection of the bloodstream that doctors believe started as a urinary tract infection, CNN reported, citing his doctors.
The former president's physicians, Alpesh Amin and Lisa Bardack, said he was "admitted to the hospital for close monitoring and administered IV antibiotics and fluids."
"He remains at the hospital for continuous monitoring," they said in a statement. "After two days of treatment, his white blood cell count is trending down and he is responding to antibiotics well."
They added: "We hope to have him go home soon."