Former US president Bill Clinton was recovering in a California hospital on Friday after several days of treatment reportedly for sepsis, a spokesman and media said.

Clinton, who led the United States from 1993 to 2001, was responding well at the UCI Medical Center in Irvine, south of Los Angeles, according to doctors.

Clinton spokesman Angel Urena said in a statement that the 75-year-old was admitted Tuesday evening for "a non-Covid-related infection."

"He is on the mend, in good spirits, and is incredibly thankful to the doctors, nurses and staff providing him with excellent care," Urena said late Thursday on Twitter.

The New York Times, citing an aide, said the former president had been hospitalized after a urological infection developed into sepsis.

Sepsis is an extreme bodily reaction to infection that affects 1.7 million people in America every year, according to the Centers for Disease Control and Prevention.

It kills 270,000 of those infected every year.

"Infections that lead to sepsis most often start in the lung, urinary tract, skin, or gastrointestinal tract," the CDC says on its website.

"Without timely treatment, sepsis can rapidly lead to tissue damage, organ failure, and death."

Photographs in US media showed his wife, former secretary of state and presidential candidate Hillary Clinton, visiting the hospital together with her aide Huma Abedin.

Urena released a statement from his doctors saying Clinton was admitted Tuesday "for close monitoring" and given antibiotics and fluids intravenously.

"After two days of treatment, his white blood cell count is trending down and he is responding to antibiotics well," they said Thursday.

"We hope to have him go home soon."

President Joe Biden said he had spoken to Clinton.

"I know you have been asking about president Clinton. I've been exchanging calls. He seems to be, God willing, doing well," he told reporters.

At the hospital on Friday there was a small visible police presence, and a large group of reporters.

Quadruple bypass

It was the latest health scare for America's 42nd president. In 2004, at age 58, he underwent a quadruple bypass operation after doctors found signs of extensive heart disease.

Six years later he had stents implanted in his coronary artery.

Known for a generous appetite that embraced fried foods, notably french fries, Clinton went clean and adopted a low-fat vegan diet.

Since then he has lost substantial weight.

In 2010 Clinton said his decision to go vegan was not a difficult one.

"Not when you have [had a] quadruple heart bypass and you want to live to be a grandfather," he explained.

The former governor of Arkansas was elected president at age 46, the third-youngest president in US history.

Garrulous, charming and well-read, he was a star for the Democratic Party and well-liked among fellow world leaders.

He remained popular even after his second term in the White House was marred by an affair with the young intern Monica Lewinsky that snowballed into his impeachment for lying in relation to an investigation.

But he stepped away from the limelight as his wife Hillary plunged into her own political career, winning election as a senator from New York and training her own sights on the presidency.

Despite his help, she lost the 2008 Democratic nomination to Barack Obama.

In 2016 she won the Democratic nomination for president but lost the election to Republican Donald Trump.

Criticism of Trump

Bill Clinton meanwhile gave speeches, led his nonprofit, the Clinton Foundation, and helped raise money for the Democrats as he slowly became just another of the now five ex-presidents still alive.

In 2004 he published an autobiography, and in 2011 another volume on how to revive the economy.

And since 2018 he has written two thrillers together with best-selling novelist James Patterson.

He has made brief returns to the political stage, helping his wife and others during election campaigns, and traveling to North Korea in 2009 to negotiate the freedom of two Americans held by the North Korean regime.

In January he and former presidents Obama, Jimmy Carter, and George W. Bush, came together to issue a strong statement condemning the January 6 attack on the US Capitol, directly accusing then-president Trump of inciting it and of spreading baseless lies.

But Clinton has also fought to avoid being pulled into the type of scandal that dogged his presidency.

His name surfaced in the sex trafficking scandal around late financier Jeffrey Epstein, with a former aide and a victim both saying Clinton had visited the Caribbean island where Epstein took underage women for sex parties.

Clinton knew Epstein but denied ever having visited the island.

His White House scandal also returned in September with the launch of mini series "Impeachment," covering the drama of his affair with Lewinsky and the political eruption that followed.