U.S. Republican presidential candidate Rick Santorum has dropped out of the race to win the White House, but says he will not stop working to defeat President Barack Obama.

Santorum made the announcement Tuesday in Gettysburg, Pennsylvania, just a day after his daughter, Bella, was released from a hospital where she was treated for a rare genetic condition called Trisomy 18 .

Santorum said her illness caused the family to think about his decision to leave the race. He said the family is looking forward to spending a lot more time with Bella.

He thanked his supporters and says he beat the odds to win millions of votes and 11 primaries.

Santorum, a former U.S. senator, pulled out of the race a week after losing three primaries to the frontrunner for the Republican nomination, Mitt Romney, a former governor of Massachusetts. Santorum had been looking towards the April 24 primary in his home state of Pennsylvania to give his sagging campaign a boost.

But even if he were to win Pennsylvania, Santorum would still be far behind Romney in the number of delegates needed to win the Republican Party nomination.

Romney congratulated Santorum on his campaign and called him an able and worthy competitor and an important voice on the nation.

Only two other candidates remain in the Republican race besides Romney — former House speaker Newt Gingrich and Texas Congressman Ron Paul.