Polish health officials say former president and Nobel Peace Prize winner Lech Walesa could be in the hospital for as long as a week as doctors try to determine the cause of a high fever and gastric problems.

The 67-year-old Mr. Walesa entered the hospital in Gdansk Wednesday after feeling unwell the previous day. He is undergoing tests to determine the cause of his illness, which doctors say is not related to a pre-existing heart condition. They also say Mr. Walesa is not infected with the E. coli bacteria that has killed 30 people in Europe.

Mr. Walesa was the founder of the Solidarity anti-communist movement in the 1980s, which led to the peaceful end of communism in Poland in 1989.

He was awarded the Nobel peace prize in 1983 and became Poland's first democratically-elected president in 1990. Mr. Walesa has since traveled the world to lecture about Poland's peaceful transition to democracy.