How did anne franks father escape the concertration camp?

The 15-year-old girl and her father were deported from the Netherlands to Auschwitz in September 1944. Several weeks later, in the face of the advancing Soviet army, Anne was evacuated along with many other Jews to the Bergen-Belsen camp, where she died of typhus in March 1945. Her father came down with typhus in Auschwitz and was sent to the camp hospital to recover. He was one of thousands of sick and feeble Jews who were left behind when the Germans abandoned the camp in January 1945, shortly before it was overrun by the Soviets. He died in Switzerland in 1980.