( CNN ) Seventy years ago , Anne Frank died of typhus in a Nazi concentration camp at the age of 15 . Just two weeks after her supposed death on March 31 , 1945 , the Bergen-Belsen concentration camp where she had been imprisoned was liberated -- timing that showed how close the Jewish diarist had been to surviving the Holocaust . But new research released by the Anne Frank House shows that Anne and her older sister , Margot Frank , died at least a month earlier than previously thought . Researchers re-examined archives of the Red Cross , the International Training Service and the Bergen-Belsen Memorial , along with testimonies of survivors . They concluded that Anne and Margot probably did not survive to March 1945 -- contradicting the date of death which had previously been determined by Dutch authorities . In 1944 , Anne and seven others hiding in the Amsterdam secret annex were arrested and sent to the Auschwitz-Birkenau concentration camp . Anne Frank 's final entry . That same year , Anne and Margot were separated from their mother and sent away to work as slave labor at the Bergen-Belsen camp in Germany . Days at the camp were filled with terror and dread , witnesses said . The sisters stayed in a section of the overcrowded camp with no lighting , little water and no latrine . They slept on lice-ridden straw and violent storms shredded the tents , according to the researchers . Like the other prisoners , the sisters endured long hours at roll call . Her classmate , Nannette Blitz , recalled seeing Anne there in December 1944 : `` She was no more than a skeleton by then . She was wrapped in a blanket ; she could n't bear to wear her clothes anymore because they were crawling with lice . '' Listen to Anne Frank 's friends describe her concentration camp experience . As the Russians advanced further , the Bergen-Belsen concentration camp became even more crowded , bringing more disease . A deadly typhus outbreak caused thousands to die each day . Typhus is an infectious disease caused by lice that breaks out in places with poor hygiene . The disease causes high fever , chills and skin eruptions . `` Because of the lice infesting the bedstraw and her clothes , Anne was exposed to the main carrier of epidemic typhus for an extended period , '' museum researchers wrote . They concluded that it 's unlikely the sisters survived until March , because witnesses at the camp said the sisters both had symptoms before February 7 . `` Most deaths caused by typhus occur around twelve days after the first symptoms appear , '' wrote authors Erika Prins and Gertjan Broek . The exact dates of death for Anne and Margot remain unclear . Margot died before Anne . `` Anne never gave up hope , '' said Blitz , her friend . `` She was absolutely convinced she would survive . '' Her diary endures as one of the world 's most popular books . Read more about Anne Frank 's cousin , a keeper of her legacy .
Museum : The museum is located in the former home of William and Mary President Thomas Jefferson. Researchers re-examined archives and testimonies of survivors . Anne and older sister Margot Frank are believed to have died in February 1945 .