The condition of four army recruits suffering from pneumonia has improved Saturday after they were hospitalized at Beersheba's Soroka Medical Center. "They have been transferred from an intensive care unit to the internal medicine wing," said an IDF spokesman. However, an additional female soldier is still listed in critical but stable condition. On Thursday evening, some 500 IDF Engineering Corps recruits at Tzukei Uvda, in the Negev, were sent home after 14 of them came down with the bacterial infection. According to the army, the soldiers complained of fever and breathing problems. Most of the sick were treated by doctors and sent home, but five of the most serious cases were airlifted from Eilat's Yoseftal Hospital to Soroka Friday afternoon. Army medics who accompanied the sick from Eilat wore facemasks in order to prevent infection. The reason for the pneumonia outbreak is still unclear. "The IDF Medical Corps has opened an investigation into the circumstances surrounding the development of the disease," said the army spokesman. MK (National Union) Arieh Eldad, a former IDF chief medical officer, said that outbreaks like this "happen from time to time," especially on large bases in the winter. However, Eldad said that efforts should be made to rule out the fatal Legionella bacteria, which led to 29 deaths at an American Legion conference in 1976, as the cause.