Involuntarily passing of wind

Q: All praise be to Allah Alone, and peace and blessings be upon the Last of the Prophets. To proceed:The Permanent Committee for Scholarly Research and Ifta' has examined the question sent to His Eminence, the Grand Mufty, from his Eminence, the Manager of the Center of Da`wah and Guidance in Jeddah, which was referred to the Committee from the Secretariat General of the Council of Senior Scholars under no. 516, dated 28 Muharram 1416. The questioner asked the following question:A new Imam came to our Masjid (mosque) in Jeddah and told us that he had a disease in the large intestine that causes him to have constipation and to pass wind. (Part No. 4; Page No. 256) For this reason, he offers Wudu' (ablution) for every Salah after the start of its prescribed time, but sometimes when he leads congregational Salah, he passes wind. He is certain of releasing gas either by its sound or smell. He asks the following: 1-Is his ignorance of the ruling on passing wind affects the ruling on his Salah, as he used to think that involuntary expulsion of wind does not affect his Taharah (ritual purification).2-What is the ruling on offering Salah behind that Imam who is sure of passing wind?3-Is he obliged to tell the Ma'mums (people being led by an Imam in Prayer) about the Salahs which he performed without being Tahir (ritually pure)? What is the ruling if he was unaware of the number of Salahs which he offered while being ritually impure? How should he tell people about this?4- Do you advise him to continue as an Imam for that Masjid, given that his disease is not related to gas incontinence; rather, it is just a temporary condition in which he cannot resist passing wind? I hope you will attend to this issue and provide us with the relevant answer.