Complex sentence: It was converted to Ruttonjee Hospital, a general hospital, in 1991 not only because the number of patients suffering from tuberculosis had decreased, but also because they can increasingly be healed by out-patient chemotherapy.
Split into simpler sentences: It was converted to Ruttonjee Hospital, a general hospital, in 1991 as the number of patient suffering from tuberculosis had been decreased. It is also because the patients can be healed by out-patient chemotherapy.