In 1854, he was summoned to Rome to take part in the definition of the dogma of the Immaculate Conception, and it is said that changes in the wording of the decree were due to his suggestions. His health entered into a steady decline and, on the advice of his physicians, traveled throughout Europe, Asia, and North America in search of a more hospitable climate. At the end of O'Connor's tenure, the diocese contained 77 churches, 86 priests, six religious congregations, one seminary, five institutions of higher education, two orphan asylums, one hospital, and a Catholic population of 50,000.