With CMMB, Catena volunteered to help the Roman Catholic Diocese of El Obeid establish the Mother of Mercy Hospital in the Nuba Mountains, which was built in 2007 and first launched its operations in March 2008. The region has been an area of active conflict since early 2011, and Catena is the only surgeon for the surrounding population of 750,000 people. The hospital's catchment area covers roughly one third of South Kordofan, equivalent in size to the entire country of Austria. Patients frequently travel by foot or hitchhiking for up to a week to reach the Mother of Mercy Hospital. At any one time it has between 300–450 in-patients. Patients visit the hospital for ailments varying from fractures, diarrhea, thyroid disease and cancer but also an increasing number of victims of bombing attacks or malnourishment spurred on by the war. Humanitarian aid is restricted, a ban which Catena defies. Very few NGOs still operate due to the Khartoum government's blockade. Since 2012 aid is not expressly forbidden, but it is in practice impossible as volunteers may not travel into the region. German Emergency Doctors and Samaritan's Purse had a presence as of 2013, but employed no trained medical doctors in the region. Limited by his surroundings, Catena sometimes uses decades-old treatments, and earns $350 a month while being on call 24/7. He engages the local community in the work as nurses and other assistive personnel, including through trainings in Kenya, South Sudan, and Uganda. The Mother of Mercy Hospital was subject to bombings by Sukhoi Su-24fighter jets operated by the Sudanese Air Force in May 2014, although at the time no one was injured. In preparation in case of bombings the compound now has a number of foxholes where patients and staff can flee for the duration. Catena credits his Catholic faith for his work, and says he is inspired by St. Francis of Assisi. He is known by locals as "Dr. Tom" and is widely respected by the population. A local Muslim chief said of Catena, "He's Jesus Christ", owing to Catena constantly healing the sick, helping the lame walk, and making the blind see. Since 2016, Catena has been serving on the selection committee for the annual GersonL'Chaim Prize for Outstanding Christian Medical Mission Service. In 2018, he was appointed chair of the Aurora Humanitarian Initiative, a position he holds in addition to his activities in Sudan.
Recognition
2020 - Gerson L’Chaim Prize for "outstanding Christian medical missionary service" from Florida-based nonprofit African Mission Healthcare; the L’Chaim Prize is a $500,000 reward sponsored by Jewish philanthropists Rabbi Erica and Mark Gerson
2018 – Catholics in Media Associates Social Justice Award
2017 – Aurora Prize for Awakening Humanity; besides receiving a grant in the sum of $100,000, Catena chose the following three organizations to share the prize's $1,000,000 award to continue their work: