Paula Garcia-Sanchez ^1,2,3* David Romero-Trancón ² Iker Falces Romero ^4,5 Paula Navarro ⁴ Guillermo Ruiz-Carrascoso ^4,5 David Carmena ^5,6 María Casares Jiménez ^5,7 Antonio Rivero-Juarez ^5,7 Laura Moya ⁸ Jaume Rodón ⁸ Fernando Esperón ⁹ Belén Perez-Hernando ⁵ Rocío Sánchez-León ^10,2 Jara Hurtado-Gallego ^2,5 Sonia Alcolea ^{11,12,13,2,3,5} Talia Sainz ^11,14,15,2,5 Cristina Calvo ^11,14,15,2,5 Ana Mendez-Echevarria ^{11,14,15,16,2,5}

• ¹ Pediatric Emergency Department, University Hospital La Paz, La Paz, Madrid, Spain
• ² University Hospital La Paz Research Institute (IdiPAZ), Madrid, Madrid, Spain
• ³ Doctoral Program in Medicine and Surgery, Autonomous University of Madrid, Madrid, Madrid, Spain
• ⁴ Clinical Microbiology Department, University Hospital La Paz, La Paz, Madrid, Spain
• ⁵ Center for Biomedical Research in Infectious Diseases, Carlos III Health Institute (ISCIII), Madrid, Madrid Community, Spain
• ⁶ National Microbiology Center, Carlos III Health Institute (ISCIII), Madrid, Madrid, Spain
• ⁷ Infectious Diseases Unit, Reina Sofia University Hospital, Cordoba, Spain
• ⁸ Idexx Laboratories, Barcelona, Spain
• ⁹ Veterinary Faculty, European University of Madrid, Villaviciosa de Odón, Madrid, Spain
• ¹⁰ Doctoral Program in Microbiology, Autonomous University of Madrid, Madrid, Madrid, Spain
• ¹¹ Pediatric Infectious and Tropical Diseases Department, University Hospital La Paz, La Paz, Madrid, Spain
• ¹² Pediatrics Department, Hospital Universitario Severo Ochoa, Madrid, Madrid, Spain
• ¹³ Puerta de Hierro Health Research Institute (IDIPHISA), Majadahonda, Madrid, Spain
• ¹⁴ Pediatric Department, Autonomous University of Madrid, Madrid, Madrid, Spain
• ¹⁵ Translational Research Network in Pediatric Infectious Diseases, Madrid, Spain
• ¹⁶ ERN TransplantChild, Madrid, Spain

Introduction: Although pets provide several social-emotional benefits for children, the risk of zoonosis must be considered among immunocompromised individuals.Methods: A prospective study was conducted in a tertiary hospital including immunocompromised patients younger than 20 years owning dogs and/or cats.Colonization and/or infection was evaluated by stool studies, bacterial swabs, blood polymerase chain reaction and serological studies in both patients and their pets, to evaluate potential zoonotic transmission occurrence.We included 74 patients and their 92 pets (63 dogs, 29 cats). Up to 44.6% of the patients and 31.5% of the pets had at least 1 positive result. Up to 18.4% of pets' fecal samples were positive (bacteria, parasites or hepatitis E virus). No helminths were observed despite the high frequency of incorrect intestinal deworming practices. Among children, gastrointestinal microorganisms were found in 37.3% (primarily Clostridium difficile). Colonization by Staphylococcus pseudintermedius was common among pets (8%) but not among children (0.0%). No shared colonization between owners and pets was observed, except in one case (Blastocystis in both patient and pet feces). Among patients, serologies were positive for Strongyloides stercoralis (14.8%), Toxocara canis (3.2%), Bartonella henselae (19.1%) and hepatitis E (5.6%). Serology was positive for Rickettsia spp. (22.6%) and Babesia spp. (6.5%) in dogs and for Leishmania spp. (14.3%) and Toxoplasma spp. (14.3%) in cats.Conclusions: Exposure to zoonotic agents was detected in both patients and pets; however, shared colonization events were almost nonexistent. In our cohort, dogs and cats do not appear to entail high zoonosis transmission risk for immunocompromised patients.