Background: Diarrhea frequently occurs after vascular organ transplantation, including kidney transplants. This may result from non-infectious factors, adverse effects of immunosuppressive medications, or infections caused by various pathogens, including viruses, bacteria, fungi, or parasites, for example, intestinal protozoan parasites such as Cryptosporidium spp., which are particularly dangerous for immunocompromised patients. Methods: This review is based on scientific articles sourced from validated databases such as PubMed, the National Center for Biotechnology Information (NCBI), ScienceDirect, and Google Scholar. The primary search was conducted on 12–13 July 2024, using the keywords ‘Cryptosporidium’ AND ‘cryptosporidiosis’ AND ‘kidney’ AND ‘transplant’ AND ‘adult’. Inclusion criteria encompassed human studies, case reports, peer-reviewed journal publications, review articles, and research articles in English. Exclusion criteria included studies not in English, gray literature (e.g., conference proceedings and abstracts), and data related to pediatric patients (under 18 years old) and HIV patients. Results: This systematic review and meta-analysis have highlighted an often-overlooked connection between Cryptosporidium spp. infections in adult kidney transplant recipients (KTR). Furthermore, it includes an analysis of the clinical presentation, diagnosis, and treatment of Cryptosporidium spp. infection in these patients, based on available case reports. Our study demonstrates that adult kidney transplant patients are at a significantly higher risk of acquiring Cryptosporidium spp. compared to healthy participants. Conclusions: Cryptosporidium spp. infections can be asymptomatic, making it essential to screen both symptomatic and asymptomatic kidney transplant recipients. The clinical presentation of cryptosporidiosis typically involves digestive symptoms and can be complicated by biliary tract involvement. In KTR patients presenting with diarrhea, it is crucial to not only test for Cryptosporidium spp. but also to rule out bacterial and viral etiologies, including infections such as C. difficile, C. colitis, Clostridium spp., and rotavirus. The diagnosis of Cryptosporidium spp. infections primarily relies on microscopic methods, which are known for their low sensitivity. Therefore, diagnostic approaches should include both direct methods and, where possible, molecular techniques. Based on the analyzed cases, the most effective treatment results were achieved with reduction in immunosuppression if possible (strong, very low) and nitazoxanide at a dose of 500 mg twice daily for 14 days. Considering the public health implications of our findings, the current epidemiological data underscore the need for further research to develop effective prevention and intervention strategies against cryptosporidiosis. Preventive measures, regular screening programs, and the treatment of Cryptosporidium spp. infections should be integrated into the clinical care of transplant patients. It is also important that patients are informed about environmental risk factors.
