Opportunistic Intestinal Parasitic Infections in Corticosteroid-Treated Patients

Corticosteroid-induced immunosuppression creates a permissive environment for opportunistic intestinal parasitic infections (OIPIs), especially in endemic regions where latent or subclinical parasitic carriage is common. Yet, the interplay between corticosteroid exposure, parasitic ecology, and clinical outcomes remains insufficiently characterized. This study aimed to investigate the epidemiological and clinical characteristics of OIPIs in corticosteroid-treated patients by integrating findings from an original Egyptian case series with a systematic review of published global cases. A dual analytical approach was undertaken, combining newly characterized Egyptian corticosteroid-treated cases (ECS; n = 53) with a systematic review of global corticosteroid-associated parasitic cases (LRCS; 94 cases, 1975–2024). Clinical profiles, corticosteroid regimens, comorbidities, parasitic spectra, and outcomes were analyzed to elucidate risk patterns and pathophysiological mechanisms. Six opportunistic intestinal parasite genera were detected among ECS. The most notable species were Giardia duodenalis, Cyclospora cayetanensis, and Cryptosporidium spp., while seven were identified globally, with Strongyloides stercoralis and Cryptosporidium spp. predominating in LRCS. Remarkably, 70% of ECS patients exhibited polyparasitism, harbouring up to five different concurrent species, including both opportunistic and non-opportunistic parasites. Over half of the Egyptian patients were asymptomatic, while nearly one-third displayed extraintestinal manifestations, predominantly respiratory, which may reflect altered clinical presentation under corticosteroid-induced immune modulation. Prolonged corticosteroid therapy (≥1 month) was significantly associated with higher complication rates (p = 0.002) in ECS, and tissue invasion, organ dysfunction, hospitalization, and mortality in LRCS. The compiled LRCS mortality and hospitalization data (34 fatalities, 87 hospitalisations) reflect rare quantitative insight into global OIPI lethality under steroid exposure. This study provides the first integrated clinical and epidemiological synthesis linking corticosteroid exposure to complex parasitic dynamics across endemic and non-endemic settings. It advances the hypothesis that corticosteroids act less as mere infection triggers and more as amplifiers of pre-existing parasitic ecosystems, reshaping host–parasite interactions and facilitating subclinical dissemination. The findings underscore the importance of routine parasitic screening, risk stratification, and longitudinal monitoring before and during corticosteroid therapy, particularly in endemic regions, to ensure long-term patient care and prevent and manage OIPIs.