High prevalence and territorial heterogeneity of intestinal parasite detection in Ecuador: A large registry-based cross-sectional study using routine stool examinations.

BACKGROUND: Intestinal parasitic infections (IPIs) remain a significant public health challenge in Ecuador, yet most available evidence derives from small-scale, pediatric, or localized studies. This study aimed to describe the prevalence and coproparasitological profile of IPIs using routine stool examinations from a reference private laboratory with coverage across the country's three natural regions.

METHODS: We conducted an observational, analytical cross-sectional study based on secondary analysis of laboratory information system records. All routine stool ova-and-parasite examinations performed in Quito (Highlands), Guayaquil (Coast), and El Coca (Amazon/Oriente) between January 1, 2020, and December 31, 2024, were eligible. For prevalence and association analyzes, only the most recent examination per individual was included (patient census, n = 101,967). Associations were evaluated using Pearson's chi-square tests; age distributions by parasite type were compared with Kruskal-Wallis tests; and multiple correspondence analysis explored joint patterns by parasite profile, sex, and city.

RESULTS: We analyzed 101,967 unique patients, corresponding to 127,601 stool examinations. Adults aged 20-64 years represented 74.1% of the sample. The overall detection rate of at least one intestinal parasite in the most recent examination was 41.6% (42,437/101,967), slightly higher in men than in women (43.3% vs. 39.8%, p < 0.001). Blastocystis spp., an intestinal parasite taxonomically classified as a stramenopile, was the most frequently detected organism nationally, occurring in 28.3% of all patients and 68.0% of patients with a positive examination. It was followed by commensal protozoa and the Entamoeba histolytica/E. dispar complex. Pathogenic or potentially pathogenic protozoa were detected in 5.2% of all patients and 12.4% of positive patients, whereas helminths were uncommon, occurring in 0.02% of all patients and 0.06% of positive patients. Giardia lamblia detection clustered significantly in younger age groups (p < 0.001). Intestinal parasite detection was associated with age group, reproductive-age status among women, and decreased bacterial flora (all p < 0.001). Multiple correspondence analysis revealed distinct territorial patterns, suggesting heterogeneous fecal-oral exposure profiles across Ecuador's Coast, Highlands, and Amazon regions.

CONCLUSIONS: Routine stool microscopy showed a high frequency of intestinal parasite detection in Ecuador, including among adults, with heterogeneous patterns according to age and territory. Blastocystis spp., an intestinal parasite classified as a stramenopile rather than a protozoan, was the most frequently detected organism. However, a substantial proportion of the detected organisms were commensal or of uncertain pathogenic significance, and clinical symptoms were not systematically available. These findings should therefore be interpreted as routine laboratory detection and exposure patterns rather than as confirmed symptomatic parasitic disease. Strengthened water, sanitation, and hygiene interventions, improved surveillance, and complementary molecular or antigen-based diagnostic methods are needed to better distinguish colonization from clinically relevant infection.