High seroprevalence and risk factors for Toxoplasma gondii infection in Iquitos: A city in the Peruvian Amazon

Background Toxoplasmosis, caused by the intracellular parasite Toxoplasma gondii , is a globally distributed infection with particularly high prevalence in tropical regions. Despite its high endemicity, population-based epidemiological data for the urban Amazon are scarce. This study aimed to determine the seroprevalence of T. gondii and identify sociodemographic and behavioral factors associated with T. gondii infection in the urban population of Iquitos, the largest city in the Peruvian Amazon. Methodology/principal findings A cross-sectional study was conducted between July 11 and August 10, 2024. Serum samples were collected from 382 adults across four urban districts of Iquitos and tested using an in-house ELISA (sensitivity 98%, specificity 100%) for T. gondii -specific IgG antibodies. All 358 IgG-seropositive participants were tested for IgM antibodies. Bivariate and multivariable Poisson regression analyses with robust variance were performed to identify factors associated with seropositivity. The overall IgG seroprevalence was 93.7% (358/382; 95% CI: 90.8–95.9%), and IgM seroprevalence was 1.7% (6/358; 95% CI: 0.62–3.6%) among IgG-positive individuals. In multivariable analysis, age above 60 years (adjusted prevalence ratio [aPR]: 1.10; 95% CI: 1.04–1.17; p = 0.002), and monthly family income in the 372–593 USD bracket (aPR: 1.07; 95% CI: 1.01–1.15; p = 0.035) were independently associated with IgG seropositivity. Additionally, peri-urban/rural residence (aPR: 1.04; 95% CI: 1.01–1.08; p = 0.025) and use of river or rainwater as a drinking water source (aPR: 1.08; 95% CI: 1.02–1.14; p = 0.010) were independently associated with seropositivity, whereas living in brick/cement housing was negatively associated with seropositivity compared with wooden housing (aPR: 0.95; 95% CI: 0.91–0.99; p = 0.037), suggesting waterborne transmission and structural poverty as key environmental drivers of infection in this setting. Conclusions/significance This study documents near-universal exposure to T. gondii in the urban population of Iquitos, underscoring toxoplasmosis as a major public health concern in the Peruvian Amazon. Age, income level, and peri-urban/rural residence were independent predictors of seropositivity. These findings support the prioritization of surveillance and prevention strategies targeting older adults and lower-income households in peri-urban areas, alongside environmental sanitation improvements.