Hidden burden: submicroscopic Plasmodium spp. infections in indigenous populations of the Peruvian Amazon.

BACKGROUND: Malaria remains endemic in Peru, particularly in the Amazonas Region, with the highest burden reported in the Río Santiago District, Condorcanqui Province. As part of ongoing malaria elimination efforts, special attention must be given to submicroscopic infections, which may serve as silent reservoirs that sustain transmission. This study aimed to determine the prevalence of submicroscopic malaria infections and to identify the sociodemographic and clinical-epidemiological factors associated with these infections in the indigenous communities of Río Santiago. METHODS: A cross-sectional study was conducted in four native communities, with data collected during wet season through active case detection interventions. Blood samples were collected from participants for both microscopic diagnosis and molecular confirmation (qPCR) of Plasmodium spp. infections, alongside sociodemographic and clinical data. Data analysis included descriptive statistics and univariate and multivariate regression models to assess factors associated with submicroscopic malaria infections. RESULTS: A total of 926 individuals were enrolled in this study, of whom 157 (17.0%; 157/926) tested positive for Plasmodium spp. Plasmodium vivax was the most frequently detected species by both microscopy and qPCR. The prevalence of submicroscopic infections was 8.5% (79/926), with the community of Caterpiza exhibiting the highest prevalence (20.3%; 35/172). Among submicroscopic infections, 74.7% (59/79) were asymptomatic. Multivariate analysis showed that asymptomatic individuals had 2.32-fold higher prevalence of submicroscopic infection (aPR = 2.32, 95% CI 1.63-3.29). Conversely, the presence of household animals was associated with a 36% reduction in prevalence (aPR = 0.64, 95% CI 0.48-0.85). Additionally, living in Caterpiza was significantly associated with a higher prevalence, with individuals showing a 2.34-fold compared to those living in Alianza Progreso (aPR = 2.34, 95% CI 1.68-3.24). CONCLUSIONS: Submicroscopic malaria infections were highly prevalent in the Río Santiago District, influenced by individual, household and community-level factors. These findings underscore the need for improved diagnostic strategies beyond symptom-based approaches such as molecular diagnostic tools within malaria surveillance systems to better detect and control hidden malaria transmission.