Factors Associated with the Prevalence of Dengue–Leptospirosis Coinfection in Patients Hospitalized for Febrile Syndrome

Background: In tropical regions, dengue and leptospirosis coexist and share a nonspecific clinical onset that hinders timely diagnosis. Coinfection may worsen the clinical course and increase mortality. Objective: To estimate the prevalence of dengue, leptospirosis, and coinfection among patients with febrile syndrome in Madre de Dios (Peru) and to identify associated clinical factors. Methods: Observational, analytical, cross-sectional, retrospective study conducted at a primary-level health facility. Clinical and laboratory records of patients with febrile syndrome seen in 2024 were analyzed. Categorical variables were summarized as frequencies (%) and numeric variables as mean ± SD or median [IQR]. Comparisons used chi-square or Fisher’s exact test, Student’s t test, or the Mann–Whitney U test, as appropriate. Associations were estimated using Poisson regression models with robust variance, adjusted for sex, reporting prevalence ratios (PRs) and 95% CIs. Analyses were performed in R 4.0.2. Results: A total of 226 patients were included. Positivity was 19.0% for dengue (43/226), 66.8% for leptospirosis (151/226), and 5.8% for coinfection (13/226). In the bivariate analysis, dengue was associated with higher temperature (p < 0.001), lower mean arterial pressure (p = 0.007), mucosal bleeding/ecchymosis (p = 0.049), and lower fluid intake (p = 0.021); temperature was also higher in coinfection (p = 0.021). In Poisson models, dengue was associated with tachycardia (PR = 5.69; 95% CI: 1.95–13.07; p < 0.001), temperature (PR = 1.61 per °C; 1.23–2.12; p = 0.001), bilateral polyarthralgia (PR = 2.55; 1.14–5.04; p = 0.012), and mucosal bleeding/ecchymosis (PR = 3.31; 0.94–8.37; p = 0.027). Leptospirosis was associated with male sex (PR = 0.78 vs. female; 0.65–0.94; p = 0.010) and fever (PR = 2.38; 1.17–6.03; p = 0.035). Leptospira–dengue coinfection was related to higher temperature (PR = 1.75 per °C; 1.05–3.01; p = 0.036). Conclusions: Simple clinical signs such as fever/elevated temperature, tachycardia, bilateral polyarthralgia, and mucosal bleeding can help prioritize suspicion of dengue, leptospirosis, or coinfection; guide requests for dual testing (dengue–Leptospira), early hydration in dengue, and timely initiation of antibiotic therapy in leptospirosis. These findings support the development of integrated triage algorithms and strengthening access to molecular diagnostics in high-burden febrile syndrome settings.