Clinical features of yellow fever in cases from Bolivia, Ecuador, Colombia, and Peru (2023-2025): A descriptive retrospective study.

Background: Yellow fever (YF) persists as a major arboviral threat in South America, despite the availability of an effective vaccine. While Brazil has produced extensive clinical descriptions, data from Bolivia, Ecuador, Colombia, and Peru remain limited. Methods: We conducted a descriptive retrospective multicenter analysis of laboratory-confirmed YF cases reported between January 2023 and August 2025 in four Andean countries. Demographic, epidemiological, clinical, and laboratory data were extracted from hospital and surveillance records. Results: Twenty-one confirmed cases were identified: Bolivia (n = 8), Ecuador (n = 5), Colombia (n = 4), and Peru (n = 4). The median age was 25 years (IQR: 16-43), with a predominance of males (81 %). Vaccination history was largely undocumented; 86 % had unknown or absent records. The median delay from symptom onset to hospitalization was 5 days. Outcomes were severe, with a case fatality rate of 57 % (12/21), and the median time from symptom onset to death was 8 days. Early manifestations included fever (71 %), arthralgia (19 %), headache (19 %), and myalgia (19 %). During the toxic phase (severe disease), hemorrhage (86 %), jaundice (62 %), circulatory collapse (57 %), and hepatic dysfunction (52 %) predominated. Complications included intracranial hemorrhage, multiorgan dysfunction, sepsis, and renal failure. Laboratory findings revealed marked hepatic injury (AST median, 3257 U/L; ALT median, 1570 U/L), hyperbilirubinemia, metabolic acidosis, elevated lactate levels, hypoglycemia, and coagulopathy. RT-PCR for YFV was positive in 95 % of tested cases. Conclusions: This study provides one of the first systematic clinical characterizations of YF cases from Bolivia, Ecuador, Colombia, and Peru. The high fatality rate, despite the young age of patients, underscores the vulnerability of populations in resource-limited, peri-Amazonian settings. Severe hepatic dysfunction, hemorrhage, and systemic collapse were consistent hallmarks of the disease. These findings highlight the urgent need to strengthen vaccination coverage, enhance clinical recognition, and expand access to critical care in outbreak-prone areas of South America.