Sentinel surveillance of acute febrile illness in a Brazilian Amazon region: laboratory findings and epidemiological implications.

Abstract

The Amapa State, Brazil, in the Amazon region and bordering French Guiana, is a strategic sentinel location for infectious disease surveillance. Ecological pressures such as deforestation, artisanal gold mining, and high human mobility contribute to complex transmission dynamics of arboviruses, bacterial infections, and other pathogens. This study aims to characterize the etiologies of acute febrile illness (AFI) reported in Amapa State in 2018-2020, focusing on arbovirus circulation, bacterial contributions, and emerging pathogens. A retrospective analysis was carried out with 727 AFI cases. Laboratory diagnoses were established using molecular and serological assays, with systematic testing for different pathogens. Definitive diagnoses were obtained in 185 individuals (25.4%), yielding 209 positive results and including 23 cases of co-infection. Dengue virus was the predominant etiological agent (n=109, 52%), followed by leptospirosis (n=20, 9.5%), chikungunya virus (n=16, 7.6%), parvovirus B19 (n=16, 7.6%), measles (n=15, 7.1%), zika virus (n=10, 4.8%), mayaro virus (n=1,0.5%), and other bacterial infections (n=5, 2.4%). Isolated cases of hepatitis A and B, malaria, SARS-CoV-2, enterovirus, and acute Chagas disease were also identified. No hepatitis E virus or oropouche cases were detected. Dengue virus was the leading cause of AFI. Leptospirosis, chikungunya virus, and parvovirus B19 were other prevalent and often underrecognized contributors. The detection of additional viruses highlights Amapa State as a potential zone of "silent expansion" for emerging arboviruses. Co-detection of multiple pathogens underscores diagnostic complexity in regions with overlapping transmission. Strengthening surveillance, expanding laboratory capacity, and prioritizing differential diagnostics are essential to capture epidemiological dynamics and guide public health interventions.