This study was approved by the institutional ethics committee of Saint Camille Hospital of Ouagadougou (HOSCO) N˚ 2022-21/12-09 of 21 December 2022, ensuring ethical compliance in the use of patient data.

A descriptive analytical study was conducted to assess the seroprevalence and progression of dengue virus infection among patients at HOSCO, from January to December 2023. Ouagadougou has a tropical savanna climate characterized by a long dry season (October to May) and a rainy season (June to September), with average annual temperatures around 28˚C and marked variations in humidity. These climatic conditions, particularly the rainy season, favor the proliferation of Aedes mosquitoes, the main vectors of dengue, and thus contribute to seasonal peaks in infection.

The study included 6474 patients of various ages and sexes who attended general medical consultations and were referred to the hospital’s laboratory for dengue serological testing during the study period. Patients were eligible if they presented with clinical suspicion of dengue fever and were referred by a physician for serological confirmation. Individuals whose medical records were incomplete were excluded from the study. The individuals included were considered representative of the broader population of Ouagadougou, as HOSCO receives patients from all districts of the city as well as from surrounding areas.

Venous blood samples were collected in dry tubes or EDTA tubes. After centrifuging at 4000 rpm for 5 minutes, serum or plasma was extracted and used for dengue testing. Serological tests were performed immediately after sample collection to ensure rapid availability of results.

Dengue virus infection was diagnosed using the SD Bioline Dengue Duo Rapid Detection Kit (Standard Diagnostics Inc., Korea), following the manufacturer’s protocol. This test detects nonstructural protein 1 (NS1) antigen and anti-dengue virus IgG/IgM antibodies in serum, plasma, or whole blood.

Data were recorded in Microsoft Excel 2019 and analyzed using Statistical Package for Social Sciences (SPSS) version 26.0 software (SPSS Inc., Chicago, IL, USA). Multivariate logistic regression was employed to examine the effects of age and gender on dengue infection. Statistical differences were considered significant at p < 0.05.3.

Define The study population consisted of 57.3% females (3710/6474) and 42.7% males (2764/6474). Patient ages ranged from 0 to 98 years, with a mean age of 27.14 years and a median of 26.0 ± 18.12 years. The most represented age group was 25 - 40 years, accounting for 31.4% (2034/6474) of the study population ( Table 1 ).

In the study population, 28.2% (1826/6474) of the subjects tested positive for at least one of the three serological markers of dengue infection. The prevalence of

NS1: Non-structural Protein 1, Immunoglobulin M (IgM), Immunoglobulin G (IgG).

dengue NS1 Ag was 16.7% (1080/6474), with a frequency of 15.0% (556/3710) in females compared to 19.0% (524/2764) in males (p < 0.001, OR = 0.754, 95% CI = [0.661 - 0.859]). The seroprevalence of IgM and IgG was 4.1% (264/6474) and 11.7% (758/6474) in the study population, respectively ( Table 1 ). Multinomial logistic regression also revealed a sex difference in IgM positivity, with a prevalence of 5.0% in males compared to 3.4% in females (p = 0.02, OR = 0.680, 95% CI = [0.531 - 0.870]).

The age group 16 - 25 years showed the highest positivity rates for NS1 Ag (22.1%, 321/1450) and IgM (5.7%, 83/1450) compared to the <5-year age group (p < 0.001, OR = 2.124, 95% CI = [1.637 - 2.756] and p = 0.02, OR = 2.311, 95% CI = [1.377 - 3.878], respectively). The age group 41 - 60 years had the highest positivity rate for IgG (17.0%, 139/819) ( Table 2 ). Individuals double positive for NS1 Ag/IgM and NS1 Ag/IgG represented 0.9% (56/6474) and 1.4% (92/6474) of the study population, respectively, while IgM⁺/IgG⁺ accounted for 1.1% (74/6474) ( Table 3 ). Triple-positive patients accounted for 0.4% (27/6474) of the study population, with males being twice as numerous as females among this group ( Figure 1 ).

NS1: Non-structural Protein 1, Immunoglobulin M (IgM), Immunoglobulin G (IgG).

NS1: Non-structural Protein 1, Immunoglobulin M (IgM), Immunoglobulin G (IgG).

No positive cases for dengue infection serological markers were recorded among the 241 individuals tested from January to March, representing 2.5% of the study population. In April, only 0.7% (2/270) of the cases tested positive for NS1Ag. The number of suspected cases tested in October accounted for 35.4% (2290/6474) of the study population, with a positivity rate of 24.8% (567/2290) for NS1 Ag. Overall, 78.4% of the study population was tested for dengue virus infection between September and November, with the peak of infections observed in October ( Figure 2 )

Females were predominant in our study population, consistent with previous studies conducted in the same setting [15] [17] - [20] . A key observation from the data is the higher prevalence of dengue infection markers among males compared to females. Specifically, males exhibited higher positivity rates for NS1 antigen and IgM antibodies compared to females. Multinomial logistic regression analysis confirmed that females had significantly lower odds of being NS1 Ag⁺ and IgM⁺ than males. A similar trend was observed in previous studies, where men were significantly more likely to be infected with dengue virus (NS1 Ag⁺) than women [17] - [19] . These gender disparities may be attributed to behavioral and occupational factors. Males might be more engaged in outdoor activities or occupations that increase exposure to mosquito vectors [21] . Similar patterns have been documented in other regions where cultural and social roles lead to differing exposure risks between genders [22] . However, it is important to acknowledge that other potential confounding factors such as socioeconomic status, access to healthcare, and pre-existing health conditions were not fully assessed in this study. Including such variables in future analyses would help to better isolate the independent effect of gender and other demographic characteristics on dengue infection risk. Understanding these differences is crucial for tailoring public health interventions that address specific risk factors associated with male populations.

The age group of 16 - 25 years demonstrated the highest positivity rates for both NS1 antigen and IgM antibodies. Compared to the reference group (<5 years), individuals in this age bracket had significantly higher odds of recent infection (NS1 Ag⁺/IgM⁺). Previous studies in Burkina Faso have found a higher prevalence of DENV infection among individuals aged 20 - 29 years [19] and 15 - 30 years [17] compared to children under five years. This heightened risk could be due to increased mobility, social interactions, and occupational exposures that are common in late adolescence and early adulthood. Conversely, the highest IgG positivity was observed in the 41 - 60 years age group (17.0%), indicating a greater accumulation of past exposure and potential immunity in older individuals. This pattern suggests that long-term exposure over the lifespan contributes to seroconversion and the development of protective antibodies [23] .

The temporal distribution of dengue cases highlights a pronounced seasonal trend. No positive cases were detected from January to March, and only minimal positivity was observed in April. A sharp increase in both testing and positivity rates occurred between September and November, with the peak in October. Specifically, 35.4% of the study population was tested in October, with a positivity rate of 24.8% for NS1 antigen. Previous studies reported that the peak of DENV infection in Burkina Faso generally occurred between October and November [17] - [19] . This seasonality aligns with environmental conditions favorable for mosquito breeding, such as increased rainfall and humidity during certain months [7] - [9] . The clustering of cases during this period underscores the need for seasonal preparedness in dengue surveillance and control efforts [10] . Public health strategies should intensify vector control measures and community awareness campaigns ahead of peak transmission seasons.

The study also examined the distribution of serological markers and their combinations. Individuals positive for both NS1 antigen and IgM antibodies represented 0.9% of the population, indicating acute infection with active viral replication and an immune response. Those positive for NS1 antigen and IgG antibodies (1.4%) suggest a recent infection in individuals with prior exposure. Triple-positive individuals (0.4%) were more prevalent among males, further emphasizing the gender disparity in infection rates. Previous studies have shown that men face a higher risk of death from severe dengue compared to women [24] [25] . Triple positivity was found to be predictive of severe thrombocytopenia due to dengue infection and was associated with a higher risk of mortality [12] .

While the study provides valuable insights, several limitations should be acknowledged. First, selection bias may be present, as the data were derived from individuals who sought testing, which may not represent the general population. Those tested might have had symptoms or concerns prompting testing, potentially leading to overestimation of prevalence rates. Second, the cross-sectional design of the study limits the ability to infer causality or temporal changes at the individual level. Longitudinal studies would be necessary to track infection progression and immunity development. Third, serological tests can cross-react with other flaviviruses, potentially affecting specificity. Moreover, NS1 antigen levels decline after the early phase of infection, which could result in underestimation of acute cases if testing is delayed. Finally, although the study reports the seroprevalence of different markers, data on clinical outcomes (e.g., hospitalization rates, severe dengue cases, or mortality) were not collected. Including such information in future studies would enhance the clinical relevance of the findings and provide a more comprehensive picture of the dengue burden.

This study nevertheless reveals a substantial burden of dengue virus infection within the population, with distinct gender- and age-related patterns. The higher seroprevalence among males and young adults points to specific groups at increased risk, necessitating targeted public health interventions. The seasonal peak in October emphasizes the influence of environmental factors on transmission dynamics and the critical timing for preventive measures. Future research should aim to include broader population samples, integrate clinical outcome data, and employ longitudinal designs to enhance understanding of dengue epidemiology. Incorporating climatic data and vector surveillance could further improve predictive models and guide effective control strategies. Collaborative efforts between health authorities, communities, and researchers are essential to reduce the impact of dengue and protect vulnerable populations.