Seasonal variation and co-infection of dengue and typhoid cases in a tertiary care hospital: A cross-sectional analytical study

Background: In tropical areas of Pakistan, dengue and typhoid fever are the most common causes of acute undifferentiated febrile illness. Their similar clinical characteristics make diagnosis and treatment much more difficult. The aim of this study is to determine the seasonal distribution and quantity of co-infection between laboratory-confirmed cases of typhoid and dengue among hospitalized patients in tertiary care hospitals. Material and Methods: This cross-sectional analytical study was carried out at Quaid-e-Azam Medical College/ Bahawal Victoria Hospital Bahawalpur between January 2023 and December 2024. A total of 280 febrile patients with laboratory testing for both disorders and a fever (≥38°C for ≤10 days) were included. Typhoid was confirmed by blood culture for Salmonella typhi/ paratyphi, while dengue was confirmed by NS1 antigen detection. SPSS version 23.0 was used to evaluate data on demographics, clinical characteristics, and admission dates (classified into seasonal periods). Results: 112 (40.0%) of the 280 patients had dengue, 94 (33.6%) had typhoid, and 9 (3.2%) had two infections. Typhoid surged after the monsoon (October-November 61.7% of cases), but dengue peaked during the monsoon (July-September 78.6%). In September and October, seven out of nine dual instances took place. The only significant predictor of dual infection was admission after the monsoon (adjusted OR = 5.2, 95% CI: 1.4-19.3; p=0.014). Conclusion: There is a significant seasonal co-infection of dengue and typhoid during the post-monsoon transition, making integrated diagnostic and public health efforts necessary during this high-risk time. Keywords: Dengue; Febrile illness, Salmonella typhi, Seasonal variation, Typhoid fever