Syndromic Surveillance as a Tool for Early Detection of Infectious Diseases in North-Western Karnataka, India: A Virus Research and Diagnostic Laboratory Experience

Abstract Rationale The Government of India has established a network of Virus Research and Diagnostic Laboratories (VRDLs) to strengthen disease surveillance and response to outbreaks. However, comprehensive laboratory-based evidence on the epidemiology of multiple pathogens remains limited. This study reports the co-circulation of infectious pathogens to understand the local epidemiological trends. Method ology: We conducted a retrospective cross-sectional analysis on 939 suspected patients presented with a varied spectrum of clinical signs using the syndromic approach in Belagavi, Karnataka (July 2024 - June 2025). We screened the samples for >25 pathogens, subjecting to 3,213 diagnostic tests of Enzyme-Linked Immunosorbent Assay (ELISA) and Polymerase Chain Reaction (PCR) targeting diagnostic marker genes. Results Out of 3,213 diagnostic tests performed, 399 were positive, yielding a total positivity rate of 12.4% (399/3213). Dengue (19%, 165/867 positivity) was the most frequently detected pathogen, followed by leptospirosis (12.9%, 86/866 positivity) and scrub typhus (5.8%, 31/536). Adults aged 21–40 years were the most affected (51.3%). Other predominant co-circulating infections are leptospirosis and scrub typhus. Notably, 18 cases of dengue–chikungunya coinfection were identified exclusively among patients presenting with fever and rash syndromic approach. The highest burden of infection was observed in the 21–40-year age group. Conclusions The integration of viral (dengue, chikungunya, hepatitis viruses, influenza, etc.), rickettsial (scrub typhus), and bacterial (leptospirosis) diagnostics within a single surveillance framework is more comprehensive. Demonstrates the limitations of single-pathogen testing approaches and provides evidence for expanding "Essential Panel" recommendations for Karnataka to enable timely and accurate diagnosis and improve public health response.