Dual Viral Threats of Influenza and Emerging Chikungunya Fever in a Temperate City: Paediatric Perspectives.

Hong Kong's paediatric population is currently facing a dual viral challenge: a seasonal surge in influenza and the emergence of locally acquired chikungunya fever. As a temperate city during the winter surge of influenza, Hong Kong has limited experience with this unfamiliar mosquito- vector viral infection. Unlike other tropical cities without a winter influenza surge, such as Singapore, Malaysia and Thailand, our unique experience serves to guide local physicians and physicians in other temperate cities about the two viral infections. Hong Kong Centre for Health Protection (CHP) reported 16 severe pediatric influenza cases from early September 2025 through the end of October 2025, including one fatal case involving influenza B. Most cases were due to influenza A and occurred in previously healthy children aged 11 months to 17 years. Complications of influenza included encephalopathy, pneumonia, shock, sepsis, and myocarditis. Simultaneously, media reports have highlighted the detection of Hong Kong's first indigenous chikungunya case, raising concerns about vector-borne transmission. The co-circulation of these two febrile viral illnesses presents diagnostic and public health challenges for a temperate city that does not have much experience with chikungunya disease. Differentiating between influenza and chikungunya in a febrile patient requires a comprehensive approach that considers epidemiology, clinical features, and laboratory findings of these two febrile diseases. While both can cause a sudden febrile illness with systemic symptoms, the dominance of severe, symmetric, and potentially chronic polyarthralgia, along with a characteristic rash, distinguishes chikungunya, particularly in the context of recent travel to an endemic area, from influenza. In contrast, influenza is characterized by a prominent respiratory component. By following a structured diagnostic approach and utilizing targeted laboratory testing, physicians can accurately distinguish these illnesses, ensure appropriate patient management, and mitigate public health risks.