P-1598. Unseen but Present: Asymptomatic COVID-19 Cases and Air Travel to Hong Kong

Abstract Background The global spread of infectious diseases was significantly influenced by the dynamics of human movement patterns, particularly for highly transmissible infections such as the SARS-CoV-2 virus, which causes COVID-19. Asymptomatic COVID-19 cases did not exhibit symptoms prior to diagnosis, making them a potential challenge for containment. Understanding air travel patterns among asymptomatic individuals was crucial for controlling the spread of the virus, however, their contribution has been understudied. Methods Through a retrospective cross-sectional study, we analyzed 11,775 COVID-19 cases in Hong Kong. Log-binomial regression models were used to estimate the association between asymptomatic status and inbound air travel behavior 14 days prior to COVID-19 diagnosis. The median flight duration between asymptomatic and symptomatic cases was compared using the Wilcoxon rank-sum test. Results Approximately two-thirds of the COVID-19 cases with inbound air travel history 14 days prior to diagnosis were asymptomatic. We found a significant association between COVID-19 asymptomatic status and inbound air travel behavior, which was modified by cases’ occupation categories (p< 0.0001). The prevalence of inbound air travel was significantly higher among asymptomatic cases in airport or flight crew compared to symptomatic crew members (adjusted prevalence risk ratio: 10, 95% CI: 4-20), while the prevalence of inbound air travel in asymptomatic cases outside the airport or flight crew group was 1.14 times higher than symptomatic cases (95% CI: 1.12-1.16). The median flight duration of asymptomatic cases was 4.6 person-hours shorter compared to symptomatic counterparts (p< 0.01). Conclusion Asymptomatic COVID-19 cases indicated significantly higher prevalence of air travel within 14 days before diagnosis, suggesting potential under-detection during early travel restrictions. Asymptomatic airport and flight crew showed markedly higher travel prevalence than symptomatic counterparts, pointing to potential workplace transmission risks. These findings reveal limitations of symptom-based screening and highlight the need for proactive, symptom-independent public health strategies in future airborne disease outbreaks. Disclosures All Authors: No reported disclosures