The risk was already there: infectious disease importation at the 2026 FIFA World Cup

Objectives: The 2026 FIFA World Cup will draw an estimated 3.5 million visitors from 48 nations to 11 US host cities. We estimated city-level importation risk for five infectious diseases with propagated uncertainty. Methods: Three nested Poisson models were fitted: a pre-tournament baseline (M1), a World Cup-adjusted model (M2), and a schedule-driven model (M3) allocating fans by match venue. Parameter uncertainty was propagated via 5,000 Monte Carlo draws. A diaspora extension using US Census data estimated co-national network entry probabilities at 11 host cities and 15 non-venue cities. Results: Under M3, importation probability exceeded 0.99 for dengue at Miami, New York, and Houston (median $\Lambda = 45.0$, 95\% CI 16.0--92.3) and for malaria at Atlanta and New York. Baseline travel accounted for 86--93\% of importations; the World Cup added only 7--14\% above this pre-existing risk. Dengue diaspora-network entry probability was highest at Dallas (0.43), Houston (0.39), and Los Angeles (0.35); non-host cities exceeded most venue hubs. Conclusions: Dengue is the dominant importation risk (Miami, New York, and Houston); malaria dominates at Atlanta and New York. City-level surveillance with targeted diaspora community outreach in host and non-host cities is warranted. The schedule-driven Poisson framework is directly transferable to future mega-events.