Risk indicators and composite index for imported malaria re-establishment in Fuzhou, China: a 10-year study integrating case, vector, and meteorological surveillance data

BACKGROUND: Following China's malaria-free certification in 2021, imported malaria infections and the continued presence of Anopheles mosquitoes pose challenges for preventing local transmission in post-elimination settings. We integrated case, vector, and meteorological surveillance data to describe potential conditions for malaria re-establishment in Fuzhou, China. METHODS: We analyzed imported malaria cases reported during 2016-2025, vector surveillance records, and corresponding meteorological data. Five binary indicators-imported case presence, diagnostic delay, Anopheles presence, high Anopheles density, and favorable meteorological conditions-were combined into an exploratory monthly index. Risk scores were tabulated for the 60 months in the May-October surveillance seasons using the available routine surveillance information. RESULTS: A total of 663 imported malaria cases were reported, of which 611 (92.2%) originated from Africa. In the 37 months with matched vector and meteorological records, concurrent precipitation was positively associated with Anopheles density (Spearman's ρ = 0.360, P = 0.031), whereas mean temperature and dew point temperature 2 months earlier were negatively associated with density (ρ = - 0.504, P = 0.002; and ρ = - 0.578, P < 0.001, respectively). Of the 60 seasonal months, 28 (46.7%) were assigned low-risk scores, 27 (45.0%) moderate-risk scores, and 5 (8.3%) high-risk scores. All five high-risk months occurred in May or June. CONCLUSIONS: The exploratory index identified seasonal variation in the concurrence of routinely monitored indicators, with high-risk scores observed in May and June. Year-round case surveillance and timely diagnosis remain important, alongside vector monitoring during the surveillance season. Uneven monitoring coverage and the lack of validation against local transmission events limit interpretation of the resulting risk categories.