For dengue fever, for example, every summer the health authorities conduct a search for areas with high numbers of the kinds of mosquitoes that carry that illness as a clue to which areas are most at risk.
譬如每到夏天，衛生單位就得四出搜尋白線斑蚊與埃及斑蚊，「病媒蚊」指數高的地方，就是可能爆發登革熱的高危險區，必須全面撲滅蚊蟲。