This study was conducted in the state of Yucatán in southern Mexico in three suburbs (San Lorenzo, Acim, Itzincab) of Merida (population ~1 million), the state’s capital (Fig 1 ). The three suburbs were small, densely populated ‘fraccionamientos’ (neighborhoods) connected to Merida by a single road and similar in housing size and design (e.g., one story, brick-and-mortar homes with typically two bedrooms, one living room, one TV room, a bathroom and a kitchen), characteristic of high-density low-income housing in the region. Merida is located in a subtropical environment with mean temperatures ranging from 29°C in December to 34°C in July. The rainy season occurs from May to October and overlaps with the peak dengue transmission season between July and November, although cases occur year-round [17 (link)]. Dengue virus is widely distributed throughout the Yucatan peninsula, and the vector control strategies used by local authorities at the time of this study included ultra-low volume (ULV) spraying with the organophosphate insecticides chlorpyrifos and malathion and indoor space spraying with pyrethroids (deltamethrin) and organophosphates (malathion) for adult Ae. aegypti control. Recent published reports from the region categorized the populations of Ae. aegypti as resistant to type I and II pyrethroids (including deltamethrin) and completely susceptible to carbamates (including bendiocarb) [18 (link)]. Mutations had previously been detected at both loci on the voltage-gated sodium channel gene, resulting in the presence of both 1016I and 1534C [18 (link), 19 (link)].
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