In 2015, the first outbreak of Zika virus was reported in Latin America and the Caribbean (LAC), and was subsequently associated with a spike in congenital malformations (referred to as congenital Zika syndrome) and other neurological complications such as Guillain–Barre syndrome. By August 3, 2017, there were approximately 217,000 confirmed cases of Zika virus in the region [1]. While the outbreak has subsided, Zika is now considered endemic throughout LAC, in addition to parts of Africa and Asia [2]. Although Zika is unique among arboviruses because it can also be transmitted sexually, the virus is mainly transmitted by the Aedes aegypti mosquito, the same vector as other arboviruses, including dengue and chikungunya [3]. While several Zika programs in the LAC region direct their programmatic efforts to address both sexual transmission and vector control, the focus for this paper will be household vector control activities.
Ae. aegypti mosquitoes are historically a challenge for vector control programs; despite concerted elimination efforts since the 1950s, a resurgence of the arboviral diseases they transmit has been reported in recent years [4, 5]. This resurgence is in large part due to rapid, unmanaged urbanization in tropical cities, human migration, globalization, environmental changes, erratic water supplies leading to water shortages and insecurity, growing insecticide resistance, and ineffective or unsustainable vector control [6,7,8]. Eliminating Ae. aegypti breeding sites by targeting the immature aquatic stages (pupae and larvae) is considered to be one of the most effective household vector control interventions to control transmission of arboviruses such as Zika [7]. However, implementation is challenging, as the Ae. aegypti mosquito is highly anthropophilic, can reproduce in small amounts of water (e.g., in a bottle cap), and their eggs can survive being dry for more than a year [6, 9]. With unreliable piped (also known as reticulated) water supply, households in the region store water to fulfill basic needs related to cleaning, cooking, and drinking. This water often reaches the home via a piped water supply system managed by the local government. Although often unsafe for drinking, the piped water should not contain mosquito larvae, yet once stored in containers, the stagnant water may create potential mosquito breeding sites. If source reduction is to be effective, a multidisciplinary response is needed, addressing water access, urban planning, and behavior change strategies at the household and community levels.
In households, there are several behaviors being promoted as part of an integrated vector management strategy. Some require visits from vector control workers (for example, larvicide application), but many can be done by individuals at home [7]. As part of the United States Agency for International Development (USAID) Zika response in the region, social and behavior change programs promote three preventative vector control behaviors: eliminating standing water (e.g., throwing out tires where water accumulates), cleaning water storage containers at least weekly to eliminate eggs from the walls of the container, and covering containers with lids. Studies from other regions have found use of a lids to be effective [10,11,12]. Container lids are not an absolute barrier, but if tightly fitted, they are shown to be able to prevent gravid female mosquitoes from entering and laying eggs inside the container along the water line [12,13,14]. While lids can be effective, they require correct application by the user. However, most studies do not detail the characteristics of the lids, only reporting on presence or absence of any lid [15,16,17,18,19,20,21]. Additionally, most studies include use of a lid as one component of a multipronged approach, for example in combination with community mobilization efforts [22], school-based information and education campaigns, weekly clearing of stagnant water [23], and larvicide use [24].
Although many Ae. aegypti interventions including lids are not new, a recent review states that there is a paucity of reliable evidence regarding what vector control methods are effective for reducing abundance of Aedes larvae, particularly with few rigorous study designs such as the randomized trial [6]. Covering water containers with lids has long been promoted to prevent Ae. aegypti breeding sites; however, their effectiveness in rigorous research studies is not always clear-cut. For lids to be effective, they should not have holes, should hermetically seal the container, and they should not dip into the water or have water accumulated on them, creating a secondary breeding site on the lid. A study in Thailand found correct use of lids was effective in reducing the presence of larvae in jars used for storing water, defined as the lid fully covering the container [12]. However, the authors found that frequent use of the jars reduced the effectiveness of lids. While frequent emptying of containers can interrupt the mosquito life cycle, removing and replacing the lid too often reduced effectiveness [12]. A separate randomized trial in Mexico and Venezuela assessing the effectiveness of insecticide-treated water container covers found that these significantly reduce the number of larvae detected [16]. Field-based studies often report on the use of water storage container lids as one component of a larger intervention, making it difficult to isolate the effect of the lids. There is also limited description in published studies regarding the characteristics of lids that may make them more (or less) effective.
This is the first study conducted in the LAC context to provide detail on the use of different types of washbasins, containers, and lids and to explore the association between use of an effective lid and the presence of larvae. We explored household use of lids on washbasins and long-term water storage containers (mainly large plastic drums). Data collection involved a household survey and a direct observation checklist tool. Logistic regression modeling was used to estimate the relationships between lids and presence of mosquito larvae, adjusted for household demographic factors and other vector control activities.