The presence of water in both natural and artificial containers is important in a mosquito’s life cycle. The two most common species Aedes aegypti and Aedes albopictus are competent vectors of dengue, yellow fever, and chikungunya viruses [1]. These species live in close contact with humans [2] and exploit artificial and natural containers inside and near households for their immature life stages: these containers include water storage containers, discarded rainwater-retaining materials, tree holes, and plant axils [3].
In most studies examining the relationship between household water containers and the risk of mosquito-borne diseases, water containers were not classified according to their function (i.e., intentional and unintentional water storage containers) [4–8]. These studies emphasized that households use various water containers mainly to reserve water because of the uncertainty in tap water availability. Dhar-Chowdhury et al. [9] introduced the following five categories of water containers according to their functions: 1) household chores, 2) ornamental purposes, 3) amenities, 4) discarded containers, and 5) repairing and reconstruction purposes. However, having five categories seems unnecessary when specifically examining the relationship between the availability of water storage containers and the household’s water supply condition. The household chore category is the only category that is mostly related to water storage practice, while the rest of the categories can be merged into one, which is the unintentional water storage category. Thus, the present study classified the water storage containers into two: intentional and unintentional water storage containers. Intentional water storage containers are utilized for storing water for daily household use, whereas the unintentional water storage containers are not intended for storing water. Using these two categories facilitates in the formulation of a more targeted control strategy that is specific to the type of water storage containers at the household level.
Water storage containers in households have been extensively reported to play a vital role in the presence and increase of immature vector (larvae and pupae) prevalence. Stewart Ibarra et al. (2013) demonstrated that households that stored water containers such as cisterns or tanks had greater odds of containing A. aegypti pupae than those households that either did or did not store water but did not have a cistern or tank [10]. The same results were reported by Barera et al. (1993) in Venezuela [5]. From their surveillance, 71% (245/344) of the households had at least one container with A. aegypti immatures, and nearly half (788/2036) of the water containers were infested with the Aedes aegypti immatures. Moreover, Nguyen et al. [4] conducted a study in rural areas of southern Vietnam and found that as the number of water storage containers increases, the number of A. aegypti larvae also increases. Interestingly, these entomological studies only investigated the prevalence of larvae, not adult mosquitoes, in water storage containers. We considered such exclusion as a limitation because compared with immature mosquitoes, adult female Aedes mosquitoes transmit the virus to humans [11]. However, to our knowledge, no studies had investigated the relationship between the water storage containers and the abundance of adult Aedes mosquitoes.
The abundance of mosquito vectors in water storage containers are measured by various indices, with house index (HI) and container index (CI) as the most widely used; meanwhile adult mosquito index (AI), as the name implies, is the index used for adult mosquito abundance. HI refers to the proportion of households with larvae, CI is the proportion of water-holding containers with larvae, and AI is the proportion of adult mosquitoes in households. The AI is ideal use because it is highly accurate in predicting the occurrence of dengue transmission risk [12].
The prevalence of immature vectors (e.g., pupae) is also reportedly linked to water supply conditions such as the absence of piped water connection and unstable supply of tap water in households. A multicountry study, which included Myanmar, India, Indonesia, Philippines, Sri Lanka, and Thailand, investigated the association between water supply and Aedes pupal production; in Myanmar, irregular supply of tap water as well as the absence of piped water had the highest pupae per hectare index (PHI) among all those of countries involved [7]. Another multicountry study including Latin America, particularly in Ecuador, found a similar condition; this study revealed that not all households within the study cluster sites had access to piped water connection and that water supply was irregular and unavailable through the public network on a daily basis. Thus, households tend to acquire water from wells or rivers and store it in water storage containers [8]. In dry and wet seasons, 443 and 582 water storage containers contribute to the PHI of 35.0 and 150.2, respectively [8]. However, with regard to larval prevalence and adult mosquito abundance, their relationship with water supply conditions remains insufficiently investigated.
Makassar City is one of the largest and most urbanized cities in the eastern part of Indonesia. Covering an area of approximately 175.77 km2, this city is inhabited by roughly 1.5 million people, with 1.29% annual population growth in 2018 [13]. In the same year, the Regional Water Supply Company or the Perusahaan Daerah Air Minum (PDAM) of Makassar was only able to serve approximately 62.01% of the total population [14]. This water company operates five water treatment plants (WTP) that have a total design capacity of 2375 liters per second (L/s). However, the actual production is only 2354 L/s because of losses in the distribution system (e.g., leaks in old pipes) and seasonality of raw water quantities [15]. Furthermore, dengue epidemiology in Makassar increases. In 2015, 142 dengue cases were reported, with an incidence rate (IR) of 10.08 per 100,000 population and a case fatality rate (CFR) of 3.52% [16]. Unfortunately, these rates increased almost twice (248 cases) in 2016 (IR, 27.35 per 100,000 population; CFR, 0.5%) [17].
In this study, the prevalence of water storage containers was estimated in each household, categorizing them into two: 1) intentional water storage containers and 2) unintentional water storage containers. Then, we compared the prevalence of Aedes larvae between these two categories to identify the preferred breeding site of mosquitoes. We also examined the relationship of water storage container categories with water supply conditions (i.e., the availability of tap water connection, main source of clean household water, and the level of tap water supply stability) and with larval prevalence and adult Aedes mosquito abundance. We also assessed the relationship between larval prevalence and the indices HI, CI, and AI. On the basis of the literature, first, we hypothesized that water storage containers would be prevalent in the households, which would also have a high prevalence of larval mosquitoes. Second, we hypothesized that the availability of piped water connection, use of tap water, and a highly stable supply of tap water in a household would contribute to the reduction in the number of water storage containers, eventually decreasing larval prevalence and adult Aedes mosquito abundance. This study further determined the relationship between the three indices and found a positive correlation among them.