This is the first cross-sectional study assessing the ownership and utilization of bed nets among the border population in Tha Song Yang District of western Thailand. The results of this study revealed that the ownership of bed nets is very high (98.49%), while 246 (74.32%) had at least one treated nets. Bed nets are highly available in these localities, a result of efforts by the Department of disease control and other partners (such as non-governmental organizations) that have distributed free LLINs from the Global Fund . The results are consistent with the finding of the Mobile and Migrant Population Survey in Thailand , which found that households with any nets were 94% in 2017, whereas households with at least one ITN were 39%. Also, Kitidamrongsuk et al , reported that almost all households (92.9%) in Prachuab Khiri Khan, Thailand had at least one mosquito net, whereas 41.1% of households owned at least one ITN/LLIN. Similar studies in Myanmar showed high coverage of bed nets among households of Kachin Special Region II population , and 50–65% coverage of ITN/LLIN among households of migrant population [15, 16]. The WHO advocates for universal coverage of ITN/LLINs with one net for every 2 persons . In spite of the high-level ownership of and access to bed nets in this study because of the LLIN distribution campaign, only 30.82% of all households had sufficient numbers of ITN/LLIN for one ITN/ LLINs per two persons. This insufficiency might be due to the operational challenges of the LLIN distribution system, as some studies identified operational barriers to continuous LLIN distribution [18, 19]. This study suggests that the insufficiency of ITN/LLIN is also a concern and can be used as an indicator for the LLIN distribution program. Plucinski et al. reported that the access indicators of LLINs were high in Mozambique when the bed net distribution campaigns used a novel distribution model and used LLINs designated for each sleeping space . Thus, the LLIN distribution systems in Thailand should be evaluated in the future.
Globally, malaria-related morbidity and mortality are highest in children and pregnant women . Most children in this study used bed net in the previous night (95.3%). Overall bed net usage among adults was lower than among children. This was mainly due to the high focus on vulnerable age groups. However, only 59.58% of the children used ITNs/LLINs. This result is consistent with the previous findings in Myanmar and some countries in Africa [6, 15, 16, 22–26], which showed that the utilization of ITN remained moderate or low among children. However, it differs from the previous reports of high use rate of ITNs/LLINs among children [14, 27, 28]. Pregnant women, particularly primigravidas with malaria, have a high risk of severe malaria and low birth weights [29, 30]. This study showed a high rate of ITN/LLIN use among pregnant women (90.00%). However, in many parts of the world, ITN usage remained moderate or low among pregnant women [6, 16, 22, 23, 28, 31].
One of the major factors in not using bed nets in our data was the use of different sleeping sites. Work and evening activities in the forest impact where community members choose to sleep on any particular evening. Together with the previous findings in Prachuab Khiri Khan province  and Southern Thailand , sleeping elsewhere especially at temporary shelters in the plantation is another non-use reason.
Another major factor in bed net use was net manufacturing materials and size are other factors affecting net utilization among households with more family members . Many other studies reported under usage of nets due to the lack of sufficient nets to cover all household members [7, 15, 26, 27, 33–35]. Household socio-economic status has likewise been shown to influence bed net access and is the strongest determinant of net use [28, 36–43]. Our study showed that wealthier families were significantly more likely to use bed nets every day than the poorer families, likely because of the ability to purchase bed nets for use outside the home.
Consistent with previous studies [44–47],the perceived role of bed nets as a means to protect against mosquitoes and malaria was a significant predictor of seasonal bed net use. In our research, participants reported higher bed net usage during the rainy season. Aside from malaria prevention, the main reason for sleeping under nets was because they provided comfortable sleep and protected against biting insects (including mosquitoes).
Other reasons for the not using bed nets were in line with other research [7, 16, 48–57] suggesting that discomfort from heat and low mosquito density are common reasons for non-adherence. Complacence, the inadequate number of of bed net, rough materials of bed net, not having a routine of bed net use, use of alternative mosquito control methods, and too small size of free bed nets were the other most commonly cited reasons for not using a net at home. Some studies have shown that bed nets decrease airflow, making it feel hot and stifling under a net [48, 58, 59]. In seasons of low and/or variable mosquito nuisance, education will need to emphasize that the risk of malaria is not necessarily diminished when mosquito numbers are perceived to be low.
The reasons for not using bed net in the forest were also consistent with some past studies in the greater Mekong subregion [60–62]. Some forest-goers described the inconvenience of carrying bed nets, while others found inadequacy of nets for use when visiting the forest. This study suggests that the campaign of LLIHN distribution appeared not effective for malaria prevention among forest goers. The advantages of these nets might be not adequately promoted. Other strategies to address outdoor transmission may need to be considered among this population [63–65].
Previously reported limited effectiveness of bed nets in Southeast Asia may have resulted from the vector feeding behavior and human activities that in some circumstances increase human-vector contacts [66, 67]. Some main malaria vectors such as Anopheles minimus, Anopheles maculatus and Anopheles dirus feed outdoors at dusk between 6 and 7 p.m. when people are not in bed [66, 68]. Also, forest goers exhibit behaviors (hunting or fishing) that reduce the protection of ITNs at peak biting times [69, 70]. Despite high coverage and utilization of bed nets in this study, the bed net use behavior of people may also affect the effectiveness of bed nets. Some did not use bed net every day, especially in summers and when they stayed overnight in the forest or the field. Some did not deploy bed nets properly, used damaged/torn nets, and used untreated nets. Nevertheless, given the broader impacts of ITNs for preventing all vector-borne diseases such as malaria [71, 72], Japanese encephalitis , and leishmaniasis , proper net distribution and encouraged use still need to be strengthened, especially for the high-risk populations such as the forest goers.
Outdoor transmission remains the main challenge for malaria elimination program in Thailand. This transmission is influenced by human behavior, including efforts at preventing exposure to mosquito vectors. At least one study (from Tanzania) has shown that relatively modest coverage (53.13% ITNs use) in the community can lead to community-wide protection against malaria . However high risk groups such as Karen ethnic groups living along the border and forest goers may not receive the same benefits of the protection. In our study, low use of bed nets when overnighting in the forest was related to perceptions of inconvenience of carrying and using bed nets, insufficient numbers of bed nets to use outside the home, and low perception of bed net necessity. Therefore, interventions among these high risk groups should pay attention to factors beyond bed net coverage, and use and look for long-lasting new tools or approaches for preventing exposure to mosquito vectors to decrease outdoor malaria transmission.
Study limitations included 63.14% of heads of households were female. However, female heads of households should be in better position to respond about ownership and use of bed nets of every household member. This study was conducted in Thasongyang district; therefore, the results could represent population living along Thai-Myanmar border and Karen ethnic groups, but not represent Karen groups from other areas in which lifestyle, culture, or health operation were different. Due to the limitation of budget and time, this study was conducted in one season (rainy season with more abundant of mosquitoes) which may result in high rate of bed net use in the previous night. Nonetheless, adding question of everyday use of bed net, should reduce the bias from season differences.