Population density and rainfall increase the incidence of Dengue Haemorrhagic Fever in West Java, Indonesia: a secondary data analysis from 2017 to 2021

Dengue Haemorrhagic Fever (DHF) is one of the seasonal/latent infectious diseases that potentially to become an epidemic if it is not anticipated properly. DHF cases in West Java, show fluctuating numbers and this province is one of the provinces in Indonesia with the most dengue cases each year. This study aimed to analyse the relationship between rainfall, temperature and population density with the incidence of DHF in West Java, Indonesia. This research was an analytical study using secondary data from 2017 to 2021. Data on population density and rainfall were obtained from the BPS Statistics of West Java Province, while DHF case data were obtained from the West Java Provincial Health Office. The data were analysed using ordinal regression. Results of this study found that the risk of increasing DHF cases in densely populated areas was 8.75 times higher than in less densely populated areas. This study also showed that the risk of increasing DHF cases in areas with high rainfall was 21.43 times higher compared to areas with low rainfall. Therefore, it can be concluded that the denser of the population and the higher of the rainfall, the greater risk of increasing DHF cases in the region.


Introduction
Dengue Haemorrhagic Fever (DHF) is a type of arbovirus disease that is transmitted by two types of mosquito vectors namely Aedes aegypti and Aedes Albopictus.[1] The disease is a health problem in the world, especially in tropical countries.This disease has spread and become endemic in more than 100 countries in Africa, the Americas, the Eastern Mediterranean, Southeast Asia and the Western Pacific.[2] World Health Organization (WHO) data shows that tropical countries are at risk of dengue virus infection with 96 million cases coming from 128 tropical countries.[3] This data showed that tropical countries as the largest contributor to dengue cases.When the disease spreads to new areas it causes an increase in cases and also explosive outbreaks.[3] Asia Pacific bears 75% of the dengue burden in the world between 2004 and 2010, while Indonesia is reported as the 2nd country with the largest dengue cases among 30 endemic countries/regions [4] The year 2016 was marked by a major outbreak of dengue fever worldwide.The Region of the Americas reported over 2.38 million cases in 2016, of which Brazil alone accounted for slightly less than 1.5 million cases, roughly 3 times higher than in 2014.1032 deaths from dengue were also reported in the region.The Western Pacific Region reported more than 375,000 suspected cases of dengue fever in 2016, of which the Philippines reported 176,411 and Malaysia 100,028 cases, representing a similar burden to the previous year for both countries.Solomon Islands declared an outbreak with over 7000 suspected people.In the African Region, Burkina Faso reported a localized dengue outbreak with a possible 1,061 cases.[3] The largest number of dengue cases ever reported globally was in 2019.All regions were affected, and dengue transmission was recorded in Afghanistan for the first time.The American Region reported 3.1 million cases, with more than 25.000 classified as severe.A high number of cases were reported in Bangladesh (101.000),Malaysia (131.000)Philippines (420.000),Vietnam (320.000) in Asia.[2] An estimated 500.000 people with severe dengue require hospitalization each year, and about 2.5% of those affected die.[3] The ease of transportation allow travellers to visit almost all locations in the world, including dengue endemic areas.This triggers a significant increase in dengue disease.[5] DHF cases in Indonesia were first reported in Jakarta and Surabaya in 1968.Subsequently, DHF cases spread to many areas and DHF cases was reported in 34 provinces and 514 districts/cities throughout Indonesia.[6] The incidence of DHF in Indonesia has increased 700 times over 45 years since 1968 with an annual burden of more than 750,000 cases.[7][8] West Java Province is the province with the most populous population in Indonesia.Dengue Hemorrhagic Fever in West Java Province since the 2000s it has increased dramatically from 13/100,000 in 2000 to 79/100,000 in 2016.[9] All regencies and cities in the province are at high risk for dengue transmission.Although the number of DHF sufferers in 2021 (23,959 cases) is slightly lower than in 2020 (24,471 cases) and the risk of DHF incidents has decreased from 49 per 100,000 population to 47.8 per 100,000 population, but the number of dengue deaths In 2021 there were 212 people with a CFR of 0.88, an increase from 0.72% in 2020.[10] Dengue fever is one of the seasonal/latent infectious diseases that if it is not anticipated well, it will have the potential to become an outbreak.DHF cases in West Java fluctuate every year.We can see of the data from 2017 to 2019.There were 11,422 cases in 2017, 11,458 cases in 2018, and 23,296 cases in 2019 with a total of 145 deaths.[11] [12] [6] In 2020, DHF cases have decreased from the previous year with 21,605 cases but the number who died was 150 people.[13] West Java Province is always included in the top 5 provinces with the most dengue cases.For example in 2020, West Java province ranks first with 18,608 dengue cases.[14] Various studies stated that the incidence of DHF cases influenced by climatic factors (temperature and humidity, rainfall and rainy days, vegetation, wind velocity, and duration of illumination) and geographical distribution (altitude, urban/rural).[15] [16] These two factors are the main key to the breeding of Aedes mosquitoes as infectious agent of DHF.Results of studies also showed that demographic factors such as population density, growth rate, mobility, and poverty are an integral part of the increased risk of dengue cases.[17] [18] Research on the dynamics of DHF transmission in the border areas of Mexico and the United States showed that the increase in cases in Mexico is influenced by the increased density of Dengue vectors in border cities of the United States, as well as demographic conditions in Mexico.[19] In Indonesia it has been reported that imported cases from border areas play an important role in the emergence of DHF outbreaks.[20] The results of this study provide an indication that every district/city in West Java has the potential to experience DHF outbreaks.This is because areas that are free/sporadic can experience re-emerging from the spread of cases from areas that are still endemic.This study aimed to analyze the relationship between rainfall, temperature and population density with the incidence of DHF in districts/cities of West Java Province.The results of this study are expected to provide input for policy makers, especially in West Java, in efforts to control vectors and early detect outbreak related to climate change and demographic factors.

Methods
This research was an analytic study.This used secondary data from 2017 to 2021 that included rainfall, temperature and population density data that was obtained from BPS Statistics West Java Province, and DHF case data that was obtained from the Health Office West Java Province.Because the data is not all complete, then given the treatment of the data.If rainfall/temperature data for one district/city is not IOP Publishing doi:10.1088/1755-1315/1239/1/0120233 available from 2017 to 2021, then that district/city is excluded from the analysis.If rainfall/temperature data for one district/city is incomplete (there are blank years) from 2017 to 2021, then those districts/cities are included in the analysis.For empty data of this condition, estimation is carried out by assuming the same conditions as the nearest year.Regarding the condition of variable data can be seen in table 1. Dengue fever is closely related to three factors, namely the host, vector and the environment other than the virus itself as the cause.[21] Finding of this study indicate that areas with denser populations (population density of more than 1,792 people/km) have an 8.75 times higher risk of experiencing DHF cases than areas with lower densities.This result corroborates that the population density of a community can determines dengue fever.Areas with a dense population are usually synonymous with slums.[22], inhabited by poor people and the housing conditions are usually inadequate.[23].High population density, accompanied with water supply, contributed greatly to the dengue epidemic.Dense urban areas especially in tropical environments make the environment ideal for dengue fever epidemics.[24] This is because an environment like this is conducive to the breeding of the Aedes aegypti mosquito.[22] Urban slum conditions with a dense population is often accompanied by limited availability of clean water.aside from that sewerage and inadequate waste management.The water shortages mean that 1239 (2023) 012023 IOP Publishing doi:10.1088/1755-1315/1239/1/0120235 people need to store water in large containers and this contributes to an increase in mosquito populations.[23] Dense populations are often synonymous with a dirty environment, such as dirty containers that are disposed of carelessly, creating a lot of stagnant water, which supports the breeding of the Aedes aegypti vector.[23] [24] Thus, densely populated areas which are usually supported by slum environments have great potential for breeding of the Aedes aegypti mosquito.
Finding of this study indicate that areas with high rainfall have the risk of increasing DHF cases is 21.43 times compared to areas with low rainfall.The results of this study are in line with Promprou et al. (2005), in a study of dengue haemorrhagic fever incidence rates and climatic factors in southern Thailand, showed that while climate variables (rain and temperature) did play a major role in the transmission cycle of dengue haemorrhagic fever, the importance of these factors differs by region.[25] The Andaman side with rainfall of 204 ± 215 mm and 80.85% humidity has the highest incidence of dengue haemorrhagic fever which is lower than the Bay side, which has 183 mm of rainfall and 79% humidity.[25] This variation is due to the high annual rainfall and higher number of rainy days on the Andaman Sea Side during the May to October monsoon season.[25] This finding contrasts with a previous study by Thammapalo, (2005) which concluded that the incidence of dengue haemorrhagic fever was similar in both regions.[26] Result of this study was also similar with some previous study that climate change included humidity, rainy days and rainfall influence the incidence of DHF cases.[27], [28] [29] [30] Thus climate change can affect the success or failure of efforts to fight DHF in the future.[28] Finding of this study show that there was not significant relationship between temperature and the incidence of DHF case (table 2).This is possible because in this study only distinguishes temperature in 2 categories, namely less than 27 degrees and more than 27 degrees by looking at the average monthly temperature thus daily temperature fluctuations do not appear.This is similar with research of Kesetyaningsih et al (2018) in Sleman District, Yogyakarta, Indonesia.[30] different studies found that temperature has an effect on the prevalence of DHF.[31] The results of this study indicate that regencies/cities in West Java with a population density of more than 1792.4people/km2, temperatures of more than 27º C and rainfall of more than 4800 mm/year have an 85.3% chance of having more than 2211 cases of DHF.Meanwhile districts/cities with a population density ≤1792.4people/km2, temperature ≤ 27 ºC and rainfall ≤ 4800 mm/year have a 96.4% chance of having DHF cases less or equal to 1474 cases.This confirms the hypothesis that the denser the population, the higher the rainfall and temperature, the greater the possibility of DHF cases occurring in the district/city.

Conclusion
Analysis of secondary data from 2017 to 2021 shows that there is a significant relationship between rainfall and population density and the incidence of DHF in West Java (p value 0.08 and 0.05).The analysis results also found that districts/cities with a population density more than 1792.40 have 8.75 greater probability of having DHF cases than areas with a population density less than or equal to 1792.40.Furthermore, districts/cities with rainfall above 4800 have a 21.43 greater probability to have DHF cases compared areas with rainfall less than or equal to 4800.This means that the denser the population and the higher the rainfall, the greater the chance of an increase in dengue fever.

Table 1 .
Variable data conditionData were analysed with ordinal linear regression which categorizes the variables as shown in table2.Based on this table it can be seen that DHF cases are said to be high if the number of cases more than 2211.Rainfall is high if it is more than 4800 mm, temperature is high if it is more than 27°C and the population is categorized as dense if it is more than 1792.4.

Table 3 .
The relationship of population density rainfall and temperature with the Incidence of DHF having DHF cases than areas with a population density less than or equal to 1792.40.Besides that, regions with rainfall above 4800 have a 21.43 greater probability to have DHF cases compared areas with rainfall less than or equal to 4800.3.2.Probability of DHF Cases inDistricts/Cities of West Java based on Rainfall, Temperature and Population Density Beside the Odds Ratio, ordinal regression analysis also produces probability of DHF case for each independent variable.The probability of DHF cases based on population density and rainfall variables is shown in the table 4.This table showed that districts /cities with population density < 1792.4,temperature < 27 and rainfall < 4800 have possibility for DHF cases < 1474 of 0.964 and DHF cases > 2211 of 0.015.On the contrary, districts/cities with population density > 1792.4,temperature > 27 and rainfall > 4800 have opportunity for DHF cases > 2211 of 0.853 and DHF cases < 1474 of 0.066.
The results of statistical analysis found that there were significant relationships between population density and rainfall with the incidence of DHF (p-value 0.018 and 0.005 respectively), but there was not significant relationship between temperature and the incidence of DHF (p-value 0.075).Results of ordinal regression analysis found that regions with a population density more than 1792.40 have an 8.75 greater probability of

Table 4 .
Probability of DHF cases in districts/cities of West Java based on rainfall, temperature and population density