incidence surged again on January, a month after the rainy season starts or the peak of rain precipitation( figure 1).
Meanwhile, the pattern of death case caused by DF showed different pattern than in figure 2. In figure 4, the death case caused by DF happened mostly on the same month when the DF incidence rose( January 2012, 2013, and 2016). The difference is caused by the high death case on February 2015 which, in total, made the death case seemed to happen mostly in February.
IV. Discussion
Dengue’ s infection relied heavily on its vector. Therefore, everything that affects the vector( survival rate, epidemic potential, reproduction rate, etc) would also affect the spread of the virus. As elaborated in the introduction, there are three main environmental parameters that has been proven to affect dengue infection: temperature, humidity, and rainfall [ 8-13 ]. These factors would affect the mosquito’ s survival probability and its epidemic potential.
Out of the three main parameters, data regarding historical humidity at Sampang were not found but data on temperature and rainfall were acquired from literature search( Figure 1). For temperature, we can see that the monthly temperature at Sampang is comparable and consistent with little difference throughout the year( figure 1). Therefore, the effect of monthly variation of temperature on DF incidence may be ignored. Meanwhile, rain precipitation differed throughout the year. Rain precipitation gradually decreases from January to August. Rising significantly from September until reaching its year’ s peak at December.
From figure 2, the result on this research is consistent with the theory which stated that an increase in rain precipitation is equivalent to the increase in DF cumulative incidence with a time gap approximately 24-30 days [ 8 ]. By comparing figure 1 and figure 2, peak of rain precipitation and DF incidence had 1 month delay. This result is as proposed by Carrington and Simmons [ 8 ] and the study conducted by Lu et al in Guangzhou [ 10 ] which says that there will be approximately 1 month of time gap after the rainy season( indicated by rise in rain precipitation) before the incidence of DF rises. Meanwhile, death case peaked at January, the same month the DF incidence peaked, except on February 2015. Other studies have found that there is 5-8 days of delay from symptom onset to mortality [ 26, 27, 28 ]. This explains the difference in death case peak on other years compared to 2015. If the DF incidence surged during the last week of January then the death case will accumulate on February.
We also like to point out that there is an increase in incidence over the years from 2012-2015 which we can look in Figure 3. Other studies evaluating the incidence of DF infection between 2012-2015 also showed an increasing trend of dengue incidence and DF in Asia County with tropical climate( e. g. Malaysia) and subtropical climate( e. g. Japan) [ 29, 30 ]. The increase in temperature might contribute to this increase over the years. Globally, due to global warming, data from NASA [ 31 ] showed an increase of 37 % in global temperature index from 2012-2015. Nationally, there are no historical data about Indonesia’ s or Sampang’ s temperature increment but Hulme and Sheard [ 19 ] predicted Indonesia’ s temperature will increase by 0.3 o C annually. Rainfall might also attribute to the increase but more data is needed to affirm this especially data about temperature and rain precipitation yearly differences in Sampang.
Our data also showed that there is relatively no difference in the pattern of monthly DF incidence each year. Although the number of DF incidence may differ from year to year, which may be caused by the climate and weather change, but the pattern of DF incidence is similar in the last 5 years. The data showed that the highest peak of DF incidence always happened on January and gradual decrease on each month after. Reaching the lowest around August and November, which is consistent with the end of dry season and the transition month( October and November)( see Figure 1. for monthly rainfall index in Sampang regency). Out of this, it is necessary for the