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