The Association Between Climatic Factors and Dengue Fever: A Study in Subang Jaya and Sepang, Selangor

Background and Context

Dengue fever is one of the most dangerous and widespread vector-borne diseases globally, and Malaysia has experienced a particularly severe and escalating burden. Caused by virus serotypes DEN-1 through DEN-4 and transmitted through the bite of infected Aedes mosquitoes (primarily Aedes aegypti and Aedes albopictus), dengue has been endemic in Malaysia for decades. However, the scale of the problem has grown dramatically: cases rose from approximately 6,000 in 1995 to over 40,000 in 2010, with the trajectory continuing upward. In 2014, the situation became particularly alarming, with 108,698 notified cases reported by year’s end—an increase of 151 per cent compared to the 43,346 cases recorded during the same period in 2013.

Selangor state has consistently been the highest contributor of dengue cases in Malaysia, owing to its dense urbanisation, large population, and extensive construction activity that creates ideal mosquito breeding habitats. Understanding the environmental determinants of dengue transmission is critical for developing effective early warning systems and targeted vector control strategies. This study examined the relationship between three key climatic variables—temperature, rainfall, and humidity—and the prevalence of dengue fever in two contrasting districts within Selangor: Subang Jaya, a densely populated urban area, and Sepang, a less urbanised district.

Study Design and Methods

The researchers employed a comparative ecological study design, analysing dengue case notification data alongside meteorological records from both Subang Jaya and Sepang districts. Dengue case data were obtained from the respective health district offices, while climatic data—including daily and monthly records of temperature, rainfall, and relative humidity—were sourced from the Malaysian Meteorological Department. Municipal council records from both Subang Jaya and Sepang provided supplementary contextual data.

Statistical analyses were conducted using SPSS Version 20. The primary analytical approach was a general linear model (GLM), which was used to investigate the relationship between the three climatic variables and monthly dengue fever case counts. This approach allowed the researchers to assess the independent contribution of each climatic factor while accounting for the influence of the others. The study period covered sufficient months to capture seasonal variation patterns.

Key Results

The general linear model analysis revealed that rainfall and humidity were both significantly associated with monthly dengue fever cases. Rainfall emerged as the most significant predictor (p < 0.001), which is biologically plausible given that rainfall creates and replenishes the standing water collections in which Aedes mosquitoes breed. Discarded containers, construction sites, clogged drains, and other man-made water-holding receptacles—all common features of urbanised Malaysian environments—become active breeding sites following rainfall events.

Humidity also showed a significant positive association with dengue cases (p = 0.002). Higher relative humidity has been associated with increased Aedes aegypti feeding activity, improved mosquito survival, and accelerated egg development—all factors that can amplify the vector population and, consequently, disease transmission potential.

Temperature, somewhat surprisingly, was not significantly related to monthly dengue cases (p = 0.561) in this study. The authors noted that this null finding may be attributable to the relatively short study period and the limited temperature range variation in Malaysia’s equatorial climate, where mean temperatures remain fairly constant throughout the year. Previous systematic reviews of climate–dengue research in Malaysia have noted that the evidence for a direct temperature effect has been inconsistent across different study designs and locations.

The comparative analysis between the two districts revealed substantially higher dengue prevalence in Subang Jaya compared to Sepang. This difference was attributed to Subang Jaya’s considerably higher population density and more extensive urban development, which provide both more potential breeding sites and a larger susceptible human population in close proximity to vector habitats. This finding underscores the role of urbanisation as a critical modifier of the climate–dengue relationship.

Significance Within Malaysian Dengue Research

This study contributes to a growing body of evidence on the relationship between climate and dengue transmission in Malaysia. A systematic review of climate–dengue research in Malaysia found that temperature, rainfall, and humidity were the most commonly studied climate variables, with most studies concentrated in Selangor and Penang states. The present study’s finding that rainfall is the dominant climatic predictor aligns with multiple other Malaysian studies, including research in Bandar Baru Bangi and analyses using satellite-based Earth Observation data.

The study also reinforces the importance of considering urbanisation dynamics alongside climatic factors. While climate provides the environmental conditions conducive to vector breeding and survival, the intensity of dengue transmission in a given area is heavily modulated by human population density, land use patterns, waste management practices, and the availability of man-made breeding sites. This has important implications for dengue prediction models, which should ideally incorporate both climatic and demographic variables.

Implications for Public Health Practice

The findings support the integration of rainfall and humidity data into dengue early warning systems in Malaysia. During periods of heavy rainfall, public health authorities could intensify vector control activities, community clean-up campaigns, and public awareness messaging. The significant role of urbanisation suggests that dengue prevention must be embedded in urban planning and development approval processes, with mandatory requirements for construction sites to manage standing water and for new developments to incorporate mosquito-resistant design features.

At the community level, the results reinforce the importance of eliminating standing water around homes, particularly after rain events. The Malaysian Ministry of Health’s existing dengue prevention campaigns, including the “10 Minutes of Search and Destroy” initiative, are supported by this evidence linking rainfall to breeding site availability.

Limitations

The study has several important limitations. The relatively short study period may have been insufficient to capture the full complexity of climate–dengue dynamics, including potential lagged effects of climatic variables on mosquito population dynamics and disease transmission. The ecological study design, analysing aggregate data at the district level, cannot account for individual-level variation in exposure or susceptibility. The null finding for temperature should be interpreted cautiously, as other studies with longer time series have detected significant temperature effects in Malaysian settings. Additionally, the study did not account for other potentially important variables such as population immunity (herd immunity), circulating serotypes, vector control interventions implemented during the study period, or land use changes.