Relationship of aedes indices and dangue cases in Tawau: a ten year study / Amnah Bayani

Dengue is currently the most important vector-borne disease globally – Malaysia is one such nation witnessing an increase of dengue incidence over the years. Entomological surveillances using Aedes indices (House index, Breteau index and Container index) is used to decide changes in the topographical dissemination and abundance of the vector, assess control programs, get relative estimations of the vector populace and encourage proper choices with respect to intervention. This study conducted was to assess whether there is any relationship between the Aedes indices and dengue incidence in Tawau, Sabah. A retrospective cohort study was conducted in this study. Ten years of data was collected from the Vector Control Unit, Tawau – dengue cases and Aedes indices reported in Tawau from 2008-2017. The dengue trend in Tawau was analysed descriptively using Microsoft Excel 2010. Subsequent analysis was then carried out on the data- testing correlations between the variables and their lags, prior to developing a regression model to further test the relationship between these variables. We observed the dengue trend in Tawau and found a fluctuating but generally upwards trend in dengue incidences. On the other hand, the Aedes indices have fluctuating trends over the study period but generally exhibited an increase as the year progresses. When these data were tested for correlation using the Spearman Rank test, several explanatory variables demonstrate a weak relationship with dengue cases over the period of 2008-2017, namely - House Index at a Lag of 6 weeks (r=-0.167), Breteau Index at a Lag of 1 weeks (r=0.062) and container index at a Lag of 1 weeks (r=0.210). In general, these variables prove to have no direct relationship with dengue cases. These variables were then further tested for a relationship using a Poisson regression distribution, of which all variables proved to have no significant relationship (p-value>0.5). Through this study, it has been showed that vector surveillance data cannot be consistently used to evaluate dengue transmission in Tawau. Dengue cases still occur at low Aedes indices and this may be due to other covariates such as: - environmental conditions, populations density, diaspora, travelling waves,infrastructure available, rate of urbanization, vegetation index and possibly other factors may all play a coercive role in the transmission of dengue. Further study is required by all relevant parties, and a concerted push must be made to develop a more relevant and significant means of quantifying the magnitude of dengue transmission in Tawau- and as an extension, Malaysia.