“Dengue always felt like a ‘it will happen to someone else but not me’ kind of thing, so it was a huge shock to find out that I had this virus,” said Ms Poh, a communications executive.' The experiences of Ms Poh and Mr Toh reflect just how enigmatic dengue fever can be — almost impossible to trace and at times, tricky to diagnose, and hard to guard against. The dengue virus also has four known strains or stereotypes. While infection with one strain appears to provide immunity against that one stereotype, evidence points towards increased risk of severe symptoms upon subsequent infections by the other three strains. The existence of these strains is one reason why dengue continues to be a perennial problem, especially in places like Singapore, whose tropical climate — abundant rainfall, high humidity and temperatures — creates an ideal breeding ground for mosquitoes. Despite stepped-up inspections and having a predictive model to help forecast dengue incidence, our national pre-emptive response to impending dengue outbreaks appears to have limited effectiveness.