Dengue--old disease, new challenges in an ageing population.

1Department of Infectious Diseases, Singapore General Hospital 2Program in Emerging Infectious Diseases, Duke-NUS Graduate Medical School Address for Correspondence: Dr Jenny Low, Department of Infectious Diseases, Singapore General Hospital, Outram Road, Singapore 169608. Email: [email protected] Singapore has experienced yet another epidemic. With more than 13,000 cases reported as of mid July 2013, this could possibly be one of the worst outbreaks in Singapore’s history. Dengue claimed its fi rst death in May this year and since then, 4 others have died of dengue. Of these 5 deaths, 80% occurred in patients older than 60 years. The last epidemic from 2004 to 2005 saw more than 14,000 cases with 27 reported deaths. The median age of death cases then was 59.5 years.1 Mankind has been living with the dengue disease from as early as the Jin Dynasty (265 – 420 AD) period when the fi rst case of probable dengue was recorded in a Chinese medical encyclopedia.2 In the last 50 years or so, we have witnessed an unprecedented expansion in the geographic distribution of epidemic dengue globally. This expansion is facilitated by unplanned and rapid urbanisation in many tropical and subtropical countries, modern trans-national transportation, lack of effective mosquito control and globalisation at a rate that we have not experienced before. Dengue is currently considered by the World Health Organization (WHO) to be one of the most important infectious diseases affecting tropical urban areas in the 21st century. The latest estimate is that nearly 400 million people are infected with dengue each year with a quarter of these presenting with acute illness.3 Besides the geographic expansion of dengue, the epidemiology of dengue has also been changing. The modal age of disease presentation has also been increasing over the more recent decades. When epidemic dengue emerged in Southeast Asia after the Second World War, it was predominantly a paediatric disease.4 However, since the 1980s, there has been an increasing incidence of dengue reported among adults from many parts of the tropics and subtropical countries. Multiple factors have contributed to this trend. In Singapore, the increase in age of dengue cases is likely to be caused by the reduced vector population and hence transmission intensity.5,6 Rural to urban migration of adults seeking employment and other economic activity has also raised the age of the population susceptible to dengue infection. At the same time, the world’s population is rapidly ageing. Between 2000 and 2050, the proportion of the world’s population over 60 years will double from about 11% to 22% with the absolute number expected to increase from 605 million to 2 billion over the same period.7 According to Singapore’s statistics, by 2050, 38% of our