doi:10.4269/ajtmh.12-0150 Copyright © 2013 by The American Society of Tropical Medicine and Hygiene Short Report: High Rates of Inapparent Dengue in Older Adults in Singapore

Abstract. Although the dengue iceberg phenomenon is well known, there is a paucity of data on inapparent dengue. Results from a seroepidemiological study conducted during a dengue epidemic in 2007 in Singapore showed a seroprev-alence of 65.9 % and an inapparent dengue rate of 78%. Older adults (> 45 years old) had significantly higher rates of inapparent dengue infections (P < 0.05). Since the first report of a dengue epidemic in 1901, Singapore has had outbreaks of dengue fever (DF). Unlikemany countries in the region, dengue cases in Singapore are largely reported among the adult population,1,2 and dengue mortality is mainly observed in adults.3 Dengue infection is often epitomized by the iceberg effect, in which most cases are clinically inapparent.4 Although inapparent dengue has been reported in many coun-tries,5–7 there is little data on its epidemiology or the extent of its severity. During the dengue epidemic in Singapore in 2007, we conducted cross-sectional seroepidemiologic surveys in seven outbreak areas (Figure 1) to estimate the dengue attac