The mean age of dengue-affected cases in this study was
22.1 years; this finding of adults being affected by DF/DHF is in
agreement with the data obtained from recent Sri Lankan studies.
In the past DF/DHF was primarily a paediatric disease in Sri Lanka,
however there has been a shift in the affected age in the last 8 years
(mean 22–25 years).3,14,16 Adults of both genders, either going to
office jobs or working in the house premises or paddy fields might
be exposed to daytime biting mosquitoes. In contrast to adults,
infants mainly stay inside the houses during the daytime and thus
are protected from these mosquitoes. The staff of schools in Jaffna
District are well educated in taking measures to prevent dengue
mosquito breeding, hence the school children rarely acquire the
infection during the daytime. These reasons might explain the
higher number of cases among adults than children in the study
area. On the other hand adults may have immunity to a particular
type of DENV and these adults when infected with a second type of
DENV would become symptomatic, in contrast to children with
primary infections, again contributing to the increase in DF/DHF
cases in adults.