Shift in the transmission pattern of dengue serotypes and concurrent infection with more than one dengue virus serotype.

All four serotypes of dengue have been cotransmitting in the country for many years [2]. However, they do not occur in equal abundance. In a series of 477 dengue tests done in Colombo in 2007, among 55 positive detections, the serotypes detected were DEN-1 in 1 (1.8%); DEN-2 (dengue virus serotype 2) in 25 (40.0%), and DEN3 in 19 (34.5%). DEN-4 (dengue virus serotype 4) was not detected. The serotype could not be determined in 9 (16.3%) [3]. It is well known that shifts in the relative abundance of serotypes could result in dengue outbreaks.