High potential risk of dengue transmission during the hot-dry season in Nha Trang City, Vietnam.

We visited houses and inspected water-holding containers to determine the potential risks of dengue transmission during different seasons. This survey was conducted in two neighbourhoods of Nha Trang City in July and December 2006, which correspond to the middle of the hot-dry season and the beginning of the cool-wet season, respectively. We inspected a total of 1438 wet containers in 196 premises during both survey periods; 20% of the containers were positive for Aedes aegypti larvae and 8% for A. aegypti pupae. Indoor water-holding containers, which were sparsely distributed, exhibited high pupal productivity and efficiency (pupal productivity of a type of container/prevalence of that type of container) in either the first survey conducted in July, or the second, conducted in December. Although rainfall may not influence the number and distribution of water-holding containers in the city, the high average temperature in the first survey period resulted in a higher potential risk of dengue transmission. Our analysis suggests that if intensive source reduction is conducted in summer and containers with high pupal productivity and efficiency are targeted, the risk of dengue transmission in the city could be effectively reduced.