MANILA, Philippines ? The Department of Health appealed Thursday to private contractors to rid construction sites of possible breeding sites of dengue-carrying mosquitoes, as the number of dengue fever cases in Metro Manila more than doubled.

National Epidemiology Center director, Dr. Enrique Tayag, said the number of dengue cases in Metro Manila reached 8,386 as of Aug. 23, compared to only 3,106 about the same time last year.

Dr. Yolanda Oliveros, director of the National Center for Disease Control and Prevention, said they were coordinating with the Metropolitan Manila Development Authority in encouraging construction companies not to leave their projects idle for a long time.

?If they cannot work on excavations immediately, they should fill them up in the meantime (instead of leaving them open),? Oliveros said.

Metro Manila has the highest number of cases so far, followed by Central Luzon with 2,719 cases and Central Visayas with 2,352 cases as of Aug. 23, Tayag added.

Oliveros said Metro Manila recorded more dengue fever cases than other areas in the country not only because it is heavily populated, but also because of many construction projects in the area that provide breeding grounds for mosquitoes.

Dengue fever is transmitted by mosquitoes that bite during the day, breeding in stagnant water. The DOH said in its website that dengue fever ?is preventable but is prevalent in urban centers? with high population density and inadequate water supply, solid waste collection and storing.

Tayag assured the public there were no outbreaks in any areas in the country, although four barangays in Metro Manila have been declared as hotspots. These are barangays Baesa and Batasan Hills in Quezon City, Barangay Parang in Marikina City and Barangay 177 in Caloocan City.

Three barangays outside Metro Manila were also declared as hotspots: Labangon in Cebu City, Marigondon in Lapu-Lapu City and Looc in Danao City.

But all over the country, the number of dengue fever so far this year is slightly lower compared to the same period last year. There are 24,794 dengue cases as of Aug. 23, compared to 28,431 cases reported the same period last year, Tayag said.