NEA outlines dengue control measures

PHOTO: NEA outlines dengue control measures

SINGAPORE - We thank the various Forum writers for their ideas on dengue control.

We agree that a multi-pronged approach is necessary. The integrated dengue control programme incorporates early warning of outbreaks, consistent mosquito reduction and active cluster management to stop transmission. A key objective is to deprive the Aedes mosquito of breeding habitats.

Less than 1 per cent of premises have been found to be breeding mosquitoes during National Environment Agency (NEA) checks. This has been a protective factor against major outbreaks for the past six years. Paradoxically, it has also lowered our population's herd immunity.

The current outbreak is due to a change in the serotype of the prevalent dengue virus with a high epidemic potential. Therefore, even slight changes in Aedes prevalence will amplify infection rates.

In areas with ongoing transmission, both source reduction and the killing of adult mosquitoes are essential.

While some studies do not support the use of outdoor fogging, our experience shows that indoor ultra-low-volume misting is beneficial as the Aedes aegypti mosquitoes prefer to remain indoors.

The NEA's Environmental Health Institute (EHI) has been deploying Gravitraps to lure and trap adult mosquitoes since last year, instead of the older ovitraps that target only mosquito eggs and larvae ("Adopt new ways to fight dengue" by Ms Dawn Kua Su-Wen, June 20; and "Map out new line of attack" by Mr Ronnie Lim, Tuesday).

We conduct epidemiological investigations to trace the movement history of dengue patients so as to pinpoint the likely sources of dengue transmission.

We classify an area as a dengue cluster when the workplaces or residences of two or more patients, whose fever onset dates are within 14 days of each other, are less than 150m apart.

However, many people with mild dengue infections remain undiagnosed but still act as a reservoir of infection when mosquitoes are present. Hence, not all cases can be traced to defined clusters.

Consequently, we have been using breeding data to identify other higher-risk areas ("Redefine dengue clusters" by Mr Loh Kwek Leong, June 14; and "Highlighting dengue clusters may breed false sense of security" by Miss Ng Swee San, Forum Online, June 19).

We agree that protecting patients from mosquito bites will help break the transmission cycle ("Shield dengue victims from mosquitoes" by Mr Chang Yue Chang; June 19). Application of repellents, the use of mosquito nets or staying in a mosquito-free environment are useful measures.

The Health Ministry and the NEA are distributing mosquito repellents to all households.

The EHI has been providing subsidised tests to primary health-care clinics since 2006 ("Supply dengue test kits to GPs" by Dr Leong Choon Kit; June 15). This has enabled earlier diagnosis and improved vector control measures.

The EHI is assessing novel technologies using sterile or infection-resistant mosquitoes. Field trials will be done only if safety is established.

We agree that everyone, and not just those in dengue clusters, needs to take precautions. We need all to do their part to protect our families and neighbours.

Derek Ho
Director-General Public Health
National Environment Agency

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