Update From Expert Panel on Dengue

01 Oct 2005

Background

The panel was tasked to review the current dengue situation in Singapore; identify possible causes for the resurgence; identify gaps in dengue surveillance and control; recommend operational research to address the gaps identified and to recommend both short-term and long-term cost effective strategies in the prevention and control of dengue

The Panel has looked into the epidemiological features of the current dengue outbreak, conducted field trips to observe dengue control operations and reviewed the national framework for dengue control.

Key Observations

The key observations of the Panel are highlighted below:

- Singapore's dengue control programme is recognised as one of the best in the world. This has resulted in sustained suppression of the Aedes aegypti mosquitoes for three decades.

- Dengue is a resurgent problem globally; and being endemic to the region, Singapore can expect dengue to recur on a regular basis. The current dengue outbreak in Singapore coincides with the increase in the number of dengue cases in the region.

- The principal vector mosquito Aedes aegypti is highly adaptable and exploits hard-to-find habitats in the urban environment. The increase in the dengue cases in Singapore may include importation of new strains of dengue virus with greater epidemic potential into a densely populated Singapore population. Prior success of the Singapore dengue control programme has resulted in a highly susceptible human population. 

- Public education on dengue prevention and community participation in control activities remain the key to stop dengue transmission.

Recommendations

The Panel has recommended the following:

Short-term measures:

- Effective prevention and control of epidemic dengue requires an active laboratory-based disease surveillance programme to provide early warning for epidemic transmission. Laboratory methods should include the latest technology in both serologic and virologic diagnosis. Quality control for this programme should be provided by a national reference laboratory for infectious diseases. 

- A continuing medical education programme should be implemented to increase the knowledge of physicians on clinical diagnosis, management, prevention and control. They should be encouraged to help educate the population on their responsibilities in dengue control activities. Feedback of surveillance data to the medical community is important.

- It is a common perception that most dengue transmission occurs at home. However, recent epidemiologic evidence indicates that significant transmission also occurs at sites away from the home. Current emphasis on active clusters does not provide an adequate understanding of transmission dynamics. This limits the effectiveness of vector control measures, because in the present situation, it appears that 60-70% of all notifications occur outside of known clusters and in some instances transmission is not reported. Dengue control should be driven by entomological, epidemiological, operational and formative research, and should not rely solely on identification on response to active clusters. In addition, efforts to reduce mosquito population during inter-epidemic periods may be highly effective in preventing epidemic transmission. 

- The success of the Singapore programme has reduced Aedes aegypti populations to such a low level that conventional methods of assessing populations such as the House Index are no longer sufficient. Moreover, an increase in Aedes aegypti populations is not always a pre-requisite for increased dengue transmission. Emphasis should now be placed on new and innovative methods of entomologic surveillance to assess the impact of control activities on Aedes aegypti populations. For example, ovitraps and/or lethal ovitraps developed by NEA and others will be used to detect and eliminate low-density Aedes aegypti populations in various settings. 

- Feedback to the community on mosquito populations should be explored as a mechanism to stimulate community participation in control activities.

- Continued efforts to enhance dengue control by the private sector should be emphasized, including social mobilisation and mosquito control. For example, the NEA programme to create community ownership of the control programme by town councils contracting to the private sector is strongly endorsed by the committee. 

- Indoor fogging may be very effective in killing adult Aedes aegypti. However, recent evaluation of this approach to stop epidemic transmission, as practiced by many dengue-endemic countries, has revealed that it has limited efficacy in stopping epidemic transmission. The effectiveness of ultra-low volume and thermal fogging to control adult Aedes aegypti must be evaluated. Mosquito control activities, including those by private pest control operators, must continue to be subjected to stringent and improved quality control measures using new techniques. 

Long term measures

- Maintain Aedes aegypti populations at a low level in Singapore that will prevent epidemic dengue transmission. 

- Use vaccines and antiviral drugs when they become available. 

- Use new validated technologies as they become available.

What the public can do

- Effective long-term control of dengue requires community ownership. Therefore community participation will continue to be an important component of effective Aedes aegypti control in Singapore. 

- The inclusion of grassroots organisations in surveillance of adult mosquitoes, e.g. by lethal ovitraps, should be explored. 

- Regular indoor use of insecticide sprays may prevent dengue transmission in the home.

- Use of personal protection measures such as repellents and mosquito nets may also prevent dengue transmission in the home.

The Panel has also examined the need to quarantine dengue patients and biological control methods. Their conclusions as follows: 

- Quarantine of dengue patients is not recommended. Infected people can infect mosquitoes with dengue viruses 24 - 48 hours before showing any symptoms. Infected people, who do not show any symptoms (asymptomatic cases), may also infect mosquitoes. With Singaporeans being highly mobile and the local dispersal of mosquitoes, the virus may be widespread in the community before it is reported.

- Biological approaches to mosquito control eg, fish, dragonflies, copepods are also not applicable in the Singapore environment.

Conclusion

The Government has noted the findings and recommendations of the Panel and will review them. We will continue to work with the Expert Panel on improving our dengue control programmes.

As pointed out by the Expert Panel, community involvement is key to dengue control in Singapore. We would like to urge the public, business/industry stakeholders to continue to be vigilant in keeping their premises, workplaces and surroundings clean and mosquito-free by practicing good habits. These include cleaning blockages from the roof gutter, clearing leaves and stagnant water from potted plants, avoiding the use of pot plates, changing the water in vases daily and keeping the environment litter-free.

View the Report of the Expert Panel on Dengue.