Advisory Council on Food and Environmental Hygiene

Situation Report on Dengue Fever in Hong Kong

PURPOSE AND ADVICE SOUGHT

This information paper presents the dengue situation and control strategy in Hong Kong and seeks Members' views on -

  • the control measures; and
  • whether additional measures should be adopted.

BACKGROUND

2. Dengue fever is a viral illness transmitted by the bite of infective mosquito. It is not directly transmitted from person to person. There is no effective vaccine.

3. In Hong Kong, dengue fever has been made statutorily notifiable since 1994. Between 1994 and 2001, the annual number of notifications ranged from 3 - 17 cases; all these cases acquired the infection from outside Hong Kong (i.e. imported cases), mostly from South East Asian countries. As at 10 Oct, there were 36 confirmed cases, including 16 imported cases and 20 local cases. There have not been any fatal cases reported.

4. According to laboratory test results, one confirmed local case was of serotype 2 virus while the 19 other local cases were caused by serotype 1 Dengue virus with identical genetic sequences. The sources of these viruses are still uncertain. It also remains uncertain whether the serotype 1 virus has spread from Ma Wan to Cheung Sha Wan and Tsuen Wan, where two isolated cases have been identified.

5. The control strategy comprises:

  • Early case detection, prompt treatment and laboratory confirmation
  • Epidemiological surveillance
  • Entomological surveillance and mosquito control
  • Regular territory-wide anti-mosquito campaigns to eliminate breeding sites and encourage community participation
  • Community publicity efforts to educate the general public to adopt preventive measures
  • Health advice to travellers on the prevention of mosquito bites and the awareness of the symptoms of dengue fever.

6. All notified cases are investigated for the source of infection, the risk of local spread is assessed, and control actions are undertaken to prevent secondary spread. Investigation and control actions are conducted jointly by the Department of Health (DH) and the Food and Environmental Hygiene Department (FEHD).

7. In 2001, the DH set up the Interdepartmental Coordinating Committee on Dengue Fever to keep under review the prevention and control strategies, coordinate education and publicity efforts, and coordinate implementation of contingency measures by government departments and Hospital Authority necessary for the control of dengue fever in Hong Kong.

8. On vector control, regular inspections and disinfestations works are carried out by FEHD throughout the year. We also monitor closely the breeding of Aedes albopictus, the mosquito vector which is capable of transmitting dengue fever virus, so that we can adjust our mosquito control strategy accordingly. The effective control of mosquito problem requires collaborated efforts of the whole community. Anti-mosquito campaign is therefore organized on a territory-wide basis annually to encourage community participation and to promote concerted efforts of various government departments in mosquito prevention and control work.

9. With experience gained in 2001 and in view of the dengue fever outbreak in Macau, the 2002 anti-mosquito campaign is conducted in three phases starting from April 2002 with an additional phase introduced in May-July 2002 to sustain the anti-mosquito efforts. Areas favouring the harbourage of mosquitoes or in close proximity to human activities such as schools, construction sites, housing estates and hospitals are areas of target control. Apart from carrying out intensified inspection and disinfestation works during the campaign period, we have made use of a wide range of promotional channels to encourage community participation in our campaign as well as organizing various activities to arouse people's awareness and to give them useful advice on how to prevent mosquito problems.

LOCAL DENGUE CASE

10. The first local dengue fever case was confirmed on 21 Sep 2002, and subsequent investigation by the DH confirmed that the source of infection was in Ma Wan. Through active case finding among the workers and residents in Ma Wan, hotline enquiries and hospital notifications, further cases related to Ma Wan were identified. As at 10 Oct 2002, there were a total of 16 cases related to Ma Wan, including 10 workers and 6 residents, and they had disease onset between 19 Jul and 24 Sep 2002.

11. On 29 Sep 2002, dengue fever was confirmed in another patient who has neither gone to Ma Wan nor travelled outside Hong Kong during the incubation period. He might have contracted the disease while fishing in places around the Fish Marketing Organization (FMO) Market in Cheung Sha Wan.

12. On 3 Oct and 4 Oct 2002, another two patients who live in Tsuen Wan and Sham Shui Po were confirmed to have contracted dengue fever locally.

13. On 9 Oct, one patient who received blood during an operation in hospital was confirmed to have contracted dengue fever. The blood was given by one of the Ma Wan residents infected with the disease before symptoms developed.

Control measures for the local outbreak

Disease surveillance

14. Field visits to residential and work places of all patients were made by the DH and FEHD staff for health education, active case finding and prompt vector control.

15. DH has also set up a hotline for counselling and screening of persons who have lived or worked in Ma Wan, for workers around the FMO Market in Cheung Sha Wan and residents in Tsuen Wan and Sham Shui Po.

16. All public general outpatient clinics and the Hospital Authority have been informed of the management of these at-risk individuals. A letter to all registered medical practitioners was sent on 24 Sep 2002 to inform them about the local outbreak and to remind them to notify suspected or confirmed cases of dengue fever to DH early.

17. Health education and medical surveillance of the household members of the cases were also conducted.

Inspection /Disinfestation Works by FEHD

18. Since the first local case was confirmed, FEHD staff have carried out extensive mosquito control operations in venues connected with the dengue fever cases and other high risk areas for mosquito infestation. A total of 575 construction sites were inspected on 23-24 September, resulting in the issue of 86 summonses and 36 warnings. The problematic sites were inspected again on 30 September. Nine further summonses were issued. Starting from 25 September, inspections have been extended to densely populated areas like housing estates, schools and hospitals.

Public education

19. The public have been kept informed of the dengue situation through a series of joint press conferences by DH and FEHD, media interviews and daily updates issued by the DH to the media.

20. Through the Announcement of Public Interests (API) in radio and television, health education hotlines, website information, health talks, pamphlets and posters, the public are reminded of the necessity for elimination of mosquito breeding places and precautions against mosquito bites both in Hong Kong and while travelling outside Hong Kong. Roving exhibitions at major shopping malls, outreaching health talks for schools, construction site management and workers are also being conducted to drive home the message.

21. Various other departments have joined DH and FEHD in the territory-wide anti-mosquito operations. For example, the relevant Government Departments have strengthened anti-mosquito measures in public premises such as country parks and recreation and sports centres. Inspection, waste removal and grass-cutting for unallocated Government land has been stepped up. The Education Department has reminded all schools to take necessary preventive measures against mosquito breeding and the Information Services Department has intensified broadcasts of TV and radio APIs on mosquito prevention and control.

Anti-mosquito Steering Committee (���A�w���ɩe���|)

22. Apart from escalating territory-wide anti-mosquito efforts, we saw a need to map out a comprehensive strategy and set directions from anti-mosquito work. We also believe that it is crucial to involve the community and private sector in and to maintain public alertness to the importance of sustained anti-mosquito efforts. We have therefore established the Anti-mosquito Steering Committee, which comprises senior officials from a number of policy bureaux and Government departments, to oversee strategy and direction setting and to seek to increase the involvement of the community and private sector. The first meeting of Steering Committee was held on 10 October 2002. Some of the more major actions the Committee decided to take in addition to the actions already taken as described in the preceding paragraphs are as follows -

Vector surveillance and control

  • FEHD will review the distribution of ovitraps to ensure that they are all strategically located and increase their numbers.

  • From early 2003 onwards, FEHD will make public the mosquito breeding index - the percentage of ovitraps found to have larvae laid - on a monthly basis. This will enable members of the public to learn about the risk of mosquito bites at different times of the year.

Disease Surveillance and Control

  • DH will keep all medical professionals up-to-date on the latest developments of the disease through bulletins, letters and the Internet, while close monitoring and laboratory testing and other diagnostic work will continue. All medical professionals are required by statute to report suspected and confirmed cases in a timely manner already.

  • DH will step up liaison with the World Health Organization and overseas health authorities with a view to enhancing the effectiveness of the preventive and control measures adopted locally.

Community involvement and raising public alertness

  • Government departments concerned will extend this year's anti-mosquito campaign into winter.

  • The Home Affairs Department (HAD) will approach Owners' Incorporations and Mutual Aid Committees to seek their co-operation in the anti-mosquito drive, targetting at keeping common parts of buildings clean and proper refuse management.

  • HAD will seek the Clean Hong Kong District Promotion Committee's endorsement of the setting up a working group to actively involve the District Councils and other district organizations in the territory-wide anti-mosquito exercise.

  • FEHD and DH will jointly conduct community-based surveys to assess public awareness and behaviour on dengue fever and mosquito prevention. Such surveys will help us adjust our control measures from time to time.

  • For the convenience of the public, a one-stop, dedicated hotline run by FEHD will be set up to provide advice on mosquito control and handle public enquiries.

Government actions and targets for the coming few months

  • The FEHD will complete within three weeks a round of inspection to common parts of private tenement buildings such as roof top and light well to eliminate potential mosquito breeding grounds. Another reound will be conducted before the Lunar New Year as part of the year end clean-up.

  • The Leisure, Cultural Services Department (LCSD) will deploy a special cleansing team to carry out focused anti-mosquito operations twice a week at selected venues.

  • The Lands Department will complete two rounds of grass cutting and rubbish clearance on identified black spots covering more than 250 sites by February 2003.

  • The Agricultural, Fisheries and Conservation Department (AFCD) will launch a Clean Country Parks Scheme 2002. A 13-week intensive clean-up operation for all country parks will begin in this month.

  • The Highways Department will step up inspections on all roadwork sites, roads/drains, road slopes, highway structures and depots to eliminate mosquito-breeding places.

  • The Environmental, Transport and Works Bureau will make mosquito control an agenda item in all Site Safety Committee Meetings to discuss the effectiveness of measures taken.

CONCLUSION

23. These anti-mosquito efforts have to be sustained to reduce the risk of dengue fever in the coming years. We will be consulting Members on the control strategies from time to time to develop the most appropriate measures to meet the challenge.

Department of Health
Food and Environmental Hygiene Department
Health, Welfare and Food Bureau

October 2002

 

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