For discussion on                                                ACFEH Paper 52

8 July 2004



Advisory Council on Food and Environmental Hygiene


Anti-mosquito efforts made by the Government





              This paper briefs Members on measures taken by the government to guard against mosquito-borne diseases in the light of the recent rise in ovitrap indices in the territory and reports on the progress made thus far.


Dengue Fever in Hong Kong


2.            Hong Kong is geographically surrounded by dengue-endemic countries in Southeast Asia, and the dengue vector mosquito Aedes albopictus is widely found in Hong Kong.


3.            Dengue fever (DF) has been made statutorily notifiable in Hong Kong since 1994.  The annual number of notifications ranged from 3 �V 49 cases (median: 10).  There were no fatal cases.


4.            All notified cases were investigated for the source of infection, the risk of local spread was assessed, and control actions were taken to prevent secondary spread.  Most of the cases were imported, mostly from Southeast Asia.


Situation in 2004


5.            As of 21 June 2004, a total of 14 imported DF cases were reported to the Department of Health (DH).  Twelve cases were imported from Southeast Asian countries {Thailand (3), Philippines (2), Indonesia (4), Malaysia (1), Singapore (1) and Cambodia (1)}, one case imported from South Asian countries {Sri Lanka (1)} and one case imported from South Pacific countries {Tahiti (1)}.  The patients of all 14 cases had recovered.  The situation is similar to 2003, when most of the 49 cases reported were imported cases mainly from Southeast Asia.


6.            The local DF outbreak in 2002, together with the record high number of imported cases in 2003 and the number of cases reported to DH in 2004 so far indicate that, given the intense population movement among Hong Kong and other countries, particularly the dengue-endemic countries in Southeast Asia and the widespread prevalence of DF vector mosquito in the local territory, the risk of DF transmission giving rise to local case is still present.


Mosquito Surveillance


7.            Since 2000, the Food and Environmental Hygiene Department (FEHD) has put in place a surveillance programme to monitor the distribution of Aedes albopictus, the vector of the Dengue virus, at selected locations, evaluate the effectiveness of mosquito prevention and control work carried out by various parties, and provide surveillance information for making timely adjustments to our mosquito control strategies and measures.  Two different indices, namely, Area Ovitrap Index (AOI) and Monthly Ovitrap Index (MOI), are recorded in our community surveillance programme which covered 38 strategic locations throughout the territory.  AOI indicates the extensiveness of the distribution of Aedine mosquitoes in a surveyed area while the MOI is the average of all AOIs of the same month, which reflects the distribution and activities of Aedes albopictus in the whole territory.


Ovitrap Indices in 2004


8.            The MOIs and AOIs recorded in 2004 are shown in Appendix 1.  It can be seen that the MOIs from January to April were lower than that of 2000-2003 (Appendix 2).  MOI increased sharply from 11.9% in April to 31.6% in May.  Although the rise followed the seasonal pattern observed in the last four years, the MOI in May had already exceeded the average of the past four years (26.8%).  The higher rainfall recorded in March and April might be part of the reason for the sharp rise observed in May.  The index may climb further in the coming warmer months if effective and sustainable interventions are not undertaken.  In April, there were eight areas with AOI over 20% whereas Aberdeen, Kwun Tong Central and Tseung Kwan O had exceeded 40%.  However, in May, only 8 areas had AOI below 20%.  The number of areas with AOI greater than 40% increased from three in April to ten in May.  Five survey areas were found to have AOI over 50% which included Lam Tin (50.0%), Fanling (55.1%), Ma On Shan (51.9%), Tai Wai (61.8%) and Yuen Kong (50.0%). 


Anti-Mosquito Steering Committee


9.            The Anti-Mosquito Steering Committee (AMSC), chaired by the Permanent Secretary for Health, Welfare and Food and comprises of 11 bureaux and departments, was established in 2002 to formulate mosquito control strategy in Hong Kong.  In anticipation of the forthcoming wet season, the AMSC met on 6 May 2004 and endorsed a three-pronged strategy which encompassed intensified preventive and enforcement actions, strengthened surveillance scheme and enhanced publicity programmes, in a bid to contain the risk of mosquito-borne disease, mainly dengue fever, to the community.


10.          On preventive measures, FEHD would activate the district inter-departmental anti-mosquito response mechanism once the Area Ovitrap Index (AOI) reached 20% instead of 30% as in the past.  All relevant departments would conduct intensive on-the-spot inspections to the concerned districts followed by elimination of breeding sources and application of larvicides to potential breeding grounds that are non-removable.  The AOIs of Aberdeen, Kwun Tong Central and Tseung Kwan O, with AOIs exceeding 40% in April, decreased significantly in the month of May as a result of the concerted efforts made by various departments.


11.          On surveillance mechanism, a Port Ovitrap Index (POI) was launched this year to better monitor the mosquito infestation situations in port areas.  A total of 30 port areas, shown in Appendix 3, have been selected for the surveillance and the neighboring areas of every port would also be covered in the program.  POI of seven groups of port areas recorded from January to May is tabulated in Appendix 4. The Port Monthly Ovitrap Index of May was 6.1, with the highest POI of 32.5% detected in cross boundary check points, including Lo Wu, Lok Ma Chau, Man Kam To and Sha Tau Kok.  For areas with high indices, district pest control offices, concerned government departments and other relevant organizations like Airport Authority, Kowloon-Canton Railway Corporation and freight forwarding companies would be asked to conduct special control operations to lower the ovitrap indices.


12.          On the publicity front, the Committee has intensified its promotion effort by producing a new announcement in the public interest (API) on mosquito preventive measures immediately following torrential or prolonged rains, in addition to the existing four TV and radio APIs.


13.          In the face of the sharp upsurge of ovitrap index in May, the AMSC has requested various departments to further intensify their anti-mosquito efforts with special anti-mosquito operations mounted in key areas (including vacant government lands, railway construction sites as well as potential mosquito breeding places at Tai Wai and Ma On Shan area) immediately after the release of the May ovitrap index on 15 June.  At the AMSC meeting on 21 June, all government departments concerned have also undertaken to enhance their anti-mosquito efforts at areas under their respective purviews in the coming months which include �V


(a)              To employ 500 additional contract staff to enhance mosquito control work including conducting thematic operations targetted at village houses, old tenement buildings and passenger and cargo/container terminals/problematic spots;


(b)             To complete the first round of grass cutting and site clearance at about 600 hygiene hot zones in July and to clear 68 hillside illegal cultivation not zones in the coming months;


(c)              To accord priority to anti-mosquito operation at areas with high ovitrap index and to step up inspection frequency to work sites by contractors to twice a week;


(d)             To conduct daily anti-mosquito inspections at all estates, commercial properties and construction sites, and to mobilise 800 staff and cleansing staff to clear mosquito breeding grounds; and


(e)              To mobilise district organisations such as district hygiene squads, area committees, mutual aid committees and owners' corporations and other non-governmental organisations to take part in anti-mosquito operations at hygiene hot zones in 18 districts in the peak months of July and August.


14.          Detailed strengthened anti-mosquito efforts to be taken by various departments are at Appendix 5.


New initiatives


15           Apart from the enhanced anti-mosquito actions mentioned in the above paragraphs, the AMSC has decided to launch two major initiatives to step up the anti-mosquito effort �V


(a)      Establishment of the District Anti-Mosquito Task Force


To strengthen the coordination of anti-mosquito operations of different departments and to encourage community participation in combating mosquito problem, all 18 districts in Hong Kong will set up their own District Anti-Mosquito Task Force under the Home Affairs Department with operation mode modelling after the Team Clean.  Particular emphasis will be placed on problematic areas which may cut across different departments.  Through closer liaison among government departments and more active involvement of members of the public, we hope that anti-mosquito operation could be carried out more effectively and the anti-mosquito message could be disseminated more widely to various sectors of the community.


(b)     Establishment of the Anti-Mosquito Support Scheme


To ensure that sufficient funding is available to carry out anti-mosquito operations, an ��Anti-mosquito Support Scheme��, with an initial fund of $10 million, will be established for the year 2004-05 to support the 18 District Task Forces in launching their anti-mosquito programmes.  When member departments of the Task Force have exhausted all other sources of funding for anti-mosquito operations, they may seek funding support from the Scheme.  The Scheme will also support anti-mosquito operations on those grey areas which take time to ascertain the management authority or the jurisdiction.



Cases of Japanese Encephalitis


16.          In June, there were two cases of Japanese encephalitis (JE), which left one patient dead and the other in critical condition.  JE is a mosquito-borne disease transmitted by the bites of infected mosquitoes. Culex tritaeniorhychus is the principal vector of the disease.  The mosquitoes breed where there is abundant water such as rice paddies, water-logged abandoned fields, marshes and water collections around cultivated fields. Potential breeding grounds are plentiful in vast areas of the New Territories during rainy season, notably in Yuen Long, Sheung Shui and Tuen Mun.   Mosquitoes become infected by feeding on pigs and wild birds infected with the JE virus.  An infected mosquito transmits the virus to humans and animals during biting.  In Hong Kong, JE is a rare disease, with zero to two cases reported each year.


17.          On vector surveillance, the current dengue surveillance programme operated by FEHD does not provide any information on the prevalence and distribution of the JE vector Culex tritaeniorhynchus, since the vector does not share the same habitat as the dengue carrier Aedes albopictus.  Nor is there any index that can provide scientifically sound figures comparing the prevalence of Culex tritaeniorhynchus in different localities.  FEHD has been monitoring the distribution of Culex tritaeniorhynchus for years, and provides necessary information to the public as well as parties concerned.


18.                         On the containment of the spread of the disease, mosquito control is the mainstay of disease control in the current situation.  The Government is studying the feasibility of pig vaccination in local farms against JE.  At this point, territory-wide vaccination of people against the disease is not warranted balancing the risk of contracting it with the potential side effects of the human JE vaccine.  Nonetheless, DH is monitoring the situation closely and making frequent risk assessment in view of the dynamic situation.


19.          Subsequent to the first JE case, Department of Health (DH) has conducted questionnaire survey with over 500 persons in Kau Wah Keng Sun Chuen where the victim lived, and none of them have reported any neurological symptoms of the disease.  The Department also collected 115 blood samples from local residents for serological tests to ascertain JE exposure, and distributed anti-mosquito publicity materials household near the victim��s residence.  FEHD has also stepped up its mosquito control effort in the area.


20.          Since the confirmation of the second JE case, actions have been taken by departments concerned in Palm Springs in Yuen Long where the patient resides, in an attempt to contain the spread of the disease.  The Yuen Long District Office has carried out grass cutting and desilting works in the vicinity of Palm Springs.  FEHD has also applied larvicides in potential mosquito breeding grounds in the area, including nearby abandoned fields and dense vegetations. Publicity materials were distributed and health talks arranged for nearby residents. In addition, inspections to nearby plantations, private carparks as well as pig farms within 2 km of Palm Springs were conducted.


Community Support


21.          Apart from the efforts made by the Government to tackle the mosquito problem, community involvement is indispensable.  It is important for the public to participate actively in anti-mosquito activities by eliminating potential mosquito breeding grounds in their premises and the neighbourhood.  Members of the public could also use the telephone hotline 2868 0000 or the Housing Department hotline 2712 2712 in reporting mosquito problems.







Health, Welfare and Food Bureau

June 2004