Starting from July 2018, there are a total of 57 locations selected for the vector surveillance. Two different indices, namely Area Ovitrap Index for Aedes albopictus (AOI), and Monthly Ovitrap Index for Aedes albopictus (MOI), would be enumerated. AOI indicates the extensiveness of the distribution of Aedine mosquitoes in that particular area surveyed while the MOI is the average of all AOIs within the same month, which reflects the territory-wide situation of Aedes albopictus.

Survey of Aedes albopictus has been carrying out in Hong Kong International Airport since 1998. Starting from 2004, dengue vector surveillance work would be extended to other port areas. Two different indices, namely Port Ovitrap Index for Aedes albopictus (POI), and Port Monthly Ovitrap Index for Aedes albopictus (PMOI), would be enumerated. POI indicates the extensiveness of the distribution of Aedine mosquitoes in particular group of surveyed port areas while the PMOI is the average of all POIs within the same month, which reflects the overall situation of Aedes albopictus in port areas.

The Ovitrap Index for Aedes albopictus can be classified into 4 levels. Specific preventive and control measures will be initiated accordingly. Management of housing estates, hospitals, schools, construction sites and other venues or properties are also advised to take specific measures to contain mosquito problems in their own properties. The 4 levels of Ovitrap Index for Aedes albopictus and actions to be taken by the management are listed in the following table.

Classification Ovitrap Index for Aedes albopictus Action to be taken
Level 1 O.I. < 5%
  • Closely monitor the hygienic condition to prevent breeding of mosquitoes;
  • Conduct weekly inspection to identify breeding / potential breeding places and eliminate such places as far as possible.
  • Public are advised to check and eliminate any possible breeding places within their premises at a frequency not less than once a week (Please go to Advice to Public for details)
Level 2 5% ≤ O.I. < 20%
Level 3 20% ≤ O.I. < 40%
  • To conduct special operations in addition to the regular weekly program to eliminate all breeding / potential breeding places;
  • Private pest control contractor might be employed to control the mosquito problem. Other control measures by using larvicides or adulticides might be feasible.
Level 4 O.I. ≥ 40%

During the survey period, the ovitraps are collected on a weekly basis. At the end of the first week of surveillance, all the ovitraps are retrieved and another batch of ovitraps is set at the same location for surveillance for the second week. The ovitraps retrieved are immediately checked for the presence of larvae or eggs of Aedes albopictus (“Aedes-positive”) for the purpose of compiling the Ovitrap Index (First Phase Ovitrap Index). They are kept in the laboratory for incubation for a week to allow the undetected eggs to hatch into larvae. The hatched larvae are examined to confirm if they are Aedes albopictus. 

At the end of the second week of surveillance, all the ovitraps are retrieved and instantly checked for the presence of larvae or eggs of Aedes albopictus (“Aedes-positive”). The ovitraps retrieved after the first week of surveillance are re-examined to confirm the total number of the Aedes-positive ovitraps (including those in which larvae have hatched at the laboratory). The Ovitrap Index (Second Phase Ovitrap Index) is obtained by combining these two sets of data. The ovitraps retrieved after the second week of surveillance are sent to the laboratory for incubation for one week to allow the undetected eggs to hatch into larvae. The hatched larvae are examined to confirm if they are Aedes albopictus

When the ovitraps retrieved after the second week of surveillance have been kept in the laboratory for incubation for one week, they are re-examined to confirm the total number of the Aedes-positive ovitraps. Finally, the verified data of the two weeks of surveillance will be combined to obtain the final Ovitrap Index (Area Ovitrap Index). 

Ovitrap Index for Aedes albopictus = Number of the Aedes-positive ovitraps/Total number of ovitraps retrieved from a particular area ´ 100% 

The Department has all along adopted the current survey method to detect the presence of Aedes albopictus and will notify the District Environmental Hygiene Offices and the relevant departments of the Ovitrap Indices of various phases once the figures are available, so that they can promptly carry out targeted mosquito prevention and control work. To facilitate the public's access to the latest survey data on the ovitraps for Aedes albopictus, the Department has announced the phased Ovitrap Index for Aedes albopictus for each of the surveyed areas on our webpage since September 2018. Corresponding mosquito prevention and control measures can be taken by the public in a more expeditious manner so as to prevent the spread of dengue fever. 

The Ovitrap Index for Aedes albopictus of each surveyed area is released in three phases. Figures released in the first and second phases are phased indices and the third phase index represents the Area Ovitrap Index of the surveyed area in that month.


The phased Ovitrap Indices for Aedes albopictus for 57 locations in October 2019 are provided below:

Hong Kong
District Surveyed area First Phase Ovitrap Index Second Phase Ovitrap Index Area Ovitrap Index
Central/Western Central and Admiralty 0.0%
Sheung Wan & Sai Ying Pun
(Formerly: Central, Sheung Wan & Sai Ying Pun)
5.0%
Sai Wan 0.0%
Eastern Chai Wan West 0.0% 0.0%
Shau Kei Wan & Sai Wan Ho 0.0% 0.0%
North Point 12.5% 7.3%
Southern Aberdeen and Ap Lei Chau 1.9% 2.8%
Pokfulam 1.8% 0.0%
Deep Water Bay & Repulse Bay 0.0% 1.9%
Wan Chai Tin Hau 0.0% 1.9%
Wan Chai North 1.9% 0.9%
Happy Valley 0.0%
Islands
Islands Cheung Chau
Tung Chung

Kowloon
District Surveyed area First Phase Ovitrap Index Second Phase Ovitrap Index Area Ovitrap Index
Yau Tsim Tsim Sha Tsui 1.6%
Tsim Sha Tsui East 1.9% 0.9%
Mong Kok Mong Kok 1.8%
Sham Shui Po Cheung Sha Wan
Lai Chi Kok
Sham Shui Po East
Kowloon City Ho Man Tin 11.1%
Kowloon City North
Hung Hom 0.0%
Lok Fu West 0.0%
Kai Tak North 0.0%
Wong Tai Sin Wong Tai Sin Central 1.5%
Diamond Hill 1.7% 0.9%
Ngau Chi Wan 5.6%
Kwun Tong Kwun Tong Central
Lam Tin
Yau Tong 0.0%
Kowloon Bay

New Territories
District Surveyed area First Phase Ovitrap Index Second Phase Ovitrap Index Area Ovitrap Index
Sai Kung Tseung Kwan O South (Formerly: Tseung Kwan O)
Tseung Kwan O North
Sai Kung Town
Sha Tin Tai Wai 4.8% 5.6%
Sha Tin East (Formerly: Yuen Chau Kok) 1.7% 0.8%
Ma On Shan 9.4% 9.5%
Sha Tin Town Centre and Fo Tan (Formerly: Wo Che) 2.0% 2.9%
Tai Po Tai Po 0.0%
North Fanling 0.0%
Sheung Shui 1.8%
Yuen Long Tin Shui Wai 0.0%
Yuen Kong 0.0%
Yuen Long Town 0.0%
Tuen Mun Tuen Mun North 1.6%
Tuen Mun South 1.9%
Tuen Mun West 6.3% 3.1%
So Kwun Wat 1.8% 0.9%
Tseun Wan Tsuen Wan Town 0.0%
Tseun Wan West 2.0%
Ma Wan 0.0%
Sheung Kwai Chung
Kwai Tsing Kwai Chung
Lai King
Tsing Yi South (Formerly: Tsing Yi)
Tsing Yi North

The following graph makes a comparison of the average of the Monthly Ovitrap Index for Aedes albopictus from 2009 to 2018 and the Monthly Ovitrap Index for Aedes albopictus for 2019:

Monthly Ovitrap Index

Please click here for a graph of the Ovitrap Index for Aedes albopictus from 2009 to 2018.

Please click here for the average of the Monthly Ovitrap Index for Aedes albopictus from 2009 to 2018.

Please click here for the average of the Port Monthly Ovitrap Index for Aedes albopictus from 2009 to 2018.

Please click here for the Area Ovitrap Index for Aedes albopictus of all surveyed areas from January to December 2019.

The Monthly Ovitrap Index for Aedes albopictus for September 2019 is 6.5%.

The Port Monthly Ovitrap Index for Aedes albopictus for September 2019 is 1.2%.