DENGUE FEVER OUTBREAK IN BUKIT BATOK

DENGUE FEVER OUTBREAK IN BUKIT BATOK:

(Update): 7.

Dr Lim Wee Kiak asked the Minister for the Environment and Water Resources whether he can provide an update on the recent cluster of dengue fever outbreak in Bukit Batok.

The Senior Parliamentary Secretary to the Minister for the Environment and Water Resources (Dr Amy Khor Lean Suan) (for the Minister for the Environment and Water Resources): Sir, the cluster at Bukit Batok Streets 31, 32 and 34 started on 11th July 2007. The number of cases reported each week increased from seven in mid-July to a peak of 14 cases in early September before declining thereafter. The cluster was finally closed on 4th October with a total of 117 cases reported.

The outbreak in Bukit Batok is largely due to breeding of the Aedes Aegypti mosquito in homes. NEA has thus far uncovered 70 incidences of mosquito breeding, with majority (83%) of the breedings found in homes. The house index is the number of homes found breeding for every 100 homes inspected. For the Bukit Batok cluster, the house index is 2.67, which is almost seven times that of the national average of 0.39.

Since July, NEA and the Hong Kah Town Council have been working together in stepping up the mosquito control

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regime to arrest the growth of the Bukit Batok cluster. From early September, NEA deployed 40 officers on a daily basis to search and destroy all possible mosquito breeding habitats within the cluster, compared to 10 officers when the cluster first emerged in July. From mid-September, the daily inspections were further extended to another 36 housing blocks surrounding the 34 blocks in the cluster, in an effort to curb dengue transmission.

The Town Council also tripled its deployment of pest control officers to about 20 to carry out daily search and destroy operations in the outdoor areas, including pump rooms, rooftops and bin centres. Staff from other estates were roped in to help rid the cluster of potential breeding grounds by patching up treeholes with cement, filling up ground depressions with top soil, and even drilling holes in ash tray containers on rubbish bins in common areas to prevent water from collecting.

The Bukit Batok situation improved also because the grassroots worked proactively with NEA and the Town Council to meet the challenge in eradicating dengue in Bukit Batok. Although the Bukit Batok cluster has closed, NEA and the Hong Kah Town Council are not letting their guards down, and are continuing with regular mosquito control efforts in the estate.

The Bukit Batok episode has provided us with some valuable lessons which I would like to share with Members of the House.

First, it is critical that Town Councils take every measure to ensure proper maintenance and effective checks of common areas and structures under their charge, to prevent creating conditions favourable for mosquito breeding. This is especially important for estates with

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ongoing dengue transmission. For example, at Bukit Batok, water ponding was found in pump rooms due to leaky water pipes and poor gradient of the floor. Breeding was also detected in water tanks as a result of damaged mosquito netting. Such lapses can be prevented by putting in place a robust maintenance and inspection regime.

Second, residents and HDB shop owners can play a part by refraining from cluttering common corridors with potted plants and bulky items, or placing items over scupper drain or concrete drain slabs outside their premises. Bad housekeeping not only gives rise to potential breeding habitats but also hampers inspection by NEA and the Town Council. Proper maintenance and cleaning of corridors and drains are also hindered by heavy cluttering in the common areas. While NEA is working with HDB and the Town Councils to improve the situation, I would like to call for the cooperation of all residents too.

Third, residents going away on holidays or intending to be away from home for more than a week should ensure that mosquitoes cannot breed in their homes in their absence. Residents are advised to leave behind a contact number with their neighbours or the neighbourhood police post/centre so that the authorities can contact them, if necessary.

Last but not least, I would like to stress that all stakeholders must continue to work hand in hand to deny mosquitoes of the opportunity to breed. Any lapses by one party will negate the good efforts put in by others. The Aedes Aegypti mosquito is a home breeder and will thrive if we are not vigilant. Further, as more and more conventional indoor breeding sites such as pails and vases are removed, mosquitoes are now breeding in more

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hard-to-reach and unsuspected places such as dish rack trays and water cisterns. Profuse breeding, some with as many as 200 larvae counts, has been observed in these habitats. The list of potential breeding sites is never exhaustive and every one of us has to diligently check all places where water can possibly be collected.

The overall dengue situation in Singapore has improved in the recent weeks, despite the persistence of the Bukit Batok cluster. Nonetheless, the number of weekly cases at just below 200 is still high. There have since been eight reported fatalities. To reiterate, complacency among anyone in the community can easily weaken all the efforts that we have put in to control the dengue problem. We need to stay vigilant, not only in Bukit Batok but also in the other areas of Singapore, and during both outbreak period as well as non-outbreak period. We must also learn from past experiences in order to deny the Aedes mosquito places to breed.

Dr Lim Wee Kiak: Sir, I would like to ask the SPS whether this cluster could be prevented in the first place. Were there measures that we could take to predict the arrival of this particular cluster, for example, the ovitrap project that was mooted a few years back? What has happened to the ovitrap project, and has it been used for such an incident?

Dr Amy Khor Lean Suan: First, I would like to highlight that dengue is endemic and that it can happen anytime, whether it is peak or off-peak dengue season, as well as anywhere as long as we are not vigilant.

In the case of dengue control within housing estates, such as in Bukit Batok, an important measure is the residents playing a part in preventing mosquito breeding in their homes. If all residents are vigilant in removing stagnant water,

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then such a prolonged outbreak could have been prevented. And this is especially critical in the case of the Bukit Batok cluster because the area has not been affected by dengue cluster for many years. So, the immunity of the residents is low, which means that you just need a few mosquitoes to trigger a large outbreak. Home owners' vigilance is therefore critical so as not to negate the efforts of all the other stakeholders, like the Town Council and NEA.

As regards the use of ovitraps, ovitraps were, in fact, used. And because ovitraps were used and we detected breeding via the ovitraps, the NEA actually started the source reduction efforts even prior to the dengue outbreak in that area. Because of that, we detected 46 both indoor and outdoor breedings even prior to cluster surfacing.

Dr Lim Wee Kiak: One last question on the house-to-house visits for all the families there. As we know, typically, even during the MP's house visit itself, only about 50%, or 60% at most, of the owners are at home. So, does the house index take care of those who were present at home and opened their doors and also those who did not even open their doors? How was the house index calculated?

Dr Amy Khor Lean Suan: For the dengue cluster areas, we inspect every home, which means that if the owners are not at home, the officers will go back again. So, for the Bukit Batok cluster, there were four rounds of intensive source reduction exercise. In fact, some of the NEA staff said that they know how many plastic pails this particular home has got and where the pails are. Together with the grassroots as well as the Town Council, we actually did 17 rounds of house visits.