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  Straits Times 4 Sep 07
Most people infected with dengue go undiagnosed
NEA finding means there are many more carriers here than originally thought
By Arti Mulchand

Straits Times 4 Sep 07
Bukit Batok is worst dengue hot spot now
By Tania Tan

Today Online 4 Sep 07
Dengue cluster on verge of a record ... Even as cases fall with temperature drop
Sheralyn Tay

COOLER weather is here and the number of dengue cases has dipped, but this is hardly the time to drop our guard, say officials — and Bukit Batok estate is a case in point. Streets 31, 32 and 34 have become the second-largest dengue cluster ever on record with 73 cases in total, and may even surpass the record set in 2005 at Yishun Street 72, which had 74 cases.

The major culprit of mosquito breeding? Homes, said Mr Tai Ji Choong, head of operations at the National Environment Agency's (NEA) Environmental Health Department.

At the Bukit Batok cluster, Mr Tai said: "We have found 20 cases of breeding in homes … In one pail we found 80 larvae and in a flower vase, we found 60 larvae." Common breeding areas included ornamental containers and dish trays. There were also six breeding sites in public areas, including three drains.

As of yesterday, the number of dengue cases reported last week was 192, compared to 242 in the previous two weeks. But these numbers are still not at a "comfortable level" said Mr Tai, stressing: "We must drive numbers even lower."

This is especially important during lull periods like this one, said Dr Ng Lee Ching, head of the Environmental Health Institute.

"Experts believe that the more you suppress the dengue cases now, during the lull period, then we put ourselves at a better advantage when the warmer months come by," she said.

A low mosquito population means fewer "carriers" of the dengue virus and translates to a lower rate of transmission in the warmer months, she explained.

Suppressing mosquito numbers now is also crucial to ensure that the pool of dengue carriers does not carry over to the next year, avoiding a repeat of the epidemic in 2005, said Dr Ng.

Despite 2004 being a lull year, there were more than 200 cases in December that year. "So when the warm weather came the following July, it soared up to more than 700 cases in September."

The NEA also stressed that while the weather has been cooler of late, this is only relative. "Singapore's weather is conducive to dengue transmission all year round, even during the so-called 'cooler months, so we have to be vigilant all year round," said Dr Ng.

Straits Times 4 Sep 07
Most people infected with dengue go undiagnosed
NEA finding means there are many more carriers here than originally thought
By Arti Mulchand

MOST people who are infected with dengue here are not diagnosed with the disease.

A study of blood samples collected from some 3,500 people living in six dengue hot spots has shown that only one in five victims is diagnosed with the disease. The others either have only mild symptoms, which they brush off as a garden variety fever or cold, or show no symptoms at all, said the National Environment Agency (NEA), which conducted the study.

This is alarming, the agency added, as it means there are many more dengue carriers here than originally thought. Dengue is spread when an Aedes mosquito bites an infected person, and then transfers the virus to other people it bites.

To help combat the problem, doctors in dengue hot spots have been asked to conduct blood tests on patients who show flu-like symptoms. People with symptoms such as fever and rash are also being encouraged to slap on mosquito repellent as a safety precaution.

This year, 6,318 people here have been diagnosed with dengue. However, the study shows this figure is only 'the tip of the iceberg', said Dr Christina Liew, a medical entomologist from the Environmental Health Institute (EHI) - the NEA's research arm - who was involved in the research.

She has a message for anyone feeling unwell: See a doctor, and use mosquito repellent as a pre-emptive measure, so the disease is not spread further.

Dr Ng Lee Ching, head of the EHI, told The Straits Times that the ongoing study, which began in May, showed that half of those who tested positive for dengue showed no symptoms, and did not know they had been infected. Of the rest, more than half had symptoms such as fever or aches, but were not diagnosed as having dengue.

Dr Ng said that getting more people tested for dengue will help increase the reporting rate for the disease and allow the NEA to identify problem areas faster, as well as assess the population's immunity.

The revelation that most of those who have dengue go unnoticed comes just as weekly figures for the disease here dipped below 200 for the first time since mid-May.

Last week, there were 192 dengue cases, the fourth week in a row that the figure has fallen below warning levels.

However, this level is 'not comfortable', and the fight is far from over, said Mr Tai Ji Choong, head of operations of the NEA's Environmental Health Department.

In fact, in some areas, such as Bukit Batok, the situation is still worrying. The cluster around Bukit Batok Street 31, 32 and 34, for instance, could set a new nine-year record - there have been 73 cases there in the last 57 days, and it is still active. The current record was set in 2005, with 74 cases in Yishun Street 72.

And despite the cooler weather - mosquito breeding and activity dip along with the temperature - there are other factors at play, said the EHI's Dr Ng. This year, for example, a new type of dengue - Den 2 - is dominant, so more people are susceptible as they have no immunity to the strain.

She added that cooler weather does not always translate into lower dengue figures. In 2004, for example, figures remained at warning levels through the year-end period, although that is not the traditional dengue season because of the cooler, wetter weather.

And from July to September the following year, even through temperatures fell, the number of cases went up. High year-end figures also have implications for next year's dengue situation: When the warmer weather sets in, the situation will likely get worse.

'The more we suppress the dengue cases now during the lull period, the more we put ourselves at an advantage when the warmer months come,' said Dr Ng.

Straits Times 4 Sep 07
Bukit Batok is worst dengue hot spot now
By Tania Tan

THERE are now 73 dengue cases and counting in Bukit Batok - a whisker shy of the nine-year record of 74 cases at a stretch in a single hot spot.

The record was set in Yishun during the 2005 epidemic. Then, dengue cases climbed to an all-time high since 1989, which was when the authorities adopted the system of clocking cases in hot spots around the island.

Singapore has seen 6,318 dengue cases this year, with figures hitting epidemic levels of over 378 cases per week in July. Though they have dipped recently to about 200 cases weekly, it is too early to celebrate, says the National Environment Agency.

The Aedes aegpyti mosquito which spreads the disease has been biting in Bukit Batok Street 31 and Street 34 for 57 days so far.

Having such a serious problem in one area for almost two months is considered unusual.

The reason however, was all too familiar. Like the rest of the island, mosquitoes breeding in homes was the main cause of infections. Most of the 20 worst cases - where up to several hundred larvae were found in a single container - happened in homes.

Even Hong Kah Town Council, which looks after the area, has been plagued with the problem. It has been fined a total of $1,200 for six cases of mosquitoes breeding outdoors over the last two months, in areas such as carparks and drains.

Mr Ang Mong Seng, an MP for Hong Kah GRC, said that the large area under the council's charge - with 800 blocks in the constituency - made it difficult at first to catch all the breeding spots.

Checks have been stepped up to ensure that history does not repeat itself. 'It's a huge area and checks must be done thoroughly. It's quite laborious,' he said.

Search-and-destroy efforts are performed once a week by a team of 21 trained pest control officers, or twice weekly in the worst spots. Town council staff watch out for potential breeding grounds, while fliers and posters have also made the rounds.

Residents said they were aware of the situation, but were not too worried. 'We'll probably be a bit more careful now,' said 25-year-old physiotherapist Chan Jiahui, who lives within the hot spot area.
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