More dengue cases cropping up in the west

5% of last year's cases from there - up from less than 1% five years ago
Jessica Jaganathan, Straits Times 9 Jul 08;

FIVE in 100, or 5per cent, of last year's more than 8,800 dengue fever cases were reported from western Singapore.

It is not the island's most dengue-infested zone but scientists have noticed a spike in the number of cases from five years ago, when less than 1 per cent of the country's cases - 0.6 per cent, to be exact - came from there.

A study of the rise in the number of dengue cases in certain areas - done by research scientists from the Environmental Health Institute of the National Environment Agency (NEA) - found a link between these rising numbers and the dengue-spreading Aedes aegypti mosquito population.

In 2003, 1.2 per cent of breeding sites in four areas in West Coast and Clementi were those of the Aedes aegypti. Last year, the figure leapt to nearly half - 48.8 per cent - of breeding sites.

The Aedes aegypti mosquitoes are also gaining a foothold in other newer estates, such as Buona Vista, Bukit Batok, Sengkang and Woodlands. They contributed to a quarter of dengue cases last year, compared to 8per cent in 2003.

The newer areas used to host mainly the Aedes albopictus. While it can also cause dengue, outbreaks are more associated with Aedes aegypti, which typically bites more than one person.

The Aedes aegypti is also an 'urbanised mosquito' which flourishes where there are people and man-made containers that hold water and become perfect breeding sites. The Aedes albopictus, however, fares better in forested areas.

The Aedes aegypti already has a foothold in the central and south-east areas of Singapore.

Dr Ng Lee Ching, who heads the Environmental Health Institute, said: 'The more urbanised the location, the easier it is for the Aedes aegypti to be established.'

Doctors in the island's west told The Straits Times that they are seeing more patients than a few years ago.

Dr Jacqueline Yam, a general practitioner in Jurong East, said the increase has come mainly from those working in the marine, shipping and construction industries, which are close by.

The west has hosted two large dengue clusters this year. Some 127 breeding sites were found in homes there and 120 households were fined.

In the 1970s, the Aedes aegypti was confined to the east. Its eggs - which, when dried, can last for half a year - could have been brought over when people moved homes. Also, because fewer dwellers in the west were exposed to dengue, fewer had immunity.

The NEA has stepped up its efforts to seek out and destroy breeding sites in five areas in the west. The work started earlier in the year as well, before hot weather set in.

A housewife in Jurong West, who wanted to be known only as Madam Wong, 53, now sprays insecticide in her house at least twice a week, after having fallen ill with dengue fever last month.

'I'm very worried that my family will get it, or I'll get bitten again - and I hear it's more serious the second time around,' said the former Hong Konger, who has lived here for 13 years.

There have been 2,761 cases of dengue in the first 25 weeks of the year, fewer than the 3,215 recorded during the same period last year.

But the weekly number of cases has stayed high, with 160 cases last week.

The situation is worst in Toa Payoh Lorong 1, with 42 cases reported.

The NEA urges that there be no let-up in vigilance, since this is the hottest period of the year, when the Aedes aegypti thrives.