War against dengue ramped up in Singapore

Signs pointing to an imminent epidemic, say experts
Salma Khalik Straits Times 12 Jul 11;

SINGAPORE is going all out to prevent a dengue epidemic that could send hundreds of people to hospital.

The National Environment Agency (NEA) is sending out 1,000 officers daily to scour the island for possible mosquito breeding sites and to destroy them.

In spite of the heightened efforts, three people have already died of dengue so far this year, and about 800 hospitalised. Of the three who died, one had other medical problems. The other two were healthy adults in their 40s.

Last week, the number of new cases surged past the epidemic level, with 211 people infected. This is the highest weekly number in more than two years.

The good news is the numbers are still a far cry from the more than 700 infections a week during the peak of the last dengue epidemic in 2005. That year, 14,209 people fell ill, and 25 died.

Dengue is spread by the Aedes mosquito biting an infected person and passing the virus to other people it bites. Symptoms include a high fever, often coupled with a severe headache, rash, joint and muscle ache, and in some cases, pain behind the eyes and mild bleeding of the nose and gums.

Experts point to several factors that make an epidemic - which is when a disease spreads rapidly in the population - imminent.

One is that dengue epidemics come in five- to seven-year cycles, and it is now six years since the last epidemic in 2005. The recent rise in infections is a hint that things could get worse.

Another is that during the current warm season, mosquitoes mature faster, and the dengue virus replicates at a more frenetic rate.

Yet another reason is the predominant circulating strain of a dengue virus usually changes every three years - but this is the fourth year with the current Den-2 strain.

A switch to any of the other three dengue strains could trigger an epidemic, as people who have had dengue over the past four years are protected against only Den-2. This was why the NEA rushed to stop the small outbreak of Den-3 in Marsiling last month. Most people here have no protection against this strain.

Associate Professor Leo Yee Sin, who heads the Department of Infectious Diseases at Tan Tock Seng Hospital, noted that people who get dengue a second or third time have a higher risk of getting the more dangerous dengue hemorrhagic fever.

According to the Health Ministry, there has been 10 cases of hemorrhagic fever this year.

Lastly, due to the low rate of dengue in recent years compared to some decades ago or to neighbouring countries, Singapore's population lacks immunity and will be more susceptible to any outbreak.

The NEA explained that it now takes far fewer mosquitoes to start an outbreak. The spokesman said its teams are not just going to areas where dengue has surfaced, but also to estates which are clear of the disease to prevent it from taking root.

More breeding spots have been found in homes than in public areas or construction sites. Common sites for mosquito breeding are flower-pot holders, vases, bamboo-pole holders, unused pails and basins. All it takes is a teaspoonful of water for mosquitoes to breed.

The biggest dengue cluster now is at Jalan Kelichap and nearby Upper Paya Lebar Road, where 28 people are down with the disease. There was a new cluster of 10 cases yesterday at Paya Lebar Crescent and Lorong Ah Soo. Other active areas include Woodlands, Geylang, Joo Chiat, Ang Mo Kio and Hougang.

Prof Leo said the disease is more severe in the very young and very old.

'A higher proportion of younger patients develop dengue hemorrhagic fever, and we have more elderly die of dengue infection,' she said.

Patients with dengue tend to stay an average of four days in hospital, she added. And with most public hospitals facing a bed crunch, an epidemic could cause a severe bed shortage.