Dengue in Singapore going to be a 'big-time epidemic'

Infection numbers are high and will soar in hot season if virus transmission continues

Singapore is heading for its worst dengue fever epidemic, and the warning comes from Associate Professor Leo Yee Sin, one of the foremost dengue experts here.

Infection numbers for the week ended yesterday will not be out till tomorrow, but they will be a new high for this year as 327 people had already fallen ill by 3pm on Friday.

The previous full-week high was 322 in February.

Prof Leo told The Sunday Times: "We really have to anticipate that we will have a big-time dengue epidemic this year."

"It will be huge," she said. "The question is, how huge?"

The reason she is expecting numbers to soar is that it is unusual for dengue numbers to be so high so early in the year.

About 300 people have been infected each week by the mosquito-borne virus since the epidemic started in January.

Unless transmission of the virus is halted, the number of infections could more than double by the middle of the year, said Prof Leo, who is the clinical director at the Communicable Disease Centre.

This is because in the approaching hotter months, both the virus and mosquito replicate about twice as fast and can spread the disease more rapidly.

Singapore's worst brush with dengue was in 2005, when 14,000 people fell ill and 25 died.

Prof Leo hoped that as doctors are now more experienced in treating dengue patients, there will be fewer or no deaths even though more may fall ill.

She advised those with dengue fever to drink plenty of fluids, preferably isotonic drinks, to stay hydrated. If they lose too much water, they could end up with the more severe dengue shock syndrome and need to be admitted to hospital.

So far this year, more than 3,760 people have been diagnosed with dengue but there have been no deaths. However, the real number of infections may be much higher.

A study of more than 4,000 people in 2004 at a time when dengue cases were rising, found that out of every 23 people infected, only one case was reported, said Prof Leo.

Some people who fall ill might have had mild symptoms or decided to self-medicate.

If that ratio still holds true today, it would mean that more than 80,000 people have actually been infected this year.

Associate Professor Ng Li Cheng, head of the Environmental Health Institute, said the Den-1 virus, which has been on the rise, appears to be a "fit" virus, likely to replicate faster.

A fit virus can make a mosquito ready to spread the disease just three to four days after it bites an infected person, compared to the usual seven days.

The dominant dengue virus for the past six years has been the Den-2. But last month, Den-1 became responsible for more than half the infections.

Although all four dengue viruses are around all the time, when the dominant virus changes, it usually leads to an explosion of infections, since many in the population would have no immunity.

If the National Environment Agency (NEA) can reduce the spread of Den-1, the numbers might not be so high.

An NEA spokesman said expenditure on dengue control this year will exceed last year's $72 million as "efforts will have to be multiplied with the expected surge in cases during the peak season".

It now has 850 officers doing nothing but dengue inspections.

The spokesman added: "We are planning to enhance the team when the situation worsens, but there is a limit to how many more officers we can deploy."

Like Prof Leo, Prof Ng said it is important to bring down the number of infections before the "dengue season" starts next month. Dengue numbers usually peak in the warmer months in the middle of the year.

Dengue infections generally spike every five to seven years, and Dr Ng said Singapore is overdue for such a peak.

Historically, too, each new spike is significantly higher than the last.