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898 cases of dengue reported last week: NEA

The National Environment Agency said on Tuesday (July 8) this was a sharp rise from the 674 cases reported the previous week, and noted that the Aedes mosquito population had doubled since May.

SINGAPORE: The National Environment Agency (NEA) said there was a "sharp rise" in the number of reported cases of dengue in the week ending July 5, and warned that it expects the number of cases to rise further during the ongoing peak dengue season.

In a statement on Tuesday (July 8), NEA said there were 898 reported cases of dengue in the week ending July 5, and the figure was a sharp rise from the 674 reported cases from the previous week. As of July 7, there have been a total of 9,697 reported cases of dengue in 2014. DENV-1, the strain of virus that caused the 2013 epidemic, remains dominant, accounting for almost 90 per cent of infections, according to the NEA.


The agency said that its Gravitrap surveillance system revealed that the population of adult Aedes aegypti mosquitoes has doubled since May 2014.

The NEA said it usually sees a higher transmission of dengue in the country in the hotter months of June to October, due to the accelerated breeding and maturation cycles for the Aedes mosquitoes and shorter incubation periods for the dengue virus.

"NEED TO REDUCE MOSQUITO POPULATION URGENTLY"

The NEA, other Government agencies from the Inter-Agency Dengue Task Force, and all town councils are continuing to check public areas and housing estates for potential breeding grounds, with officers carrying out daily checks for breeding habitats in these areas. More than 1.5 million inspections have been carried out this year, the agency said, with space spraying and Gravitraps used to eliminate adult mosquitoes. 

"We need to reduce the mosquito population urgently," the NEA said.

At the community level, NEA is calling residents to play their part in removing stagnant water, to deprive the mosquitoes of their breeding habitat.

Those infected with dengue should protect themselves from mosquito bites by applying repellent regularly, and those showing symptoms suggestive of dengue should see their GPs early to be diagnosed, the agency said.

As of July 7, there are three hotspots with 172 cases in Flora Drive, 153 cases in Kovan Road and 116 cases in Hougang.

NEA said most of the cases are caused by the same strain of the dengue virus.

There are in total four dengue serotypes, with strains 1 and 2 being the most common in causing outbreaks in Singapore.

Last year's dengue epidemic was caused predominantly by strain 1, and this year, it is accounting for almost 90 per cent of all infections.

Strain 1 was most common during the 2005 dengue outbreak, and so community immunity was built up.

Professor of Infectious Diseases, Annelies Wilder-Smith, from NTU’s Lee Kong Chian School of Medicine, said: “In 2005, we had a major outbreak and with lots of cases of dengue serotype 1. And so that builds up the herd immunity against that particular serotype. So after a while, the cases actually come down.

“But then another serotype can come in at a time when there's less immunity against that particular serotype.

"Since 2007, we've had outbreaks with serotype 2. And then again it builds up a herd immunity, and so we had two lull years in 2011 and 2012.

“Last year, in 2013, we had a major dengue outbreak and it was again due to dengue serotype 1 because by that time, the herd immunity of the population was low enough to allow another outbreak to happen."

Experts estimate about half the population in Singapore has no immunity against dengue type 1.

Professor Leo Yee Sin, senior consultant at Tan Tock Seng Hospital’s Infectious Disease Clinic, said: “We would only be able to build up immunity against dengue type 1 after being infected with dengue type 1.

"At this moment, the community level, the immune level in Singapore is still relatively low, so in other words, we are still at high risk of dengue transmissions in Singapore."

Traditionally, the highest risk groups are children and young adults as immunity increases with age.

But experts said they are seeing a trend in recent years with more older people getting infected.

An international study on dengue vaccines is expected to be out this year-end, but experts said more research needs to be done on its relevance to Singapore. 


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