Weekly dengue cases so far this year have hit a new high, with 185 cases recorded in the 26 June-2 July period.
The number exceeded the Ministry of Health’s (MOH) warning levels of 146 cases per week for the first time this year.
And if dengue cases increase to 191 per week, it would take the situation to epidemic levels.
The National Environment Agency (NEA) said that last week’s 185 cases were also higher than the average 66 cases a week recorded in May and 108 cases a week recorded in June last year.
The NEA said dengue cases have been creeping up, with the weekly average number of cases increasing from 106 in May to 149 last month. But it said this is still far from the 2005 dengue outbreak situation.
The NEA said these levels are moving averages based largely on the past five years worth of data.
As such, the higher the previous cases recorded, the higher the warning and epidemic level would be.
The NEA said given that dengue cases have been relatively low in the past years since the 2005 outbreak, this year’s warning and epidemic levels are at the lower end.
In 2006, the warning and epidemic levels were higher, at 256 cases per week and 378 per week, respectively, because of the high cases in 2004 and 2005.
The recent spike comes after a rare type of dengue – DEN-3 – hit the Marsiling area, with about 66 cases reported as of last week.
And the NEA said more cases could be expected if there is a change in the predominant serotype, as there would be fewer people with immunity against the non-predominant serotype.
The current predominant serotype is DEN-2, which has been in circulation for four years.
Historically, a change has been observed to occur every three years.
The NEA said those living in Marsiling, Woodlands, Geylang, Joo Chiat, Ang Mo Kio and Hougang (between Avenue 1 and Lorong Ah Soo) need to be especially vigilant, with more cases popping up there.
An expert said anyone hit by dengue a second time will feel the effect faster.
"If one person were to acquire DEN-3 the first time, he would have symptoms very similar to DEN-1 or DEN-2. However, should he get another infection subsequently, be it DEN-3 followed by DEN-2, or DEN-2 followed by DEN-3, you expect the disease to progress much faster. So you would see the platelets falling much faster. And you would see that the blood becomes thicker at a much earlier instance," said Dr Leong Hoe Nam, a specialist in infectious diseases at the Raffles Hospital.