AFTER seven weeks of rising infection rates, new dengue cases finally dropped last week. A total of 218 people caught the mosquito- borne disease, down from 263 the week before. The number might fall again this week, as there were only 99 more cases between Sunday and 3pm yesterday. The drop in infections follows increased efforts by the National Environment Agency (NEA).
The NEA now has 1,000 officers scouring the country for mosquito breeding sites and destroying them. So far, they have carried out more than two million inspections. The NEA has also taken out advertisements urging people to get rid of stagnant water in their homes. More breeding sites are found in homes than in public areas or construction sites. The danger is not over, as the number of cases for last week remains above the epidemic threshold figure of 191 a week.
However, the number of big clusters, defined as those which have 10 cases or more within 150m of each other, has fallen from seven at the start of the week to four yesterday. The biggest is at Pasir Ris Street 11 where 24 people are ill – a far cry from clusters of more than 40 people just days ago. Large clusters are particularly worrying.
On Sunday, Minister for the Environment and Water Resources Vivian Balakrishnan warned: “If there are enough infected people and mosquitoes in any given area, a critical mass of infection will lead to an exploding chain reaction.” So far, 3,450 people have been diagnosed with dengue this year, with more than 1,000 needing to be hospitalised. Three have died. Singapore is currently in the peak dengue transmission season.
The NEA said warmer weather increases the replication rate of the virus, and hastens the growth of mosquitoes. There are also fears that the dominant virus might change to one that has not been very active in recent years. If this happens, more people will lack immunity against dengue. Once a person has the virus, he is protected against being infected by the same strain again. However, he is not protected against the other three strains.
People who are infected a second or subsequent time are susceptible to getting the far more dangerous dengue haemorrhagic fever. Over the past decade, the predominant virus here has been the Den-2. The sudden switch of predominant viral serotype from Den-2 to Den-1 in 2004 led to the last epidemic in 2005 when more than 14,000 people were infected and 27 died. Historically, dengue epidemics here come in five-year to seven-year cycles with each peak significantly higher than the previous one. So an epidemic is possible this year or next.
Aware of the danger of a switch in the predominant viral type, the NEA successfully rushed to stop the small outbreak of Den-3 in Marsiling last month. Most people in Singapore have no protection against either Den-3 or Den-4.