Monday, October 03, 2005

If quarantined, dengue patients have less than 20% chance of infecting others

To: Feedback Unit - MCYS
cc: NEA

On Channel News Asia's report of 1 Oct 2005, "Singapore's dengue outbreak has peaked: experts" ( )... "quarantining dengue patients was not recommended by the panel because symptoms appear 24 to 48 hours after infection. It is therefore possible for mosquitoes to bite the person and spread the disease to others during this period." Presumably, such "symptoms" include fever.

However, in the "The Vicious Circle" pictorial of The Straits Times dated 20 Sept 2005 ("No need to quarantine dengue patients"), it was stated that "He (the infected man) can pass the dengue virus to the female Aedes mosquito only during the period when he has fever, which can last from three to seven days". This contradicts with the experts' opinion that transmission can still occur during the first 24 to 48 hours of pre-symptomatic feverless infection period.

Nevertheless, even assuming most dengue patients have an infection period of about 10 days (including the frist 1 to 2 days of the feverless stage), quarantining them upon the onset of fever will still mean the risk of infecting others (through being bitten by the Aedes mosquitoes which then infect others) is reduced by 80 to 90% (taking into consideration that symptoms may not appear for 24 to 48 hours after infection, as the experts are led to believe - I am however curious to know if this has been medically and scientifically proven to be the case as the experts have themselves admitted a lot of their previous assumptions are no longer valid. I am now very sceptical of what is to be believed unless it is medically and scientifically proven recently to be the case - not based on studies done 50 years ago).

Therefore, if it means decreasing the odds of transmission, it may still be worthwhile to consider the option of quarantine to minimize infection.


SINGAPORE : Singapore's dengue outbreak is finally on the decline -- that is the assessment of international experts who are here to review its current anti-dengue measures and to make recommendations. After a record two months of dengue cases, the disease is finally on the decline. This is because the epidemic is coming to the end of its two-month cycle and the peak season is over. The latest outbreak coincided with a global resurgence. But the government's efficiency at controlling the disease probably made the country more vulnerable. Said Dr Paul Reitner, Professor of Entomology at the Pasteur Institute, France, "Singapore really is the outstanding example; throughout the world there is no country in the world that has been so successful in suppressing this virus. So successful, the population born over the last 20 years has a very low herd immunity. In other words many people are susceptible." The panel of local and international experts called for research to guide mosquito control operations. One area that needs studying is where people catch the disease. Said Dr Duane Gubler, director of the Asia-Pacific Institute of Tropical Medicine and Infectious Diseases, "If they are being infected in the home then we need to focus more on finding those mosquitoes. But it's very likely that some of them or many of them are being infected outside of the home." Fogging also needs more research to determine how effective it is in Singapore's urban setting. Said Dr Reiter, "Indoor fogging undoubtedly has an impact, it kills the mosquitoes dead. Outdoor fogging will depend on the obstructions, the air movements so it's really hard to say until you've evaluated." The current search and destroy approach to reduce breeding sites will continue. But with Singapore's low mosquito population, the expert panel recommends using trap and destroy methods as well, such as Ovitraps, which are the perfect size and colour to lure the aedes mosquito. The female mosquito comes in, lays its eggs then flies off again. The eggs are so small they actually slip through a wire mesh into the water below, where they hatch into larvae and eventually turn into mosquitoes. By that time, though, they are too large to escape so are trapped inside. Now the Environmental Health Institute is working on a more advanced model that traps both the mosquito as it lays its eggs, as well as the eggs and the larvae. Quarantining dengue patients was not recommended by the panel because symptoms appear 24 to 48 hours after infection. It is therefore possible for mosquitoes to bite the person and spread the disease to others during this period. The expert panel says public education and community involvement remain the key to controlling dengue, along with efforts by the private sector. Meanwhile, the number of dengue cases dropped slightly between 3pm on Friday and 3pm on Saturday. A total of 74 cases were reported, down from 86 the previous day. This is the third day in a row the numbers have not passed the hundred mark. The weekly total has fallen significantly from 714 cases last week to 541 this week. - CNA /ct


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