GIVE

Key West and Singapore: Meeting the Challenge of Dengue Control on Two Island Communities

One of the early television quiz shows in the 1950s was "The $64,000 Question." The title became synonymous with the "big question." A $64,000 prize awarded in 1959 is now equivalent to nearly $480,000! Thus the $480,000 question in Florida as we begin the year 2011 is whether dengue transmission will continue in Key West. Recently several concerned Monroe County agencies met in Key West to chart a new and improved dengue control strategy. Led by the Monroe County Health Department (MCHD), the agencies agreed to launch the Keys Action to Break the Cycle of Dengue (ABCD) Campaign to aggressively engage the Key West Community to reduce dengue transmission in Key West. The ABCD Campaign was announced to the public at a public meeting including invited press on Feb. 8, 2011 at the Monroe County Board of County Commissioners in Key West

Previous BuzzWords Columns by this author chided the Key West community and its community leaders for failing to aggressively support an anti-dengue campaign based on active community participation in Aedes aegypti source reduction. In addition, MCHD was urged in these columns to mount an aggressive public campaign with prominently placed posters and community actions that support the local mosquito control program. It is gratifying that the report of the ABCD Campaign indicates that there must be effective public campaign if there is any hope of mitigating future dengue transmission in Key West.

How has Key West fared in controlling dengue transmission by using only the Florida Keys Mosquito Control District (FKMCD) with no active public participation? The efforts of FKMCD have been extensive but without active community participation it is apparent that there is little chance of FKMCD controlling dengue transmission singlehandedly. It is instructive to compare the dengue situation in Key West with another island community that has also experienced recent epidemic dengue transmission, Singapore. The number of dengue cases in Singapore and Key West since 2007 are shown in Figure 1. The initial message from these data is that Singapore has a substantially higher dengue

KWcases
Figure 1. Annual number of dengue cases in Singapore compared to Key West, Florida.

transmission rate than Key West. After all, the annual number of dengue cases in Singapore ranges from 5000-8000, while the highest number of cases in Key West was 65. The Key West dengue cases, as denoted by the arrow, hardly appear on the graph! Casual inspection of the graph might lead some to conclude that dengue in Key West is not a problem. Elsewhere I discussed absolute number vs. using the incidence of dengue cases in assessing the risk of dengue in a community (see Tabachnick, WJ. 2010. Dengue in Key West: The perfect storm. BuzzWords, Newsletter of the Florida Mosquito Control Association 10(5): 6-7). It is essential to consider that Singapore has a population of 4.9 million, while Key West's population is only 20,000.

Figure 2 provides a completely different picture of the situation when expressed as the number of cases per 100,000 population. The Singapore epidemic declined from a high of 180/100,000 in 2007 to ca. 100/100,000 in 2010 and 2011. Key West experienced a far greater dengue transmission rate in 2010 with an incidence of 325/100,000. There is no question that the risk of dengue in Key West was at least 2 times higher than Singapore in 2010 and it is troubling that Singapore's dengue is declining while Key West's is rising!

Consider Key West's incidence compared to other countries with ongoing epidemic dengue. For example, in 2010 Thailand had one of the worst outbreaks in its history with ca. 100,000 dengue cases among 66 million people, an incidence of 62/100,000. A situation report on dengue transmission throughout Southeast Asia (http://www.searo.who.int/LinkFiles/Dengue_Dengue_update_SEA_2010.pdf) shows that Key West's dengue incidence was higher than that reported in 12 Southeast Asia countries during 2010. Only the Maldives had a higher incidence in 2005-2008 and Bhutan's

DCPT
Figure 2. The annual incidence of dengue cases/ 100,000 people in Singapore compared to Key West, Florida

incidence was 409/100,000 in 2004. By comparison, the per capita income in Maldives was among the highest in SE Asia (at US $4,700 in 2007) and the per capita income in Bhutan was US $1,321 in 2006. Key West per capita income in 2000 was $26,316 with a median of $43,021 (all data from Wikipedia). Clearly, the financial situation in Key West does not explain the inability of the community to mount a more effective anti-dengue campaign to bring down the incidence of dengue.

Table 1 compares features between Singapore and Key West that might help to explain the different dengue transmission rates observed on the two islands. However, just considering the relative density of people, land area, number of rainy days, average temperatures, and average rainfall one has to respect the dengue transmission problem that Singapore faces. Despite this, and despite the substantial efforts and resources of the FKMCD, the incidence of dengue transmission has increased in Key West while it has declined in Singapore (Figure 2).

Table 1. Comparison of selected features of Key West and Singapore that likely influence Aedes aegypti abundance and dengue transmission
  Key West Singapore
Population 20,000 4,900,000
No. of Islands 1 63
Land Size (sq. mi.) 5.9 271.8
Annual Avg. Rainy Days 106 177
Monthly Range 4.7-16 11-19
Total Annual Rain (inches) 38.94 92.25
Monthly Range 1.5-5.5 6-11
Avg. Annual High Temp (°F) 82.9 87.9
Monthly Range (°F) 75-90 86-88
Avg. Annual Low Temp(°F) 73.2 75.4
Monthly Range (°F) 41-68 74-76

Perhaps there are lessons to be learned in Singapore's approach to dengue control. Singapore has an extensive integrated anti-dengue campaign whose key feature is an aggressive and sustained attack against Aedes aegypti. This is a coordinated campaign under the direction of the Singapore National Environment Agency (NEA). One can access the details of Singapore's campaign by going directly to the NEA website at:
http://www.dengue.gov.sg and a summary can be found at:
http://www.straitstimes.com/STI/STIMEDIA/pdf/20101216/
denguesurveillance.pdf

A few points about the Singapore anti-dengue program deserve attention by the health professionals charged with reducing the risk of dengue transmission in Key West. 1) NEA provides an integrated anti-dengue program using mosquito surveillance and control, enforcement, community outreach, public education, and research. 2) Source reduction of Aedes aegypti larval sites is key to a successful program. 3) Dedicated teams, led by one of more than 500 trained NEA officers, inspect 100% of the vacant premises, shops, houses, estates, places of worship, bus interchanges, railroad and bus stations, and schools in three month cycles. 4) Source reduction continues as part of Intensive Source Reduction Exercises (ISREs) ahead of peak periods of dengue transmission. 5) Geographic Information System methods are used to integrate Aedes aegypti monitoring with the location of known dengue cases. 6) Epidemiological investigations are conducted by trained NEA officers to pinpoint possible sources responsible for clusters of dengue cases. 7) NEA has an Inter-Agency Dengue Task Force composed of 26 public, private, and professional organizations designed to strengthen the coordination of dengue control among various agencies. 8) All Singapore Town Councils (TC) managing public housing projects have dedicated mosquito control programs working closely with NEA. TCs having mosquito breeding on the areas they manage are subjected to penalties to encourage continuation of an aggressive mosquito control program. 9) NEA conducts immediate search and destroy operations at affected locations and within the immediate neighborhood. NEA will send an outbreak control team to thoroughly comb any area reporting two or more dengue cases within 150 meters and within 14 days of onset. The outbreak control team will check the area, conduct vector control including fogging if mosquitoes are present, and will continue control efforts until transmission ceases within the targeted zone. 10) Community mosquito control participation is crucial. Aggressive public education through posters, advertisements in newspapers, radio, and TV heighten public awareness. Demographics are used to target educational campaigns to specific groups including school children, parents, homeowners, foreign workers, and travelers. 11) NEA works closely with community grass roots volunteer organizations seeking resident's cooperation by checking for mosquito breeding in their homes and on their property. 12) NEA uses legislation contained in the Control of Vectors and Pesticides Act to enforce the law that prevents people from continually allowing breeding mosquitoes on their property. Owners of residential premises found with mosquito habitats or mosquito breeding are fined $200 for the first offense and an additional $200 for all subsequent offenses. Repeat offenders are brought to court. Owners of non-residential premises can be fined $200 with greater fines for construction sites including a stop work order until the site is cleaned. In 2010, Singapore maintained a 24/7 hotline for people to call to report mosquito breeding or mosquito activity! 13) NEA supports an extensive research program to improve its capabilities against dengue and to enhance Aedes aegypti control in Singapore.

Despite the extensive and laudable effort of the FKMCD against Aedes aegypti in Key West, the total 2009 and 2010 dengue control programs in Key West were below the lofty standards set in Singapore. Certainly the Key West efforts of 2009 and 2010 should not be considered a maximal effort to reduce dengue transmission on the island. It is not entirely fair to compare FKMCD to Singapore, as FKMCD continued to address the Monroe County pest mosquitoes that are its normal targets while also fighting Ae. aegypti. I especially urge the Key West community leaders and public health officials to consider the anti-dengue program showcased in Singapore. The Community Leaders need to take the best parts of the Singapore program and adapt them for use in South Florida. The MCHD meeting in Key West and the start of the ABCD Campaign is a positive and long overdue sign of progress. Now that agencies have stated that they take dengue seriously and plan to join in, the fight no longer rests solely on the shoulders of FKMCD.

Dengue transmission in Key West has been a moment of truth for everyone charged with protecting the public health in Key West, Monroe County, Florida and the U. S. It is a test of our capabilities and resolve. We can and must do better.

wjtWalter J. Tabachnick, Ph.D.
Florida Medical Entomology Laboratory
Professor, Department of Entomology and Nematology
University of Florida, IFAS, Vero Beach, FL