Yet, as various studies have pointed out, such interventions do not guarantee that an epidemic will not occur. At the same time, while many types of larval control campaigns have been carried out in a variety of locales, there is little reliable information about what such campaigns cost, and to what degree, if any, the resources expended will have a positive effect on the final result. The possibility of a lack of "success" in health interventions can be particularly unsettling for local authorities faced with the decision of whether or not to carry out larval control efforts.
However, new dengue-control guidelines, described in a scientific-journal article, hold the potential to remove some of the guesswork from this process by enabling decisionmakers to more accurately assess the cost-effectiveness of larval control measures. On the one hand, the methods employed provide data regarding the costs of carrying out a rapid-response, emergency intervention and the expected reduction in the number of reported dengue cases. At the same time, the guidelines provide insight into the value of having an early warning system that yields information on a possible outbreak of dengue--even when that system is not 100% accurate.
The guidelines are described in an English-language article in the July 2003 issue of the "Revista Panamericana de Salud Pública/Pan American Journal of Public Health," a scientific and technical periodical published by the Pan American Health Organization (PAHO). The research was conducted by K. John McConnell of the Oregon Health & Science University's Department of Emergency Medicine and Duane J. Gubler of the Division of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, of the Centers for Disease Control and Prevention (CDC).
In developing the guidelines, the researchers chose Puerto Rico as the case study site and, using data on dengue transmission and its likely impacts there, were able to simulate a distribution of economic impacts based on disease rates and economic variables, including the costs of treating patients and the opportunity costs represented by lost wages. "The advantage of using such a mathematical model in this analysis," note the authors, "is that it allows us to ask a number of 'what if' questions without observing their actual implementation in a real-world setting." Drs. McConnell and Gubler used their model to examine a number of different larval-source-reduction scenarios and their associated cost-effectiveness, thereby capturing the range of costs associated with dengue and with larval control programs.
The study also examined how the existence of an early warning system can extend the range of interventions that are cost-effective and are thereby more acceptable to public officials. The authors note: "When no early-warning information is available, a larval control program that costs more than US$ 6.00 per person is not recommended [in the case study in Puerto Rico]. However, with a predicted outbreak, the same campaign is advisable, as long as the intervention can reduce disease rates by 70% or more. More costly programs may be justifiable if they have higher rates of disease reduction."
The researchers caution that "this study does not advocate for emergency vector control in preference to long-term, community-owned programs for larval control." Instead, they say, the guidelines are intended to provide two key insights regarding larval control and its use in avoiding dengue epidemics.
First, larval control measures do not need to be 100% effective, or even 90% effective, in order to be cost-saving. The evidence in Puerto Rico suggests that a number of larval control programs emphasizing the emptying, cleaning, treating, and removal of containers and other sites where eggs are laid are likely to result in overall savings for the community.
Second, the study's findings are meant to "provide incentives for the incorporation of types of early warning systems, which may have substantial benefits even if they are not always 100% accurate." In particular, systems that provide some indication of an increased likelihood of higher levels of dengue transmission may warrant more intensive larval control efforts. Thus, improved surveillance of dengue transmission may lead to economic benefits in areas where this surveillance can be used to predict epidemic-level dengue transmission.
The article can be viewed for free in the PAHO Online Bookstore Web site, at http://publications.paho.org. Additional information on dengue fever is available from the CDC Web site, at http://www.cdc.gov.
The "Revista Panamericana de Salud Pública/Pan American Journal of Public Health" is the main scientific and technical periodical published by PAHO and features research conducted in the Region of the Americas. PAHO, which also serves as the Regional Office for the Americas of the World Health Organization, was established in 1902. PAHO Member States include all 35 countries in the Americas. Puerto Rico is an Associate Member. France, the Kingdom of the Netherlands, and the United Kingdom of Great Britain and Northern Ireland are Participating States, and Portugal and Spain are Observer States.