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Dengue Burden of Disease: Time for a change?
Posted by mbeatty on 26 Oct 2009 at 03:04 GMT
Mark E. Beatty,1 Martin I. Meltzer,2 Philippe Beutels3
1 Pediatric Dengue Vaccine Initiative, International Vaccine Institute, Seoul, Republic of Korea;
2 Centers for Disease Control and Prevention, Atlanta, Georgia, USA;
3 Centre for Health Economics Research and Modeling Infectious Diseases, Centre for the Evaluation of Vaccination, Vaccine & Infectious Disease Institute, University of Antwerp, Antwerp, Belgium.
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We read with interest the article by Moran et al.1 regarding the distribution of funding for infectious disease but take exception to the statement “while dengue had a disease burden 20 times lower than helminth infections at 600,000 DALYs in 2004 [it] received nearly twice as much funding.”
Originally introduced by the World Health Organization (WHO) in the 1990’s, DALYs were intended to allow comparison of disease burden among diseases and injuries.2 There are three essential inputs for the calculation: total cases, disability score, and duration of illness. Ignoring under reporting due to difficulties with dengue diagnostics and clinical diagnosis,3 we believe the 600,000 DALYs per year cited by Moran et al. was a conservative estimate because the disability scores used were much lower than generally accepted in the published literature for dengue.4-6
The cited source of the disease burden data of Moran et al., WHO Global Burden of Disease 2004 Update, assigned dengue fever (DF) a disability score of 0.2 and duration of 5.5 days and dengue hemorrhagic fever (DHF) was assigned disability score of 0.5 for 11 days. In the same report an uncomplicated febrile episode of malaria was assigned a disability score of 0.47.7
We recently completed a systematic review of the dengue health economic literature and noted that seven of the eight publications by non-WHO researchers on the disease burden of dengue used a disability score of 0.81 or higher for DF and DHF (Beatty, unpublished communication). Increasing the disability score will increase DALYs estimates. The disability score for an uncomplicated febrile episode of malaria was increased from 0.2 in the 1994 WHO GBD, to 0.47 in the 2004 update, in effect doubling the disease burden. Likewise, others have argued for changes in disability score of dengue-related illnesses.8
Meltzer et al. were the first to use a score of 0.81 for DHF in 1998.4 Because DHF patients require hospitalization and can not care for themselves, Meltzer et al. used a 0.81 disability score (equivalent diseases which interfere with one’s ability to care for oneself) giving a DALY estimate of 658 DALYs/million population. Meltzer et al. used shorter durations of illness but the same disability score for DF because even non-hospitalized DF patients are incapacitated.4 Lum et al. conducted daily quantitative assessments of disability in laboratory-confirmed cases dengue patients that support the assumption of Meltzer et al.9 Patients were asked to rate the limitation of the routine daily activities, which were categorized into health domains or activities with a common objective (e.g. self care, mobility, cognition), due to their illness. They found quality of life was impaired for 9 days among non-hospitalized patients and 13 days for hospitalized patients; of eight health domains evaluated, an average of 5.0 were impaired among non-hospitalized patients, and 6.2 among hospitalized patients.9 Increasing the disability score accordingly could increase the global estimates by 3- to 4-fold.
It should also be noted that DALY calculations do not describe the total impact of disease. As a disease of outbreak potential, dengue causes significant stress to families in endemic regions causing them to sell assets and incur debt to cover the catastrophic medical costs associated hospitalization.11,12 Politicians in endemic countries are also acutely aware of the concerns of their constituencies.13 An assessment of the total burden of dengue should include these kinds of issues in addition to DALY estimates.
In conclusion, Moran et al. provide an important perspective on this issue but also reminds us that numbers are only a starting point for discussions of distribution of infectious disease funding.
1. Moran M, Guzman J, Ropars AL, et al. Neglected disease research and development: how much are we really spending? PLoS Med. 2009; 6: 2:e30.
2.Murray CJ, Lopez AD. Quantifying disability: data, methods and results. Bull World Health Organ 1994; 72: 3: 481–94.
3. Deen JL, Harris E, Wills B, et al. The WHO dengue classification and case definitions: time for a reassessment. Lancet 2006; 368: 9530: 170–3.
4. Meltzer MI, Rigau-Pérez JG, Clark GG, Reiter P, Gubler DJ. Using disability-adjusted life years to assess the economic impact of dengue in Puerto Rico: 1984–1994. Am J Trop Med Hyg 1998; 59: 2: 265–71.
5. Anderson KB, Chunsuttiwat S, Nisalak A, et al. Burden of symptomatic dengue infection in children at primary school in Thailand: a prospective study. Lancet 2007; 369: 9571: 1452–9.
6. Luz PM, Grinsztejn B, Galvani AP. Disability adjusted life years lost to dengue in Brazil. Trop Med Int Health. 2009;14: 2:237–46.
7. World Health Organization. The Global Burden of Disease: 2004 Update, 2008. Available: www.who.int/healthinfo/gl.... Accessed 20 April 2009.
8. King CH, Dickman K, Tisch DJ. Reassessment of the cost of chronic helmintic infection: a meta-analysis of disability-related outcomes in endemic schistosomiasis. Lancet 2005; 365: 9470:1561–9.
9. Lum LCS, Suaya JA, Lian HT, Sah BK, Shepard DS. Quality of life of dengue patients. Am J Trop Med Hyg 2008; 78: 862–7.
10. Halstead SB. Pathogenesis of dengue: challenges to molecular biology. Science 1988; 239: 4839: 476–81.
11. Harving ML, Rönsholt FF. The economic impact of dengue hemorrhagic fever on family level in Southern Vietnam. Dan Med Bull 2007; 54: 2: 170–2.
12. Khun S, Manderson L. Health seeking and access to care for children with suspected dengue in Cambodia: an ethnographic study. BMC Public Health 2007; 7: 262.
13. DeRoeck D, Deen J, Clemens JD. Policymakers' views on dengue fever/dengue haemorrhagic fever and the need for dengue vaccines in four Southeast Asian countries. Vaccine 2003; 22: 1: 121–9.