The burden of dengue infection

April 28, 2007

Scott B. Halstead, Jose A Suaya, Donald S Shepard

The Lancet 2007; 369(9571):1410-1411

Using a prospective population-based cohort of 2,119 school-age children in a rural area of Thailand, Katie Anderson and colleagues [1] provide, in today’s Lancet, important insights into the burden—both economic and human--imposed by dengue infections. Quantification of these burdens is crucial to the formulation by governments, donors, and industry of decisions for the prevention and management of dengue, especially concerning the potential introduction of dengue vaccines or other technologies.

Anderson and co-workers studied the children for 5 years, allowing them to identify a ten-fold variation in dengue incidence and hospitalization rates from year to year that an earlier study, [2] which ran for only 1 year, would not have detected. A further strength of Anderson and colleagues’ study is their intensive surveillance of both mild and severe disease. Usually, notification of suspected dengue cases to public health authorities depends on passive surveillance of hospitalized cases. Although legally mandated in most dengue endemic countries where dengue is endemic, notification is rarely enforced [3]. Because most ambulatory cases of dengue and some hospitalized cases are generally not officially notified, under-reporting is usually the most important challenge to obtaining reliable national estimates of dengue diseases. On the basis of studies like Anderson’s, expansion factors can be derived to adjust for this under-reporting.

Of the 328 symptomatic confirmed dengue infections in Anderson and colleagues’ study, 52 (16%) were classified as dengue haemorrhagic fever on the basis of WHO criteria. Hence, for each case of dengue haemorrhagic fever, there were about five cases of dengue. Additionally, for each of the 96 hospitalized cases (44 cases of dengue fever and 52 of dengue haemorrhagic fever), there were three ambulatory cases of dengue. Therefore, the number of dengue cases (both dengue fever and dengue haemorrhagic fever) was about six times the number of hospitalized cases of dengue haemorrhagic fever or, more informatively, four times the number of hospitalized cases of dengue. If these expansion factors are representative of the experience of symptomatic dengue infection experience in a homogeneous population such as that of Thailand, estimates of the burden of illness for the entire nation can be calculated from hospitalized cases reported to national authorities.

Globally, illness expression in dengue can vary enormously. Factors that affect disease severity include ethnicity, age, nutritional status, the exact sequence of two different dengue infections, the genotype of infecting virus and, of course, the competence of the clinical and laboratory surveillance systems [4]. To document and study this variability, studies similar to that of Anderson and colleagues should be repeated in several other regions.

Anderson and colleagues provided estimates of the dengue burden measured in terms of disability-adjusted life-years (DALYs). On the basis of work by Gubler & Meltzer [5] and as other researchers have done [5-6], the study assumed that dengue carried a disability weight of 0.81, limited to the duration of fever and inpatient care. Individuals with dengue, especially adults, may not recover completely after the fever disappears, continuing to experience discomfort and interference with normal sleep, with school or work patterns, or even experience alterations in emotional wellbeing. By contrast, Lopez and colleagues [7] estimated that the disability weight was only about a quarter of that used by Anderson and co-workers. Further research, including interviews with affected families, would be useful to refine this variable, especially for children. Accepting these caveats, Anderson’s study emphasises the high burden of disease imposed by non-hospitalized cases, with such cases comprising 56% of the total DALYs imposed by dengue, reaching a maximum in 1 year of 73%.

Mainly on the basis of assumptions, Anderson and colleagues also estimated key components of the economic effect of a dengue episode on households, showing that the cost could be substantial. With a broader design and more comprehensive data, future studies could include costs borne by government (eg, provision of health services), employers (eg, paid sick leave for parents), households (eg, loss of non-work time by adults), and society as a whole (eg, economic loss from school absenteeism). Had these other components been included, both the absolute cost associated with dengue as well as its relative magnitude compared with other acute febrile illnesses would have been dramatically greater.

Authors’ affiliations: Pediatric Dengue Vaccine Initiative, Rockville, MD 20852, USA (SBH); and Heller School for Social Policy and Management, Brandeis University, Waltham, Massachusetts, USA (DSS, JAS). halsteads@erols.com. We declare that we have no conflict of interest.

References

  1. Anderson KB, Chunsuttiwat, Nisalak A, et al. Burden of symptomatic dengue infection in children in Thailand: a prospective study. Lancet 2007; 369:1452-59.
  2. Clark DV, Mammen MP Jr, Nisalak A, Puthimethee V, Endy TP. Economic impact of dengue fever/dengue hemorrhagic fever in Thailand at the family and population levels. Am J Trop Med Hyg. 2005;72:786-91.
  3. Zaidi AKM, Awasthi S, DeSilva HJ. Burden of infectious diseases in South Asia. BMJ. 2004; 328:811-15.
  4. Halstead SB. Epidemiology of dengue and dengue hemorrhagic fever. In: Gubler DJ, Kuno GK, eds. Dengue and dengue hemorrhagic fever. New York: CAB International; 1997: 23-44.
  5. Gubler DJ, Meltzer M. Impact of dengue/dengue hemorrhagic fever on the developing world. Adv Virus Res. 1999;53:35-70.
  6. Shepard DS, Suaya JA, Halstead SB, et al. Cost-effectiveness of a pediatric dengue vaccine. Vaccine. 2004;22:1275-80.
  7. Lopez AD, Mathers CD, Ezzati M, Jamison DT, Murray CJL. Global burden of disease and risk factors: New York Oxford University Press and World Bank; 2006.

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