# Dengue Cost Model Methods

## Dengue Cost Estimates

Total costs for individual countries were calculated by adding the direct and indirect costs associated with case incidence. Costs are reported in purchasing power parity (PPP) adjusted 2010 US dollars.

Dengue cases were allocated to 1 of 4 categories:

1. Infected with dengue fever (DF) and treated in an ambulatory (clinic) setting
2. Infected with DF and treated in a hospital
3. Infected with severe dengue fever (SDF) and treated in a hospital
4. Infected with SDF and died

## Dengue Case Counts

The number of dengue cases reported globally each year has been found to be a marked underestimate of the actual number of symptomatic dengue cases that occur.1 Dengue is underreported for a number of reasons, including the following:

• Many individuals with classic dengue fever do not present for care.
• Dengue fever is a flulike illness and can be difficult to diagnose.
• Not all diagnosed cases are reported to public health or health ministry officials.
• Not all countries collect and report dengue incidence publicly.

Since the total economic cost borne by each country depends largely on case incidence, the use of official numbers would lead to significant underestimation of total cost. To counter the effects of underreporting, we adopt the methods used by Shepard and colleagues (2011) by assuming a multiplier that expands the official numbers of case counts.3 In some countries, there are sophisticated surveillance studies that inform the value of the multiplier. In countries that lack surveillance data, we assume a case multiplier of 15.3 The map provides both the reported cases for dengue and the multiplier-adjusted number used to estimate disease costs.

A number of other countries are assumed to have endemic dengue but provide no official case number estimates; for them, we apply a method previously documented in the literature and assume a 1% incidence for symptomatic cases. Specific nations in northern Africa are assigned a case count of zero, and, based on evidence from published studies, the African nations that are assumed to have cases are assigned a higher probability of DF than countries in the rest of the world.4

## Dengue Probabilities

The probability of being allocated to 1 of the 4 groups depends on assumptions made by the IDCC authors. For example, based on published literature, we assume a 94% probability that a symptomatic case is dengue fever (DF), except in Africa, where the probability of DF is 98.8%. Conversely, we assume the probability that a symptomatic case is severe dengue fever (SDF) is 1 minus the probability of DF, or 6% (1.2% in Africa).

1 – 0.94 (probability that symptomatic case is DF) =
0.06 (probability that symptomatic case is SDF)

Of symptomatic cases that are assumed to have DF, we assume, based on the literature, that 90% are treated in an ambulatory setting. As a result, the probability that a symptomatic case is a DF patient treated in a clinic (outside of Africa) is 0.94 multiplied by 0.90, or .846 (ie, 0.94 x 0.90 = 84.6%).5

##### Table 1: Dengue Case Probabilities
 Dengue Case Event Probability of Event Meaning Asymptomatic 0.76 76% of infected cases are asymptomatic Symptomatic 0.24 24% of infected cases are symptomatic Dengue Fever (DF) 0.94 or 0.988 94% of symptomatic cases are DF outside of Africa, and 98.8% of symptomatic cases are DF in Africa Ambulatory 0.90 90% of DF cases are ambulatory Hospitalized 0.10 10% of DF cases are hospitalized Severe Dengue Fever (SDF) 0.06 or 0.012 6% of symptomatic cases are severe dengue outside of Africa, and 1.2% in Africa Hospitalized 0.987 98.7% of SDF cases are hospitalized Dead 0.013 1.3% of SDF cases die

## Dengue Direct Costs

Direct costs are those associated with the provision of health care. We assume that the only direct costs for dengue stem from either outpatient clinic use or hospitalization. Since the care required for DF and SDF is largely supportive, we do not explicitly model treatment costs, such as medication. Instead, we assume a 50% premium above the hospitalization costs to account for the costs of supportive care (ie, intravenous fluids) and diagnostic tests. No premium is applied to clinic care. Prices per clinic visit and hospital day are derived from the WHO-CHOICE data.6

Days in the hospital were set at 3.8 and 12 for DF and SDF, respectively. The number of clinic visits depends on severity of illness; assigned values are 4.2 days for ambulatory DF cases, 4.6 days for hospitalized DF cases, and 6 days for hospitalized SDF cases.6,7

##### Table 2: Direct Medical Costs in 2010 PPP-Adjusted \$US
 WHO Subregion* Inpatient Cost Clinic Cost African Region AFR D \$71.24 \$12.52 AFR E \$29.22 \$5.73 Region of the Americas AMR A \$665.45 \$65.50 AMR B \$162.96 \$22.83 AMR D \$50.68 \$9.66 Eastern Mediterranean Region EMR B \$432.45 \$45.41 EMR D \$28.84 \$6.70 European Region EUR A \$502.65 \$51.21 EUR B \$95.17 \$14.92 EUR C \$184.37 \$24.69 South-East Asian Region SEAR B \$46.64 \$9.27 SEAR D \$26.82 \$6.04 Western Pacific Region WPR A \$660.59 \$65.35 WPR B \$72.57 \$12.37

Source: WHO-CHOICE6

*Subregions are divided into mortality strata:
A = very low mortality for children and adults
B = low mortality for children and adults
C = low mortality for children, high mortality for adults
D = high mortality for children and adults
E = very high mortality for children and adults

## Dengue Indirect Costs

Indirect costs are those associated with the loss in productivity from illness and death. The value of lost productivity due to illness is assumed to be labor days lost to illness multiplied by the daily per capita gross domestic product (GDP) for DF and SDF cases that survived.

lost productivity value =
labor days lost to illness × daily per capita GDP of DF and SDF survivors

To account for productivity losses from a caregiver, we added an additional 0.5 days of per capita GDP for every day of illness causing a person to be away from work or school.

We adopted a standard accounting approach in estimating the productivity costs due to death: country life expectancy minus 20 years. The resulting years lost are then multiplied by annual per capita GDP and discounted at 3%.8-12

value of lost productivity due to death =
(life years lost × annual per capita GDP) / (1.03life years lost

## Dengue Cost Data

Hospital and Clinic Costs: Prices for healthcare utilization were derived from the WHO-CHOICE database, in which hospital costs are the estimated cost per stay and represent “the hotel component of hospital costs, ie, excluding drugs and diagnostic tests and including other costs such as personnel, capital, and food costs.” Costs per clinic visit are similar in that they account for everything except for drugs and diagnostic tests. Prices are specific to the 14 Global Burden of Disease (GBD) regions. Each price was adjusted from 2005 to 2010 purchasing-power adjusted US dollars using the country-specific inflation rate.6,8-12

Case Data: Dengue case reports for 2010 were derived from a number of different sources but primarily from WHO regional disease situation reports. The Pan American Health Organization (PAHO), the WHO Western Pacific Region, the WHO Regional Office for South-East Asia, and the WHO for Europe all reported dengue case numbers for 2010.12-16 These reported data have been incorporated into the cost model. Dengue incidence was not reported in 2010 by the WHO Africa and Eastern Mediterranean Regions; however, these regions are known to have endemic dengue.17,18

Population, Per Capita GDP, and Life Expectancy: Population and per capita GDP data were downloaded from the International Monetary Fund’s World Economic Outlook (WEO) database.19 To keep units consistent, we use the per capita GDP expressed in purchasing-power adjusted US dollars. Life expectancy data were downloaded from the World Bank’s World Development Indicators (WDI) database.20

## References

1. Dengue and dengue haemorrhagic fever [fact sheet]. World Health Organization website. March 2009. http://www.who.int/mediacentre/factsheets/fs117/en/. Accessed October 26, 2011.

2. Dengue: the fastest growing mosquito-borne disease in the world. World Health Organization website. October 29, 2010. http://www.who.int/neglected_diseases/integrated_media/
integrated_media_2010_Dengue_vs_malaria/en/index.html.
Accessed October 26, 2011.

3. Shepard D, Coudeville L, Halasa Y, Zambrano B, Davan GH. Economic impact of dengue illness in the Americas. Am J Trop Med Hyg 2011;84:200-207.

4. Halstead SB, Streit TG, Lafontant JG, et al. Haiti: absence of dengue hemorrhagic fever despite hyperendemic transmission. Am J Trop Med Hyg 2001;65:180-183.

5. Shepard DS, Suaya JA, Halstead SB, et al. Cost-effectiveness of a pediatric dengue vaccine. Vaccine 2004;22:1275-1280.

6. CHOosing Interventions that are Cost Effective (WHO-CHOICE). World Health Organization website.  2008. http://www.who.int/choice/country/country_specific/en/index.html. Accessed March 12, 2013.

7. Beatty ME, Beutels P, Meltzer M, et al. Health economics of dengue: a systematic literature review and expert panel’s assessment. Am J Trop Med Hyg 2011;84(3):473-488.

8. Luz PM, Grinsztejn B, Galvani AP. Disability adjusted life years lost to dengue in Brazil. Trop Med Int Health 2009;14(2):237-246.

9. Beaute J, Vong S. Cost and disease burden of dengue in Cambodia. BMC Public Health 2010;10:521.

10. Huy R, Wichmann O, Beatty M, et al. Cost of dengue and other febrile illnesses to households in rural Cambodia: a prospective community-based case-control study. BMC Public Health 2009;9:155.

11. Canyon DV. Historical analysis of the economic cost of dengue in Australia. J Vector Borne Dis 2008;45(3);245-248.

12. Suaya JA, Shepard DS, Siqueira JB, et al. Cost of dengue cases in eight countries in the Americas and Asia: a prospective study. Am J Trop Med Hyg 2009;80(5):846-855.

13. Number of reported cases of dengue and dengue hemorrhagic fever (DHF) in the Americas, by country: figures for 2010 (to week noted by each country). Pan American Health Organization website. Updated May 20, 2011. http://new.paho.org/hq/dmdocuments/2011/dengue_cases_2010_May_20.pdf. Accessed November 21, 2011.

14. Number of reported cases of dengue fever and dengue hemorrhagic fever (DF/DHF) in the Western Pacific Region, by country: figures for 2010 (to week noted by each country). World Health Organization Western Pacific Region website. http://www.wpro.who.int/emerging_diseases/Dengue_WPRO_2010_8Sep2011.pdf. Accessed November 21, 2011.

15. Centralized information system for infectious diseases. Query 6041, dengue, number of cases. World Health Organization Regional Office for Europe website. Undated.http://data.euro.who.int/cisid/?TabID=267589. Accessed November 21, 2011.

16. World Health Organization Regional Office for South-East Asia. Mapping of neglected tropical diseases in the South-East Asia region. Communicable Disease Newsletter 2011;8(1). http://203.90.70.117/PDS_DOCS/B4702.pdf. Accessed November 22, 2011.

17. Sang RC. Dengue in Africa. [review article] TropIKA.net November 27, 2007. http://www.tropika.net/svc/review/061001-Dengue_in_Africa. Accessed June 14, 2011.

18. Chinnock P. Dengue fever: is it now Africa’s turn to experience major epidemics? TropIKA.net November 12, 2009. http://www.tropika.net/svc/news/20091112/Chinnock-20091114-News-Dengue-Africa. Accessed June 14, 2011.

19. World economic and financial surveys: world economic outlook database. International Monetary Fund website. June 17, 2011. http://www.imf.org/external/pubs/ft/weo/2011/01/weodata/index.aspx. Accessed October 26, 2011.

20. World development indicators. The World Bank website. Update December 21, 2012. http://data.worldbank.org/data-catalog/world-development-indicators. Accessed March 29, 2013.