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Cholera Cost Model Methods

Costs | Cases | Probabilities | Direct Costs | Indirect Costs | Cost Data | References

Cholera Cost Estimates

Total costs for a specific country 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.

The cholera cases included in the model were those considered severe enough to require medical treatment and, in the absence of treatment, would result in at least 7 days of lost productivity and carry a measurable probability of death.

Cholera cases were allocated to 1 of 5 categories:

  1. Infected with cholera; treated in the formal healthcare system (ie, hospital or clinic) and died
  2. Infected with cholera and treated in a hospital
  3. Infected with cholera and treated in an ambulatory (clinic) setting
  4. Infected with cholera; not treated in the formal healthcare system and died
  5. Infected with cholera; not treated in the formal healthcare system and survived 

Cholera cost model

Cholera Case Counts

According to the World Health Organization (WHO), the number of cholera cases reported globally each year is assumed to be a marked underestimate of the actual number of cases that occur. Cholera is underreported for a number of reasons, including the following:

  • Many individuals infected with cholera are unable to seek or access health care.
  • Cholera is often not differentiated from other diarrheal diseases.
  • Not all diagnosed cases are reported to public health or health ministry officials.
  • Not all countries collect and report cholera incidence publicly.

Since the total economic cost borne by each country depends largely on case incidence, use of official numbers would lead to significant underestimation of total cost. To counter this underreporting, we calculate the number of cholera cases by using incidence numbers estimated and published in the literature.2,3 Specifically, we use the incidence rates for endemic countries from Ali and colleagues (2012) and apply them to 2010 population data.

Cholera Probabilities

Probabilities for treatment, hospitalization, and death vary according to a country’s WHO Epidemiological Region. If a case occurred in a country with reduced access to formal health care, then there was a higher probability of no treatment, hospitalization, and death. Our cholera incidence assumptions were derived from case estimates in Ali et al (2012) with further guidance from Dr. David Sack of Johns Hopkins University.2,3 The remaining probabilities are based on assumptions made by the IDCC authors from the UPMC Center for Health Security.

We assume that the probability of a cholera case being treated is 0.75 or 75% in WHO Epidemiological Regions identified as having high or very high child and adult mortality (designated as “D” or “E” regions) ,0.92 or 92% in “B” or “C” regions and 1.0 or 100% in ”A” regions. Conversely, the probability of no treatment is 1 minus the probability of treatment.

1 – 0.75 (prob. of treatment*) = 0.25 or 25% (prob. of no cholera treatment in ”D” or “E” regions)

1 – 0.92 (prob. of treatment) = 0.08 or 8% (prob. of no cholera treatment in ”A”, “B”, or “C” regions)

*reduced access to formal health care

Of those cases that are treated, we also assumed the case fatality rates (CFR) provided in Ali et al (2012). We allocated 25% of these deaths in the treated arm and 75% of deaths in the non-treated arm. As a result, the probability that a treated cholera case results in death ”floats” conditional on the adopted CFR for that country.

  Table 1: Cholera Case Probabilities for WHO D and E Regions

Cholera Case Event

Probability of Event

Meaning

Treated

0.75

75% of infected cases were treated

  Died

Country-specific

25% of the expected deaths based on the country’s CFR (Ali, et al, 2012)

  Survived

1-P(Diedtreated)

 

    Hospitalized

0.75

75% hospitalized of those that survived

    Ambulatory (clinic)

0.25

25% ambulatory of those that survived

Not treated

0.25

25% of infected cases were not treated

  Died

Country-specific

75% of the expected deaths based on the country’s CFR

  Survived

1-P(Diednot treated)

 

  Table 2: Cholera Case Probabilities for High Resource Countries*

Cholera Case Event

Probability of Event

Meaning

Treated

0.92

92% of infected cases were treated

  Died

Country-specific

25 % of the expected deaths based on the country’s CFR (Ali, et al, 2012)

  Survived

1-P(Diedtreated)

 

    Hospitalized

0.50

50% hospitalized

    Ambulatory (clinic)

0.50

50% ambulatory

Not treated

0.08

8% of infected cases were not treated

  Died

Country-specific

75% of the expected deaths based on the country’s CFR

  Survived

1-P(Diednot treated)

 

 

Cholera Direct Costs

Direct costs are those associated with the provision of health care. We assume that the only direct costs for cholera stem from either outpatient clinic use or hospitalization and, as a result, occur only in the “treated” arm of our case allocation model. We assume a 50% premium above the hospitalization costs to account for the costs of supportive care (eg, antibiotics, intravenous fluids) and diagnostic tests. No premium is applied to clinic care. Prices per clinic visit and hospitalization day are from the WHO-CHOICE data.4

Cases that resulted in hospitalization were assumed to require 3.63 days of inpatient care. Number of clinic visits depends on the degree of case illness and was assumed to be 3 days for treatment in hospital and 2 days for ambulatory (ie, clinic) treatment.4

Table 3: 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-CHOICE4
*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

Incorporating Antimicrobial Usage

Treatment for cholera, in addition to fluid replacement, often includes the provision of antimicrobial therapy. Antimicrobials, while not always used, have the potential to decrease duration of symptoms and hospitalization by approximately 1 day based on a reduction of stool volume.5 In the model, we assume that treated individuals have a 66% chance of receiving antimicrobial therapy, based on our review of the literature and discussions with subject matter experts. Consequently, the amount of productive days lost and hospitalization days are down-weighted to reflect the likelihood of receiving antimicrobials.

Cholera Indirect Costs

Indirect costs are those associated with loss in productivity due to 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 cholera cases in which the person survived. To account for productivity losses from a caregiver, we added an additional 0.5 days of per capita GDP for every day a person was ill.

Lost productivity value = labor days lost to illness × daily per capita GDP of cholera survivors

We assumed a present discounted value approach in estimating the productivity costs due to death. Since cholera mortality occurs disproportionately among children, lost life years were weighted as follows:

life years lost =
(0.8 x [country life expectancy – 15]) + (0.2 x [country life expectancy – 30])

The resulting years lost are then multiplied by annual per capita GDP and discounted at 3%.4, 6-15

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

Cholera Cost Data

Hospital and clinic costs: Prices for healthcare utilization were derived from the WHO’s “Choosing Interventions that Are Cost Effective” (WHO-CHOICE) database. WHO-CHOICE 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.”4 Costs per clinic 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 2008 to 2010 purchasing-power adjusted US dollars using the country-specific inflation rate.4,6-15

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.16 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 Index (WDI) database.17

References

  1. The World Bank. World Development Indicators. http://data.worldbank.org/data-catalog/world-development-indicators. Accessed October 26, 2011.

  2. World Health Organization. Cholera [fact sheet]. August 2011. http://www.who.int/mediacentre/factsheets/fs107/en/. Accessed October 26, 2011.

  3. Sack D. Johns Hopkins Bloomberg School of Public Health. Cholera burden of disease estimates. http://www.jhsph.edu/dept/ih/globalhealthresearch/cholera/index.html. Accessed October 26, 2011.

  4. Ali M, Lopez AL, You YA, et al. The global burden of cholera. Bull World Health Organ 2012; 90:209-218A.

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

  6. Greenough III WB, Gordon RS, Rosenberg IS, et al. Tetracycline in the treatment of cholera. Lancet  1964; 1:355-377.

  7. Kirigia J, Sambo L, Yokouide A, Soumbey-Alley E, Muthuri LK, Kirigia DG. Economic burden of cholera in the WHO African region. BMC Int Health Hum Rights 2009;9:8.

  8. Cook J. Are cholera and typhoid vaccines a good investment for a slum in Kolkata, India? [doctoral dissertation]. University of North Carolina Chapel Hill. 2007.

  9. Jeuland M, Cook J, Poulous C, Clemens J, Whittington D; DOMI Cholera Economics Study Group. Cost-effectiveness of new-generation oral cholera vaccines: a multisite analysis. Value Health 2009;12(6):899-908.

  10. Sridhar S. An affordable cholera vaccine: an important step forward. Lancet 2009;374:1658-1660.

  11. Naficy A, Rao MR, Paquet C, Antona D, Sorkin A, Clemens JD. Treatment and vaccination strategies to control cholera in sub-Saharan refugee settings: a cost-effectiveness analysis. JAMA 1998;279(7):521-525.

  12. Jeuland M, Whittington D. Cost-benefit comparisons of investments in improved water supply and cholera vaccination programs. Vaccine 2009;27(23):3109-3120.

  13. Poulos C, Riewpaiboon A, Stewart JF, et al. Costs of Illness due to endemic cholera. Epidemiol Infect 2011. doi:10.1017/S0950268811000513

  14. Vu DT, Hossain MM, Nguyen DS, et al. Coverage and costs of mass immunization of an oral cholera vaccine in Vietnam. J Health Popul Nutr 2003;21(4):304-308.

  15. Sack DA. When should cholera vaccine be used in cholera-endemic areas? J Health Popul Nutr 2003;21(4):299-303.

  16. Murray J, McFarland DA, Waldman RJ. Cost-effectiveness of oral cholera vaccine in a stable refugee population at risk for epidemic cholera and in a population with endemic cholera. Bull World Health Organ 1998;76(4):343-352.

  17. World Health Organization. Global Health Observatory Data Repository: Cholera Number of Cases. http://apps.who.int/ghodata/?vid=2250. Accessed November 22, 2011.

  18. World Health Organization. World Health Statistics. 2011:80-87. http://www.who.int/whosis/whostat/EN_WHS2011_Full.pdf. Accessed June 14, 2011.

  19. International Monetary Fund. World Economic and Financial Surveys: World Economic Outlook Database. http://www.imf.org/external/pubs/ft/weo/2011/01/weodata/index.aspx. Accessed October 26, 2011.