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APPENDIX 10
Histoplasma capsulatum
Histoplasmosis is a common pulmonary mycosis of humans and animals. It is caused by Histoplasma capsulatum, a dimorphic soil fungus that is isolated from soil with high nitrogen concentrations. It has a definite association with the droppings of bat and avian habitats.
Histoplasmosis occurs at highest incidence in central and eastern areas of the United States, in particular the Ohio River Valley and portions of the Mississippi Valley.
DISEASE BURDEN
Epidemiology
For the purposes of the calculations in this report, the committee estimated that there are 500,000 new infections with Histoplasma capsulatum each year in the United States. The incidence rate varies with age; the highest incidence is seen in people between 15 and 34 years of age. H. capsulatum infections are clustered geographically. The committee estimated that half of the infections occur in people born in the region and half occur in migrants into the area. The infections was associated with an average mortality rate of 0.05 per 100,000 (138 deaths per year). See Table A10–1.
See Appendix 28 for more information.
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Table A10–1 Incidence and Mortality Rates for Histoplasma Infection
Age Groups
Population
Incidence Rates (per 100,000)
% Distribution of Cases
<1
3,963,000
79.28
0.0063
1–4
16,219,000
79.28
0.0257
5–14
38,056,000
105.11
0.0800
15–24
36,263,000
348.84
0.2530
25–34
41,670,000
325.17
0.2710
35–44
42,149,000
161.33
0.1360
45–54
30,224,000
163.78
0.0990
55–64
21,241,000
174.19
0.0740
65–74
18,964,000
102.83
0.0390
75–84
11,088,000
54.47
0.0121
85+
3,598,000
54.47
0.0039
Total
263,435,000
189.80
1.000
500,000 cases
Age Groups
Population
Mortality Rates (per 100,000)
% Distribution of Deaths
<1
3,963,000
0.04
0.0114
1–4
16,219,000
0.01
0.0093
5–14
38,056,000
0.01
0.0290
15–24
36,263,000
0.03
0.0918
25–34
41,670,000
0.03
0.0983
35–44
42,149,000
0.08
0.2467
45–54
30,224,000
0.08
0.1796
55–64
21,241,000
0.09
0.1342
65–74
18,964,000
0.10
0.1415
75–84
11,088,000
0.05
0.0438
85+
3,598,000
0.05
0.0142
Total
263,435,000
0.05
1.0000
138 deaths
Disease Scenarios
For the purposes of the calculation in this report, the committee assumed that most infections are asymptomatic. Half of symptomatic infections were presumed to be associated with a mild flu-like illness. Other manifestations include pneumonitis, disseminated disease, and chronic pulmonary disease. Outpatient treatment of pneumonitis was associated with both inpatient and outpatient treatment. Disseminated histoplasma was associated with an acute and severe phase of illness followed by a more moderate but lengthy recovery. Health utility indexes associated with histoplasma disease range from .9 for a mild flu-like illness to .39 for the acute illness associated with disseminated disease. Table A10–2 shows the HUI and duration associated with the disease scenarios used in the calculations for the report.
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COST INCURRED BY DISEASE
Table A10–3 summarizes the health care costs incurred by histoplasma infections. For the purposes of the calculations in this report, it was assumed that all patients with flu-like illness associated with histoplasma infection require outpatient care of a physician and that half receive medications or diagnostics. All patients with pneumonitis were assumed to incur costs associated with specialist visits and diagnostics. Inpatient hospital costs are included for a small fraction of these patients. It was assumed that half of the patients with disseminated disease would require hospitalization. All patients with disseminated disease would require outpatient treatment lasting several months and including 8 visits to a specialist and expensive medication and diagnostic costs. Approximately 40% of patients with chronic pulmonary disease would require hospitalization and all of the patients would require outpatient treatment similar to that estimated for disseminated disease but for 3 times the duration and cost.
VACCINE DEVELOPMENT
The committee assumed that it will take 15 years until licensure of a histoplasma vaccine and that $360 million needs to be invested. Table 4–1 summarizes vaccine development assumptions for all vaccines considered in this report.
VACCINE PROGRAM CONSIDERATIONS
Target Population
For the purposes of the calculations in this report, it is assumed that the target population for this vaccine is all infants in endemic regions (approximately 900,000 annually) and migrants into the area (approximately 1,300,000 annually at an average age of 28.9 per migrant vaccinee). It was assumed that 90% of the infants born in the region and 10% of migrants would utilize the vaccine.
Vaccine Schedule, Efficacy, and Costs
For the purposes of the calculations in this report, it was estimated that this vaccine would cost $50 per dose and that administration costs would be $10 per dose. Default assumptions of a 3-dose series and 75% effectiveness were accepted. Table 4–1 summarizes vaccine program assumptions for all vaccines considered in this report.
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Table A10–2 Disease Scenarios for Histoplasma Infection
No. of Cases
% of Cases
Committee HUI Values
Duration (years)
Total Deaths
138
Total Cases (new symptomatic and asymptomatic infections)
500,000
Asymptomatic
90%
1.00
Flu-like illness
5.0%
0.90
0.0384 (14 days)
Pneumonitis: outpatient only
3.5%
0.78
0.0384 (14 days)
Pneumonitis: w/ inpatient
0.9%
inpatient care
0.67
0.0274 (10 days)
outpatient care
0.78
0.0384 (14 days)
Disseminated histoplasmosis
0.5%
disseminated intravascular coagulation, splenomegaly, hepatomegaly, fever
0.39
0.0192 (7 days)
recovery
0.90
0.2500 (3 months)
Chronic pulmonary
0.1%
symptomatic, untreated
0.90
0.1667 (2 months)
outpatient treatment
0.90
0.7500 (9 months)
RESULTS
If a vaccine program for H. capsulatum were implemented today and the vaccine was 100% efficacious and utilized by 100% of the target population, the annualized present value of the QALYs gained would be 1,200. Using committee assumptions of less-than-ideal efficacy and utilization and including time and monetary costs until a vaccine program is implemented, the annualized present value of the QALYs gained would be 35.
If a vaccine program for H. capsulatum were implemented today and the vaccine was 100% efficacious and utilized by 100% of the target population, the annualized present value of the health care costs saved would be $29.7 million. Using committee assumptions of less-than-ideal efficacy and utilization and including time and monetary costs until a vaccine program is implemented, the annualized present value of the health care costs saved would be $860,000.
If a vaccine program for H. capsulatum were implemented today and the vaccine was 100% efficacious and utilized by 100% of the target population, the annualized present value of the program cost would be $390 million. Using committee assumptions of less-than-ideal efficacy and utilization and including time and monetary costs until a vaccine program is implemented, the annualized present value of the program cost would be $12.7 million.
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Table A10–3 Health Care Costs Associated with Histoplasma Disease
% with Care
Cost per Unit
Units per Case
Form of treatment
Flu-like illness
(single state)
100%
$50
2.0
physician a
50%
$150
1.0
medication b, diagnostic b
Pneumonitis: outpatient only
(single state)
100%
$350
1.0
outpatient treatment 2 physician b, medication b, diagnostic b
Pneumonitis: w/ inpatient
inpatient care
100%
$5,000
1.0
hospitalization
outpatient care
100%
$350
1.0
outpatient treatment (same as above)
Disseminated histoplasmosis
disseminated intravascular coagulation, splenomegaly, hepatomegaly, fever
50%
$5,000
1.0
hospitalization
outpatient only
50%
$1,250
1.0
outpatient—3 months (8 physician b, 3 medicaion c)
recovery
50%
$1,250
1.0
outpatient—3 months
Chronic pulmonary
symptomatic (untreated, initial treatment)
40%
$5,000
1.0
hospitalization
outpatient treatment
100%
$1,250
3.0
outpatient (same as for disseminated disease)
Using committee assumptions of time and costs until licensure, the fixed cost of vaccine development has been amortized and is $10.8 million for a H. capsulatum vaccine.
If a vaccine program were implemented today and the vaccine were 100% efficacious and utilized by 100% of the target population, the annualized present value of the cost per QALY gained is $300,000. Using committee assumptions of less-than-ideal utilization and including time and monetary costs until a vaccine program is implemented, the annualized present value of the cost per QALY gained is $600,000.
See Chapters 4 and 5 for details on the methods and assumptions used by the committee for the results reported.
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READING LIST
Bullock WE. Histoplasma Capsulatum. In: Principles and Practice of Infectious Diseases. GL Mandell, JE Bennett, Dolin R eds. New York, NY: Churchill Livingstone, 1995, pp. 2340–2353.
Byerly E, Deardorff K. National and State Population Estimates: 1990 to 1994, U.S. Bureau of the Census, Current Population Reports, pp. 25–1127, U.S. Government Printing Office, Washington, DC, 1995.
Hansen KA. Geographical Mobility: March 1993 to March 1994, U.S. Bureau of the Census, Current Population Reports, pp. 20–485, U.S. Government Printing Office, Washington, DC, 1995.
Leissa B, Widerman BL. Histoplasmosis. In: Textbook of Pediatric Infectious Diseases. RD Feigin and JD Cherry eds. Philadelphia, PA: WB Saunder Company, 1992, pp. 1952–1964.
Ventura SJ, Martin JA, Mathews TJ, et al. Advance Report of Final Natality Statistics, 1994. Monthly Vital Statistics Report 1996; 44.
Representative terms from entire chapter:
outpatient treatment
