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APPENDIX 24
Streptococcus, Group A

DISEASE BURDEN

Epidemiology

For the purposes of the calculations in this report, the committee estimated that there are 4,000,000 new cases of noninvasive Group A Streptococcus (GAS) per year in the United States. These cases were assumed to occur in people 24 years of age and under, with the highest incidence rate in children between the ages of 5 and 14 years. It was assumed that there was no mortality associated with noninvasive GAS disease. It was estimated that there, an additional 15,000 cases of invasive GAS disease and that the incidence rate of approximately 5.7 per 100,000 is the same in all age groups. It was assumed that 10% of invasive GAS disease is fatal. See Table A24–1.

Disease Scenarios

For the purposes of the calculation in this report, the committee assumed that 100% of noninvasive GAS infections result in a limited morbidity lasting 4 days and associated with a health utility index (HUI) of 0.9. The committee estimated that a small percentage of these patients (2,000) develop acute rheumatic fever and experience a more prolonged (28 days) illness associated with an HUI of .54. A very small number of those patients then go on to experience a chronic morbidity associated with an HUI of .82 for the duration of their lifetime.

See Appendix 28 for more information.



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Vaccines for the 21st Century: A Tool for Decisionmaking APPENDIX 24 Streptococcus, Group A DISEASE BURDEN Epidemiology For the purposes of the calculations in this report, the committee estimated that there are 4,000,000 new cases of noninvasive Group A Streptococcus (GAS) per year in the United States. These cases were assumed to occur in people 24 years of age and under, with the highest incidence rate in children between the ages of 5 and 14 years. It was assumed that there was no mortality associated with noninvasive GAS disease. It was estimated that there, an additional 15,000 cases of invasive GAS disease and that the incidence rate of approximately 5.7 per 100,000 is the same in all age groups. It was assumed that 10% of invasive GAS disease is fatal. See Table A24–1. Disease Scenarios For the purposes of the calculation in this report, the committee assumed that 100% of noninvasive GAS infections result in a limited morbidity lasting 4 days and associated with a health utility index (HUI) of 0.9. The committee estimated that a small percentage of these patients (2,000) develop acute rheumatic fever and experience a more prolonged (28 days) illness associated with an HUI of .54. A very small number of those patients then go on to experience a chronic morbidity associated with an HUI of .82 for the duration of their lifetime. See Appendix 28 for more information.

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Vaccines for the 21st Century: A Tool for Decisionmaking Table A24–1 Incidence Rate for Noninvasive and Invasive Group A Streptococcus Infections Age Groups Population Incidence Rates (per 100,000) Cases NONINVASIVE INFECTIONS <1 3,963,000 1,009.34 40,000 1–4 16,219,000 2,466.24 400,000 5–14 38,056,000 8,408.66 3,200,000 15–24 36,263,000 992.75 360,000 25–34 41,670,000 0.00 0 35–44 42,149,000 0.00 0 45–54 30,224,000 0.00 0 55–64 21,241,000 0.00 0 65–74 18,964,000 0.00 0 75–84 11,088,000 0.00 0 85+ 3,598,000 0.00 0 Total 263,435,000 1,518.4 4,000,000 INVASIVE INFECTIONS <1 3,963,000 5.69 226 1–4 16,219,000 5.69 924 5–14 38,056,000 5.69 2,167 15–24 36,263,000 5.69 2,065 25–34 41,670,000 5.69 2,373 35–44 42,149,000 5.69 2,400 45–54 30,224,000 5.69 1,721 55–64 21,241,000 5.69 1,209 65–74 18,964,000 5.69 1,080 75–84 11,088,000 5.69 631 85+ 3,598,000 5.69 205 Total 263,435,000 5.69 15,000 For the purposes of this report, the committee assumed that invasive GAS disease manifests as necrotizing fasciitis (with and without lifetime sequelae) in 10% of cases and toxic shock (lasting 15 days and associated with HUIs of .16 during hospitalization and .58 following hospitalization) for 10% of cases. 80% of the invasive forms of the disease are associated with 2 weeks of illness and HUIs of .62 and .73 for the time spent inpatient and outpatient, respectively. See Table A24–2. COST INCURRED BY DISEASE Table A24–3 summarizes the health care costs incurred by GAS infections. For the purposes of the calculations in this report, it was assumed that all pa-

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Vaccines for the 21st Century: A Tool for Decisionmaking Table A24–2 Disease Scenarios for Group A Streptococcus Infection   No. of Cases % of Cases Committee HUI Values Duration (years) NONINVASIVE   Acute Infection 4,000,000 100.00% 0.90 0.0110 (4 days) pharyngitis, skin infections, etc.   Acute Rheumatic Fever 2,000 0.05% 0.54 0.0767 (28 days) Chronic Rheumatic Fever 100 0.0025% 0.82 25.6422 (discounted quality adjusted life expectancy at onset) INVASIVE   Necrotizing Fasciitis: Severe 1,200 8.00%   ICU   0.16 0.0274 (10 days) Post-ICU   0.45 0.0274 (10 days) Necrotizing Fasciitis: Moderate 300 2.00% 0.51 0.0274 (10 days) Necrotizing Fasciitis: Sequelae 1,050 7.00% 0.61 19.2128 (discounted quality adjusted life expectancy at onset) Toxic Shock 1,500 10.00%   inpatient   0.16 0.0137 (5 days) outpatient following hospitalization   0.58 0.0274 (10 days) Other Invasive Forms 12,000 80.00%   inpatient   0.62 0.0192 (7 days) outpatient after inpatient   0.73 0.0192 (7 days) tients with acute, noninvasive GAS disease seek outpatient medical attention (physician, diagnostics, medication). It was also assumed that all patients experiencing acute rheumatic fever require hospitalization and associated costs. The small number of patients with chronic rheumatic disease require 2 physician visits per year for the duration of their lifetime. For the purposes of this report, it was also assumed that all patients with fasciitis require hospitalization. The costs for severe fasciitis are approximately twice that for moderate fasciitis. Lifelong sequelae associated with necrotizing fasciitis were presumed to occur in most patients and were associated with yearly aftercare costs in approximately half of the patients.

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Vaccines for the 21st Century: A Tool for Decisionmaking Table 24–3 Health Care Costs Associated with Group A Streptococcus Infection   % with Care Cost per Unit Units per Case Form of Treatment Acute Infection   pharyngitis, skin infections, etc 100% $150 1.0 outpatient treatment Acute Rheumatic Fever 100% $3,400 1.0 hospitalization Chronic Rheumatic Fever   duration=life expectancy at onset 100% $50 2.0 physician visit (2/year) Necrotizing fasciitis: severe 100% $7,000 1.0 hospitalization   100% $150 1.0 physician c Necrotizing fasciitis: moderate   hospitalization 100% $3,000 1.0 hospitalization   100% $150 1.0 physician c Necrotizing fasciitis: sequelae 50% $3,000 1.0 aftercare per year Toxic shock   hospitalization 90% $3,000 1.0 hospitalization   10% $15,000 1.0 ventilator support outpatient after hospitalization 100% $250 1.0 physician b plus medication c Other invasive forms   inpatient 100% $4,000 1.0 hospitalization outpatient after inpatient 100% $250 1.0 physician b plus medication c Patients with toxic shock from GAS were presumed to require hospitalization, with 10% requiring ventilator support and more expensive care. All patients with toxic shock were presumed to also require outpatient visits to a specialist and additional medication. Other forms of invasive disease were presumed to be associated with a hospitalization and subsequent outpatient visits to a specialist and additional medication. VACCINE DEVELOPMENT The committee assumed that it will take 15 years until licensure of a GAS vaccine and that $400 million needs to be invested. Table 4–1 summarizes vaccine development assumptions for all vaccines considered in this report.

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Vaccines for the 21st Century: A Tool for Decisionmaking VACCINE PROGRAM CONSIDERATIONS Target Population For the purposes of the calculations in this report, it is assumed that the target population for a GAS vaccine is all infants. It was assumed that 90% of the target population 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. RESULTS If a vaccine program for group A streptococci were implemented today and the vaccine were 100% efficacious and utilized by 100% of the target population, the annualized present value of the QALYs gained would be 16,500. 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 6,200. If a vaccine program for group A streptococci 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 $495 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 $185 million. If a vaccine program for group A streptococci 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 $720 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 $360 million. Using committee assumptions of time and costs until licensure, the fixed cost of vaccine development has been amortized and is $12 million for a group A streptococci vaccine.

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Vaccines for the 21st Century: A Tool for Decisionmaking If a vaccine program were implemented today and the vaccine was 100% efficacious and utilized by 100% of the target population, the annualized present value of the cost per QALY gained is $14,000. 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 $30,000. See Chapters 4 and 5 for details on the methods and assumptions used by the committee for the results reported. READING LIST Bisno AL. Streptococcus Pyogenes. In: Principles and Practice of Infectious Diseases. GL Mandell, JE Bennett, Dolin R eds. New York, NY: Churchill Livingstone, 1995, pp. 1786–1799. Kaplan EL. Group A Streptococcal Infections. In: Textbook of Pediatric Infectious Diseases. RD Feigin and JD Cherry eds. Philadelphia, PA: WB Saunder Company, 1992, pp. 1296–1305.