Chapter 2. Smallpox

This chapter describes the assumptions for the smallpox scenario, including:

• The severity categories.
• The arrival pattern of casualties at the hospital(s).
• The length of stay by hospital unit (i.e., ED, ICU, and the floor).
• The path probability within the hospital(s) and the length of stay.
• The overall outcome probabilities (i.e., probability of discharge and probability of death).
• The assumed level of resource consumption per patient per day per hospital unit.

Footnotes in the text of a particular section refer to references at the end of the section. In the absence of specific references, parameter estimates were obtained from general references listed in the Hospital Module section.

2.1 Severity Categories

For the smallpox scenario, all patients arrive at the hospital(s) at the onset of mild, generalized symptoms.

2.2 Casualty Arrival Pattern

Casualties are assumed to present at the hospital(s) when symptoms appear. For this scenario, we assume the hospital receives casualties with the same overall arrival pattern as the greater epidemic. To estimate arrival, we calculated inhalation of smallpox by individuals exposed to the attack. Above a certain minimum exposure, all of these individuals were assumed to develop smallpox and were normally distributed around the average onset time. Each casualty was then assumed to infect three other individuals prior to hospitalization. The resulting time curve, taking into account time to development of symptoms and increasing numbers of those exposed, shows a characteristic first wave followed by a second wave peaking one to two weeks after.

2.3 Length of Stay By Hospital Unit

The assumed average length of stay (in days) of patients the ED, ICU, and the floor (based on references no. 2 and 7 listed at the end of this section) are:

Average LOS by Hospital Unit	Smallpox case
ED	1
Floor, not via ICU	14
Floor, via ICU	7
ICU	7

2.4 Combined Path Probabilities and Lengths of Stay

The table below shows the assumed probabilities of different "paths" through the hospital(s) (based on references no. 2 and 7 listed at the end of this section). The table shows, for example, that a patient presenting with a case of smallpox has a 19 percent chance of being transferred from the ED to the ICU and then dying in the ICU.

Path	Smallpox case
ED → Discharge	0%
ED → Death	0%
ED → Floor → Discharge	54%
ED → Floor → Death	7%
ED → Floor → ICU → Death	6%
ED → Floor → ICU → Floor → Discharge	3%
ED → Floor → ICU → Floor → Death	1%
ED → ICU → Death	19%
ED → ICU → Floor → Discharge	9%
ED → ICU → Floor → Death	2%

The breakdown of length of stay by patient type summed over all paths is:

Average LOS by Patient Outcome	Smallpox case
Survivors	15.29
Fatalities	7.00
Average Combined	12.43

2.5 Overall Outcome Probabilities

Based on these inputs (and reference no. 5 listed at the end of this section), the overall discharge and death probabilities are:

Outcome	Smallpox case
Discharge	66%
Death	34%

2.6 Resources Consumed Per Patient Per Day

The assumed level of resource consumption per patient per day is shown in the table below:

Resource	Units	Category	Subcategory	Lambda1	Onset
					ED	ICU	Floor
Med/Surg Bed	Unit of Use	Capacity	Floor	1	0	0	0
ICU Bed	Unit of Use	Capacity	ICU	1	0	1	0
Operating Room	Unit of Use	Capacity	OR	1	0	0	0
Airborne Isolation Room	Unit of Use	Capacity	Isolation	0.9	0.167	1	1
Intensivists (CCM)	FTE	Staff	CCM	0.7	0.042	0.042	0
Critical care nurses (CCN)	FTE	Staff	CCN	1	0.167	0.33	0
Surgeons	FTE	Staff	Surgeon	0.3	0	0.083	0
Non-intensivists (MD)	FTE	Staff	MD	0.9	0.083	0	0.021
Non-critical care nurses (RN/LPN)	FTE	Staff	RN	1	0	0	0.146
Respiratory Therapists (RT)	FTE	Staff	RT	0.7	0.083	0.083	0
Radiology machines	Machine Time	Lab/Radiology	Radiology	0.3	0.021	0.021	0
Radiologic Technicians	FTE	Staff	Rad Tech	0.3	0.021	0.021	0
Pharmacists (PharmD/RPh)	FTE	Staff	Pharmacist	0.7	0.021	0.083	0.042
Mechanical ventilator	Machine Time	Capacity	Ventilator	0.9	1	1	0
Ventilator equipment	Unit of Use	Equipment	Vent Tubing	0.9	1	1	0
Oxygen (O2)	Unit of Use	Supplies	Oxygen	0.9	1	2	0
Oxygenation monitoring equipment	Machine Time	Equipment	O2 Monitoring	0.9	0.083	1	0
Surgical supplies	Unit of Use	Supplies	Surgical	0.3	0	0.25	0
Radiology supplies	Unit of Use	Supplies	Radiological	0.3	1	1	0
Antibiotcs for Secondary Pneumonia	Assorted	Pharmacy	Antibiotics	1	0	1	0
Antibiotics intravenous infusion set	Unit of Use	Supplies	IV set	1	1	0.5	0.5
Hemodynamic medications	Unit of Use	Pharmacy	Hemodynamic	0.7	1	1	0
Intravenous fluids	Unit of Use	Pharmacy	IVF	0.7	1	1	1
Intravenous infusions set	Unit of Use	Supplies	IV Set	0.7	1	1	1
Laboratory machines	Machine Time	Lab/Radiology	Laboratory	0.7	0.02	0.042	0.021
Laboratory supplies	Unit of Use	Supplies	Laboratory	0.7	0.5	1	0.5
Temperature monitoring equipment	Machine Time	Equipment	Temperature	1	0.083	1	1
Thromboembolism prophylaxis	Unit of Use	Pharmacy	DVT Prophylaxis	1	0	1	0
Urine output monitoring equipment	Unit of Use	Equipment	U/O	1	0	1	0
Universal Precautions PPE	Unit of Use	PPE	Universal	1	1	1	1
Waste Disposal	Unit of Use	Waste Mgmt	Decon Waste	0.3	1	1	1
Enteral feedings (3/day/patient)	Unit of Use	Nutrition	Enteral	1	0	0.5	0
Oral food (3 meals per day per patient)	Unit of Use	Nutrition	Oral	1	0	0.5	1
Sheet change	Unit of Use	Housekeeping	Laundry	1	1	1	1
Patient infection control	FTE	Epidemiology	Infection Control	0.5	0.083	0.083	0.083
Engineering	FTE	Engineering	Facility	0.7	0.042	0.083	0.042
Janitorial/Housekeeping	FTE	Housekeeping	Janitorial	1	0.125	0.125	0.083
Nutrition	FTE	Nutrition	Counseling	0.5	0	0.083	0.083
Psychological support	FTE	Ancillary	Psychologist	0.5	0	0	0.042
Mortuary	FTE	Mortuary	Morgue	0.1	0	0.083	0.042

1. Lambda captures the resource requirement decay rate for a resource. Lambda = 1 implies no decay; the patient requires a constant amount of the resource while s/he is hospitalized. Lambda <1 implies that less of the resource is required each day the patient is hospitalized. Go to section 2.2 for details.

References

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2. Breman JG, Henderson DA. Diagnosis and management of smallpox. N Engl J Med 2002;346(17):1300-8.

3. Ferguson NM, Keeling MJ, Edmunds WJ, et al. Planning for smallpox outbreaks. Nature 2003;425(6959):681-5.

4. Gani R, Leach S. Transmission potential of smallpox in contemporary populations. Nature 2001;414(6865):748-51.

5. Henderson DA, Inglesby TV, Bartlett JG, et al. Smallpox as a biological weapon: medical and public health management. Working Group on Civilian Biodefense. JAMA 1999;281(22):2127-37.

6. Lane JM. Smallpox and smallpox vaccination. N Engl J Med 2002;347(9):691-2.

7. Legrand J, Viboud C, Boelle PY, et al. Modelling responses to a smallpox epidemic taking into account uncertainty. Epidemiol Infect 2004;132(1):19-25.

8. Robinson-Dunn B. The microbiology laboratory’s role in response to bioterrorism. Arch Pathol Lab Med 2002;126(3):291-4.

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10. Yetman RJ, Parks D, Taft E. Management of patients exposed to biologic weapons. J Pediatr Health Care 2002;16(5):256-61.

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