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
1. Binder P, Attre O, Boutin JP, et al. Medical management of biological warfare and bioterrorism: place of the immunoprevention and the immunotherapy. Comp Immunol Microbiol Infect Dis 2003;26(5-6):401-21.
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.
9. Stephenson J. Monkeypox outbreak a reminder of emerging infections vulnerabilities. JAMA 2003;290(1):23-4.
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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