Volume 10, Number 7—July 2004
Research
Model Parameters and Outbreak Control for SARS
, Carlos Castillo-Chavez‡1, Paul W. Fenimore*, Christopher M. Kribs-Zaleta§, Leon Arriola*, and James M. Hyman*Table 1
An extended definition for the transmission rate (β) is the number of persons infected per infectious person per day while the basic reproductive number (R0) is the average number of secondary cases an infectious individual can generate when this rate is introduced into a susceptible population
| Parameter | Definition | Baseline value |
|---|---|---|
| pa | Reduction in risk of infection for class S2 | 0.33 |
| ρa | Initial proportion of the population at higher risk for SARS | 0.77 |
| βb | Transmission rate per day | 0.25 |
| 1/ka | Mean incubation period (days) | 6.37 |
| 1/γ1 | Mean infectious period (days) | 28.4 |
| 1/γ2a | Mean infectious period for persons with diagnosed SARS (days) | 23.5 |
| 1/α | Mean period before diagnosis (days) | 4.85 |
| δa | Induced death rate per day | 0.0279 |
| q | Relative measure of infectiousness for the exposed class | 0.1 |
| lc | Relative infectiousness after isolation has begun | [0,1] |
aBaseline values for k, γ2, α, ρ, p and δ have been taken from reference 3.
bβ = 0.25 is our estimated transmission rate in Hong Kong.
cl = 0 means perfect isolation, while l = 1 means no isolation.
1At the time this work was carried out, Dr. Castillo-Chavez was on sabbatical at Los Alamos National Laboratory and faculty of Cornell University.
2Recall that l = 0 corresponds to complete isolation, whereas l = 1 means no effective isolation occurs. Hence, a decrease in l means an increase in the effective isolation of the infected persons.
