Table 1 Description of model parameters and their values used in estimating travellers transmission risks for the respective chikungunya [2, 10] and Q fever [1, 3] outbreaks
From: Modelling the risk of transfusion transmission from travelling donors
Symbol | Dimension | Description | Chikungunya | Q fever |
|---|---|---|---|---|
I | - | Number of infections: number of infections in the risk area. | 247 | 837 |
N | - | Population size: the size of the local population in the risk area. | 3,977,508 | 55,725 |
Do = t obs | Time | Duration of the observation: the time from the 1st day of reported cases until the day of the last reported case; or for a series of observations: the time from the start until the end of each observation period. | 105 days (15 weeks) | 1050 days (35 months) |
\( \lambda =\frac{I}{N{D}_0} \) | 1/time | Incidence rate: the rate of infection accrual in the risk area. | 5.9 × 10−7 per day | 1.4 × 10−5 per day |
D i | Time | Duration of infectious period: the time in which a traveller is infectious. | 8 (1–12) days | Acute: 14 (10–17) days Chronic: 12 (3–21) months |
D x | Time | Duration of infectious donation period: the time in which a traveller might give blood transfusion during his infectious period after returning home. | ||
p d | - | Proportion of donors: the proportion of donors among the general population. | 3.53%a | 2.37%a |
τ = p d f v | 1/time | Rate of donors visiting the risk area: this is calculated from a proportion of donors (p d ) among the number of visitors to the risk area per unit time (f v ). | 0.35 donors/daya | 0.24 donors/daya |
\( \varphi =\frac{1}{D_d} \) | 1/time | Donation rate: number of donations per unit time, this depends on the inter-donation interval (D d ), i.e. time in between subsequent donations by donors. | 0.005 per daya (D d = 215) | 0.005 per daya (D d = 215) |
D v | Time | Duration of visit: length of stay of visitors in the risk area. | 7 daysa | 14 daysa |
t | Time | Time: the time since the start of the observation. | ||
t e | Time | Time of donor entry: the time at which a travelling donor arrives in the risk area within the observation period. | ||
t i | Time | Time of infectivity: the time at which the travelling donor is presumed to obtain an infection. | ||
t x | Time | Time of donation: time at which an individual donor is assumed to deliver an infected donation. | ||
N v | - | Number of transmissions - from travelling donors after returning to their home country. | ||
N vf | - | Number of future transmissions – from travelling donors after the end of the so far observed transmission, so after time point t obs . |