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Table 2 The weekly outbreak notified cases, estimated total number of transmissions by travelling donors, projected future transmissions and proportion of future transmissions resulting from current infections based on chikungunya outbreak data in Italy 2007 for a 7-day visit [2, 10]

From: Modelling the risk of transfusion transmission from travelling donors

Week number Number of cases Estimated cumulative total number of transmissions (per million) Estimated future transmissionsa (per million) Proportion of yet-to-occur transmissions (%)
n I n \( {N}_v(n)={\displaystyle \sum_{n=1}^{15}}\tau {D}_v\frac{I_n}{N}\varphi \left({D}_i-\frac{1}{2}{D}_v\right) \) \( {N}_{vf}(n)=\frac{\tau \varphi {I}_n\left(6{D}_v\left({D}_i-\frac{1}{2}{D}_v\right)-{D_0}^2\right)}{6N} \) \( \frac{N_{vf}(n)}{N_v(n)} \)
1 1 0.01 0.01 74
2 0 0.01 0.00 0
3 1 0.03 0.01 37
4 1 0.04 0.01 25
5 8 0.14 0.08 54
6 10 0.27 0.10 35
7 26 0.61 0.25 41
8 42 1.16 0.40 35
9 38 1.65 0.37 22
10 48 2.27 0.46 20
11 26 2.61 0.25 10
12 25 2.93 0.24 8.2
13 8 3.04 0.08 2.5
14 9 3.16 0.09 2.7
15 4 3.21 0.04 1.2
  1. aFuture transmissions were calculated using the formula given which estimates the number of transmission after the end of the corresponding week as a result of the observed cases in that week. As the infectious period lasts for 8 days, only 98 % of the future transmissions will actually occur in the week following the observed cases, and 2 % in the week after that. Therefore the number of future transmissions indicated in the table will on average underestimate the true number of future transmission by 2 %