Figure 2.

Illustration of reference methods used to estimate source subjects and dates of infections. The mean incubation period is 1.5 days. The maximum infectivity is obtained 3 days from infection. (A) Data used by each method consists in dates of onset and end of symptoms for any subject (rectangles). (B) The ‘naive’ method M1 assigned a sequence of transmissions identical to the sequence of cases. Dates of infection are chosen equal to the mean of two consecutive dates. (C) Method 2 integrates as additional constraint the fact that subject i cannot transmit infection during the latent period (equal to the incubation time in this example, 1.5 days). (D) Method 3 takes into account the period between infection and the maximum infectivity of subject (3 days from infection) in addition to the previous method.