For this analysis we use the two SI distributions observed from investigations of the first 100 pH1N1 cases in South Africa [22] : (1) the SI distribution between primary cases and laboratoryconfirmed secondary cases only (39%, 24%, 14%, 17%, 3% and 3% for day 1 to 6 respectively), and (2) the SI distribution between primary cases and suspected plus laboratory-confirmed secondary cases (30%, 17%, 20%, 23%, 7% and 3% for day 1 to 6 respectively). We consider suspected secondary cases, individuals that developed ILI symptoms within 14 days from the symptom onset of a confirmed index case within the same household.