Table 1.

Per-contact influenza infection transmission probabilities within contact groups

Contact Group	Transmission Probability
Household1
Child-to-Child	0.8
Child-to-Adult	0.3
Adult-to-Child	0.3
Adult-to-Adult	0.4
Community2
Pre-schooler	0.000005
School child	0.000005
Adult (ages 19–52)	0.000075
Adult (ages 53+)	0.000055
Daycares/Playgroups2
Daycares	0.028
Playgroups	0.018
Schools2
Elementary schools	0.012
Middle schools	0.011
High schools	0.010
Workgroups	0.010

1. Within households, the probability that a symptomatic child (age 18 years or less) infects a susceptible child is 0.8; that a symptomatic child infects a susceptible adult (at least 19 years old), or that a symptomatic adult infects a susceptible child, is 0.3; that a symptomatic adult infects a susceptible adult is 0.4 [16].

2. Probability that a susceptible person in the age or school group is infected through contact with a symptomatic person in the group.