Occurs when an infected individual passes the infection on to other individuals, who pass it on to still others, increasing the penetration of the infection into the susceptible population.

Propagated spread

Explanation:

Any direct or indirect contact with an infected person can lead to a propagated spread of infection.When we talk about propagated spread there is no single source of infection that can be pointed out but each infected individual serves as a source of infection.Due to several sources, the penetration fo infection increases and thus propagated spread often leads to outbreaks of infection and is difficult to control as there is no single source of spread. 

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