Which revision of this sentence best creates parallel structure?

To prevent further outbreaks, doctors identified the carriers of the disease and isolating them from the general population.

To prevent further outbreaks, doctors identified the carriers of the disease and isolated them from the general population.

To prevent further outbreaks, doctors identified the carriers of the disease and to isolate them from the general population.

To prevent further outbreaks, doctors identifying the carriers of the disease and isolating them from the general population.

Preventing further outbreaks, doctors identified the carriers of the disease and isolating them from the general population