The Hospital

The Hospital is the fourth chapter of the first campaign, No Mercy. In this level, the Survivors discover that the hospital is overrun and the patients are infected. The Survivors must travel up flights of stairs while fighting off the hordes of Infected. The Survivors find an elevator, the only way up to the roof, where the helicopter pilot will come to rescue them. Calling the elevator will signal a Horde, which the Survivors must hold off as they wait for the elevator. There is a brief time at which the Survivors may rest in the elevator before they exit onto a windy construction area of the hospital. Carefully navigating the treacherous area, the Survivors finally make it to the safehouse and take one step closer to salvation.

Easter egg
In one of the Examining rooms there is an X-ray of a hand with 4 fingers as seen on the cover.

The second part of the level takes place on the 28th floor of the hospital, likely a reference to popular zombie movie 28 Days Later.