The Mortality Rate for VAP Depends on Which of the Following

The mortality rate for VAP depends on which of the following?
1) Length of stay on the ventilator
2) Presence of underlying disease
3) Prior antimicrobial therapy
4) Presence of a heated humidifier

A) 1 and 2 only
B) 2 and 3 only
C) 1 and 4 only
D) 1, 2, 3, and 4