Table 2.

Incidence rate ratio of ventilator-associated pneumonia for trends and disruption in 2007 in ICU

Characteristics	Intervention group: Interrupted surveillance, unit A		Control group: Continuous surveillance, unit B
	Adjusted IRR of VAP (95% CI)a	P	Adjusted IRR of VAP (95% CI)a	P
Bivariate model
Trend, per quarter	0.98 (0.93 to 1.03)	0.45	1.01 (0.97 to 1.05)	0.69
Period
Before surveillance disruptionb	1.00 (Ref.)		1.00 (Ref.)
After surveillance disruptionc	2.17 (1.05 to 4.47)	0.036	1.37 (0.74 to 2.55)	0.31
Full modeld
Trend, per quarter	0.98 (0.92 to 1.04)	0.43	1.02 (0.97 to 1.06)	0.50
Period
Before surveillance disruptionb	1.00 (Ref.)		1.00 (Ref.)
After surveillance disruptionc	2.31 (1.03 to 5.17)	0.042	1.36 (0.72 to 2.56)	0.35

NOTE: CI, confidence interval; IRR, incidence rate ratio; VAP, ventilator-associated pneumonia. ^aAfter multivariate Poisson regression. ^b Period 1 (2004 to 2006). ^c Period 2 (2007 to 2010). ^d Adjusted for gender, age, patient origin, immunosuppression, diagnosis category, antibiotics and SAPSII at admission in the unit. The two other variables, trend (per quarter) and period (period 1 vs. period 2), were forced in the model.