Table 3. Comparison of Methicillin-resistant Staphylococcus aureus (MRSA) Infection Rates in the Intervention Intensive Care Unit (ICU) (2002-2007) and Control ICU (2005-2007).
| Intervention (Surgical) ICUa | Control (Medical) ICU | |||
|---|---|---|---|---|
| Crude Rates | Rate (per 1,000 ICU-days) | Rate (per 1,000 ICU-days) | ||
| Pre-intervention | 1.96 | 2.19 | ||
| Post-intervention | 1.15 | 1.05 | ||
| Percent change | −41.37% | −51.95% | ||
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| Time Series Modelb | Beta [95% CI] | p | Beta [95% CI] | p |
| Intervention | −0.90 [−1.40, −0.40] | 0.001 | −1.51 [−4.01, 1.00] | 0.228 |
| Adjusted MRSA colonization pressure |
10.78 [5.41, 16.15] | 0.000 | 1.37 [−1.76,4.51] | 0.377 |
| AR(1) | -- | -- | −0.57 [−0.91, −0.24] | 0.002 |
| AR(2) | -- | -- | −0.38 [−0.69, −0.07] | 0.018 |
| MA(5) | −0.36 [−0.62, −0.11] | 0.005 | -- | -- |
| MA(9) | −0.30 [−0.53, −0.08] | 0.009 | -- | -- |
| MA(10) | −0.31 [−0.57, −0.06] | 0.017 | -- | -- |
| MA(12) | -- | -- | −0.93 [−1.00, −0.86] | 0.000 |
| Constant | −0.13 [−1.33, 1.06] | 0.822 | 2.32 [−0.18,4.82] | 0.068 |
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| Model parameters | ||||
| Adjusted R2 | 0.42 | 0.70 | ||
| Durbin-Watson statistic | 2.12 | 2.37 | ||
| Q(4) p-value | 0.24 | 0.28 | ||
| Q(8) p-value | 0.66 | 0.54 | ||
| Q(12) p-value | 0.90 | 0.40 | ||
Note: AR(1)= auto-regressive variable, 1; AR(2)= auto-regressive variable, 2; MA(5) = moving average variable, 5; MA(9) = moving-average variable, 9; MA(10) = moving-average variable, 10; MA(12) = moving-average variable, 12.
The inclusion of AR and MA terms in the model addressed serial correlation seen, as evidenced by the Durbin-Watson statistic and the Box-Ljung Q(k) tests of the unadjusted model.
a
Models are based on all available data for the surgical ICU (61months, 2002-2007) and medical ICU (24 months, 2005-2007).
b
In the multivariate time series model, ‘beta’ indicates the magnitude and the direction of the variable in the model, while the p value and 95% CI indicate the precision and significance of the variable within the model.