Table 5. Time Series Models for Staphylococcus aureus 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 | 2.71 | 2.19 | ||
| Post-intervention | 1.78 | 1.98 | ||
| Percent change | −34.31% | −9.37% | ||
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| Time Series Modelb | Beta [95% CI] | p | Beta [95% CI] | P |
| Intervention | −0.87[−1.25, −0.49] | 0.000 | 1.58 [−1.31, 4.47] | 0.273 |
| Adjusted S areus colonization pressure |
11.35 [6.86, 15.84] | 0.000 | 11.17 [6.39, 15.95] | 0.000 |
| AR(1) | −0.40 [−0.77, −0.04] | 0.032 | ||
| AR(2) | −0.36 [−0.73, 0.01] | 0.059 | ||
| MA(1) | −0.21 [−0.46, 0.03] | 0.083 | ||
| MA(5) | −0.33 [−0.57, −0.09] | 0.008 | ||
| MA(6) | −0.44 [−0.70, −0.18] | 0.001 | ||
| MA(7) | −0.91 [−0.99, −0.83] | 0.000 | ||
| Constant | −1.37 [−3.04, 0.31] | 0.107 | −3.63 [−7.40, 0.14] | 0.059 |
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| Model parameters | ||||
| Adjusted R2 | 0.35 | 0.46 | ||
| Durbin-Watson statistic | 2.09 | 1.87 | ||
| Q(4) p-value | 0.14 | 0.22 | ||
| Q(8) p-value | 0.66 | 0.18 | ||
| Q(12) p-value | 0.71 | 0.28 | ||
Note: AR(1)= auto-regressive variable, 1; AR(2)= auto-regressive variable, 2; MA(1)= moving-average variable, 1; MA(5)= moving-average variable, 5; MA(6)= moving-average variable, 6; MA(7)= moving-average variable, 7. 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.