842 infection control & hospital epidemiology july 2017, vol. 38, no. 7
(teaching vs nonteaching), surveillance year, and 4-week period. Poisson confidence intervals were used. Facilities were defined as “teaching” if they were associated with medical training and research programs and as “nonteaching” otherwise. Segmented Poisson regression
analysis.To evaluate
the
effectiveness of the Québec MRSA guidelines on HA-MRSA incidence rates, we performed a segmented Poisson regression to examine the change in incidence rates for CLABSI and HA- MRSA for 3 distinct periods (Table 1). Models were built using data from facilities that participated in each surveillance program from 2006 to 2015. SPIN-SARM surveillance began in 2006, and themodel’s first interval coincided with the pre-MRSA guideline period (January 1, 2006, to March 31, 2007),withMarch 31, 2007 as the first break point. The next time segment, interval 2 (April 1, 2007, to January 2, 2010) represented the period immediately after the INSPQ MRSA guideline was published. Although INSPQ guidelines were published in June 2006, an 11-month window in the pre-guideline interval was reserved to account for distribution, training, and implementation periods. Interval 2 also encompassed the MHSS “Action Plan on the Prevention and Control of Nosocomial Infections” for 2006–2009 as well as the evaluation of guideline implementation.14 The second break point, January 3, 2010,marked the beginning of interval 3, which encompassed the period after MRSA guidelines were published (January 3, 2010, to March 31, 2015) and corresponded to the timeframe outlined in the MHSS “Action Plan on the prevention and control of Nosocomial Infections 2010–2015.”12 Equations used in segmented regression for HA-MRSA and
CLABSI incidence variation are shown in Table 1. Incidences for successive 4-week surveillance periods were calculated from January 1, 2006, to March 31, 2015. The time intervals were based on data availability and publication date of MRSA guidelines; corresponding calendar timing of each interval and period are shown in Table 1. Due to well-established secular trends of decreasing rates of HAIs,7,8,15,22–26we chose a control comparator that would not be impacted by the change in MRSA guidelines: CLABSI rates. The coefficients of segmented regression include ßo, the
baseline rate at the start of surveillance, and ß1,ß2, and ß3, the coefficients for incidence change by 4-week periods during the respective time intervals (Table 1). The change in baseline incidence from interval 1 to interval 2, is denoted by int2 with the coefficient ß4; similarly, the change in baseline incidence from intervals 2 to 3, is denoted by int3 and the coefficient ß5. All coefficients were adjusted for autocorrelation for counts by incorporating an error term for short-term (4 months) effects of guidelines on incidence change, as specified by Schwartz et al27 and Katsouyanni et al.28 The duration of 4 months was empirically estimated by examining residual function plots. The outcomes of interest from segmented regression models were the incidence rate ratios (IRRs) for CLABSI and HA- MRSA BSI. The IRR is defined as the ratio of rates for any single time segment compared to the previous one. The IRR was modeled for (1) the ratio of any single 4-week period compared to the previous period, and (2) the ratio of baseline
rates from one interval to the next. The covariate of interest was time, as measured by periods (4-week surveillance inter- vals). Models were run for all facilities and separately for teaching and nonteaching facilities. Subgroup analyses were also performed between full and partial participators in sur- veillance. We completed 2 sensitivity analyses to account for the HA definition change that occurred for HA-MRSA BSI surveillance: (1) April 1, 2013, was included as a third break point and (2) an abridged dataset excluding data collected after April 1, 2013 (Online Supplemental Appendix). All statistical calculations were performed using Stata version 14 software (StataCorp 2015, College Station, TX).
results Incidence Rates of HA-MRSA and CLABSI
Table 2 summarizes the annual incidence rates of HA-MRSA and CLABSI. Adult teaching facilities had higher incidences than nonteaching facilities. The HA-MRSA incidence decreased in teaching facilities from 9.56 in 2006 (95% CI, 8.34–10.9) to 1.86 cases per 100,000 patient days in 2015 (95% CI, 0.85–3.53). For nonteaching facilities, the incidence remained stable during the study period: 3.42 (95% CI, 2.70–4.37) in 2006 and 2.79 cases per 100,000 patient days (95% CI, 1.56–4.60) in 2015 (Table 2). CLABSI incidence was also higher in teaching facilities than in nonteaching facilities. Incidence rates decreased in both facility types: adult teaching CLABSI incidence dropped from 2.24 (95% CI, 1.86–2.67) to 0.68 cases per 1,000 CVC days (95% CI, 0.35–1.20), while adult nonteaching incidence dropped from 1.71 (95% CI, 1.19–2.38) to 0.46 cases per 1,000 CVC days (95% CI, 0.13–1.19). No significant changes in CLABSI incidence were observed between full and partial participator subgroups. For HA-MRSA, significant differences were seen in 2007 and 2011 for nonteaching facilities and in 2007 for teaching facilities. The addition of new facilities to the small number of partial participators (8% of total facilities) may account for these differences. The results shown in Table 2 include both partial and full participators.
Segmented Regression for HA-MRSA and CLABSI
Table 3 lists coefficients and IRRs for all facilities for each interval, separated by the 2 break points (April 1, 2007, and January 3, 2010). In terms of quantification of the incidence trends, when looking at all adult facilities, IRR per 4-week period for HA-MRSA was not different from 1.0 during interval 1, but it was significant at 0.991 during interval 2 (95% CI, 0.982–1.00) and during interval 3 at 0.990 (95% CI, 0.986–0.995), corresponding to decreases of 0.9% and 1.0% per 4-week period, respectively. Cumulatively, we estimated 25% and 22% relative rate reductions during intervals 2 and 3, respectively. By facility type, the significant reductions were observed only in teaching facilities, which had an IRR of 0.989
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