Infection Control & Hospital Epidemiology
units but also in pediatric units in Greece. The secondary objective was to assess the impact of sampling on other mea- sures related to HAIs, such as central-line utilization (CLU) ratios and CLDs.
Methods Sampling of denominator data
Daily denominator data were collected for 6 consecutive months in 33 units from 14 hospitals across Greece that participate voluntarily in a initative called “Prevention of Hospital- Acquired Infections in Greece” (PHIG). One of the ultimate goals of this initiative is the reduction of CLABSI rates nationally. More specifically, 12 neonatal intensive care units (NICUs), 6 pediatric oncology units (Ped-ONCs), 4 pediatric intensive care units (PICUs,) and 11 adult units provided these data. In addition, 7 of these were hospitals with academic medical units. CLDs and patient days (PTDs) were collected manually on a daily basis at the same time of the day in every unit. The number of CLABSIs was also reported by all partici- pating units, corresponding to the period during which the denominator data were collected. CLABSI rates and CLU ratios were calculated based on the CDC 2014 criteria.7 From the original set of daily denominator data, 3 sampling strategies with 32 possible permutations were evaluated as follows: (1) 1 fixed day per week (7 permutations), (2) 2 fixed days per week (21permutations),(3) 1weekpermonth(4permutations). CLDs and PTDs for each month were estimated for each sam- pling permutation as follows:
Estimated CLDs= Number of CLDsin the sample Number of sampled days per month ´ 30
Estimated PTDs= Number of PTDs in the sample Number of sampled days per month ´ 30
The estimated CLDs and PTDs were used to calculate monthly CLABSI rates and monthly CLU ratios for each sampling per- mutation as follows:
Estimated CLABSI rate= Number of CLABSIs Number of estimated CLDs ´ 1; 000
Estimated CLU ratio= Number of estimated CLDs Number of estimated PTDs
Statistical analysis
The accuracy of the estimated monthly CLABSI rates, CLDs, and CLU ratios was assessed by calculating the percentage error (PE) as follows:
PE of estimated monthly CLABSI rates=
Actual CLABSI rateestimated CLABSI rate Actual CLABSI rate
´ 100
The distribution of PE of monthly CLABSI rates is presented with medians and percentile range (5%–95%). The absolute and rela- tive frequencies (%) of months with PE ≤5% are also presented. Furthermore, intraclass correlation coefficients (ICCs), Bland- Altman plots, and percentages of months that are outside the limits of agreement were also calculated to assess the agreement between estimated and actual CLABSI rates.
Variable No. of units
No. of months No. of PTDs No. of CLDs
No. of CLABSIs Pooled CLU ratio
NICUs 12 71
1211 Sampling permutations that most frequently provided months
with PE ≤5% were selected and further examined. Linear mixed- regression models were used to compare the CLABSI rate PEs between these selected sampling permutations, taking into account that months were nested within units. Sensitivity analysis was conducted to detect differences in estimation between months with low and high CLDs. We used 75 CLDs as a cutoff, as proposed by the CDC.13 All statistical analyses were stratified by type of unit: NICU, PICU, Ped-ONC, Adult. All analyses were conducted using STATA version 13 software.
Results
The original denominator dataset included information from 71 months from NICUs, 34 months from Ped-ONCs, 24 months from PICUs, and 66 months from adult units. An overview of descriptive characteristics of the types of participating units is presented in Table 1.
Estimation of CLABSI Rates
The distribution of monthly CLABSI rate PEs and the number of months with CLABSI rate PEs ≤±5% by sampling permu- tation are provided in Figure 1 and Table 2. Sampling over 7 consecutive days, ie, 1 week per month (either the first, second, third, or fourth week of each month; permutations: weeks 1–4in Fig. 1) provided the least accurate estimates of CLABSI rates (ie, the distribution of PE was very wide). Day-pair samples pro- vided the most accurate estimates across all types of units. More specifically, in NICUs the proportion of months with CLABSI rate PE ≤5% was highest in the following pairs: Monday–Friday (85.9%), Tuesday–Wednesday (85.9%), Wednesday–Saturday (85.9%), Wednesday–Sunday (88.7%), and Thursday–Sunday (88.7%). In Ped-ONCs, the highest proportions were noted in the following pairs: Monday–Thursday (91.2%), Tuesday– Saturday (91.2%), Thursday–Saturday (91.2%), Friday–Saturday (91.2%), Friday–Sunday (91.2%), Monday–Tuesday (94.1%), and Monday–Friday (97.1%). In PICUs, the highest proportions were noted in the following pairs: Thursday–Friday (91.7%) and Friday–Saturday (87.5%). Lastly, in adult units, the highest proportions were noted in the following pairs: Wednesday–
Table 1. Descriptive Characteristics of Types of Units Participating From the 14 Hospitals
Ped- ONCs PICUs
6 34 4 24
Adult Units
11 66
41
38,533 11,056 3,094 49,583 6,232 9,099 2,124 11,441 7
18 0.16 Pooled CLABSI rate per 1,000 CLDs 6.58
0.82 0.77
0.69 8.47
73
0.23 6.38
Note. PTDs, patient days; CLDs, central-line days; CLABSIs, central-line–associated blood- stream infections; CLU, central-line utilization; NICUs, neonatal intensive care units; Ped- ONCs, pediatric oncology untis; PICUs, pediatric intensive care units.
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