Fourteen sampling sessions were conducted over a seven-month period between 21.11.2018 and 06.06.2019, resulting in 280 shower water samples and 280 surface swabs taken from drains. Seven out of the ten showers on Ward A (non-augmented care unit) were dedicated to bed bays where the showers were shared between four patients while the remaining three showers belonging to SIRs. All ten showers on Ward B (augmented care unit) belonged to single isolation rooms.
Shower water and drain contamination
The presence of P. aeruginosa contamination in shower waters and drains during the study are shown in Table I. Where P. aeruginosa was isolated, there were >300CFU/100mL in all cases.
At the beginning of the study, all showers from ward A (non-augmented care) had long hoses (EPDM composition-1.2m) except for one (Shower #6) with a short hose (PVC-0.8m). Four showers were fitted with a point-of-use filtration device (Showers #1, #2, #4 and #5), four were plastic-chrome shower heads (Showers #3, #8, #9, #10) and two were antimicrobial silver-impregnated showers (Showers #6 and #7). Although measures against pseudomonas were not stipulated in a general ward, there had been earlier outbreaks of pseudomonal wound infection. All showers in ward B (augmented-care) were antimicrobial silver-impregnated showers with long hoses (PVC-1.2m) and without a filter.
During the course of the study, shower hoses were changed three times in Ward A (non-augmented care unit) (Table I.A) and two times in Ward B (augmented-care unit) (Table I.B). Initial sampling results showed that 4/10 shower outlets (40%) were contaminated with high counts (>300CFU/100mL) of P. aeruginosa in Ward A, whereas 8/10 (80%) of them were contaminated in Ward B. By the final sampling week, 5/10 shower outlets (50%) and 9/10 shower outlets (90%) were contaminated with P aeruginosa in Ward A and Ward B respectively.
P. aeruginosa was isolated from 5/20 drains at the start of the study and 10/20 drains at the end. P. aeruginosa in the drains did not always coincide with shower water contamination (Table I). Drains harboured many bacterial species. Other than P aeruginosa, species growing on C-N agar media, were P. alcaligenes, P. fulva, P. guariconensis, P. mosselii, P. nitroreducens, P. stutzeri; Aeromonas hydrophilia, Aeromonas caviae, Citrobacter braaki, Citrobacter freundii, Achromobacter insolitus, Achromobacter denitrificans and Enterobacter cloacae.
Table I. The effect of introducing unused antimicrobial shower head-hose units (interventions) into non-augmented care (Table I.A) and augmented care (Table I.B) wards on the presence of P. aeruginosa in showers (green) and corresponding drains (orange) over a 29-week period.
*Denotes POU filter shower heads in-situ
Presence of P. aeruginosa is indicated by green (shower) and orange (drain) highlighted cells respectively. Blank cells represent no contamination by P. aeruginosa. Quarterly shower hose changes are marked by column.
At the start of the study, shower head and hose types varied between wards. Ward A shower heads: #1,#2,#4 and #5 had point-of-use (membrane) filters with long hose; shower heads #3, #8, #9 and #10 were plastic chrome (non-antimicrobial) with long hose (EPDM); shower heads #6 and #7 were antimicrobial silver-impregnated bodies with short and long hoses (PVC) respectively. All showers on Ward B were antimicrobial silver impregnated shower heads mounted on a long hose (PVC).
P. aeruginosa colonised both shower-waters and drains simultaneously in 79/260 occasions (~30%) with presence in only the drain or shower water on 11/260 (~4%) and 81/260 (~31%) of occasions respectively. In 89/260 occasions (~34%), P. aeruginosa did not present in the shower water or drain. A cross-tabulation of P. aeruginosa presence in the shower environment showed contamination of one site (shower or drain) correlated with occurrence in the adjacent site/outlet (chi-square: p <0.001).
Associations between ward type and exposure (time)
a) Approach 1 – Occurrence of contamination over time
Logistic multi-level regression modelling demonstrated a significant association between duration of use in the clinical setting and occurrence of P. aeruginosa in shower waters (P=0.004) and drains (P=0.03); these are depicted in figure 1 (showers) and figure 2 (drains).
For every week elapsed, the odds for colonisation with P. aeruginosa in the non-augmented care setting increased by 19% in shower waters (OR= 1.19; CI= 1.09 - 1.31, P<0.001) and 18% in the drains (OR = 1.18; CI= 1.09 - 1.30, P<0.001). Odds for P. aeruginosa colonisation over time remained unchanged in the augmented care wards for showers (OR= 0.95; CI= 0.84 - 1.07, P=0.42) and drains (OR= 1.04; CI= 0.98 - 1.11, P=0.23). Graphical illustrations of the fitted change over time are shown in Figure 1 for showers, and for Figure 2 for drains.
b) Approach 2 – Occurrence of colonisation between interventions
The frequency of contamination of shower waters and drains with P. aeruginosa and odds of occurrence between interventions (introducing antimicrobial shower head-hose units) in augmented and non-augmented care wards is shown in table II. The pre-intervention (control) phase comprised the number and percentage of measurements where P. aeruginosa was present for each sample site/ward/timepoint combined. The first and second intervention depict the odds of P. aeruginosa occurrence in each period relative to the odds for the control period.
Table II: Comparison of frequency and odds of occurrence of P. aeruginosa in shower waters and drain surfaces following interventions relative to a pre-intervention (control) phase.
Relative to the pre-intervention phase, the likelihood of shower water and drains in the non-augmented care setting (ward A) becoming colonised with P. aeruginosa increased over time (p<0.05), with the highest density of colonised showers/drains after the second intervention.
Colonisation of showers and drains in the augmented care ward (Ward B) persisted at high frequency regardless of the intervention.
Antimicrobial Susceptibility profiles
Of 274 positive P. aeruginosa samples, 117 were isolated from Ward A (69 shower head water; 48 shower drain) and 157 were isolated from Ward B (105 shower water and 52 shower drain). ASTs were performed on a 50% sample (Ward A shower water n=35; Ward A shower drain n=24; Ward B shower water n=53; Ward B shower drain n=26).
In the non-augmented care setting, cefepime resistance in P. aeruginosa from shower water declined after the first and second interventions (P<0.05) relative to the pre-intervention isolates with no changes observed in drain isolates (see supplementary Table 2). No other resistance profiles changed in relation to interventions on this ward.
The first set of analyses examined changes over the course of the study for measurements taken from showers in Ward A. A summary of the analysis results is shown in Supplementary Table 1.
Approximately 50% of the sample population of P. aeruginosa isolated from shower waters in the augmented care wards were resistant to imipenem in the pre-intervention phase. Frequency of imipenem-resistance declined to 12% and 31% after the first and second intervention respectively (P<0.05). No other significant differences were observed for the other antibiotics.
The final analyses compared between time periods for data from drains in Ward B. The results are summarised in Supplementary Table 4. Drains in the augmented care wards harboured P. aeruginosa with resistance to aztreonam in 75% of occasions during the pre-intervention phase that declined to 20% and 0% after subsequent interventions (first and second intervention respectively). Similarly, ciprofloxacin resistance in drain-derived P. aeruginosa declined after the interventions relative to the pre-intervention phase (P<0.05). Statistically significant differences between the three time periods were observed for ciprofloxacin, resistant measurements were most frequently seen in period 1, with a fewer in the subsequent time periods.