mycobacteria risks from water and ice machines 795
figure 1. Epidemiological Curve showing onset of outbreak of pediatric hematopoietic stem cell transplant (HSCT) patients with positive rapidly growing mycobacteria (RGM) isolates starting shortly after the move to a new children’s hospital building.
in these 2 periods, that is, 0 cases per 11,468 inpatient days (January 2009 to March 2011) compared with 15 cases per 6,920 inpatient days (April 2011 to April 2012). Using an exact-rate ratio test (assuming a Poisson distribution is appropriate), rate ratio is estimated as 0.00 (95% CI, 0–0.168; P<.001). Finally, consumption of hospital DWIM water and ice was prohibited for pediatric HSCT patients, and commer- cial bottled water was thereafter provided to these patients. Bottled water from multiple distributors was tested for bacterial colony counts. The brand with the least colony for- mation (ie, mean <1CFU/mL) was used thereafter for HSCT patients. Since the bottled water intervention began in the pediatric HSCT population 4 years ago, RGM has not been detected in this patient population in our hospital. Prior to patient occupancy in the newhospital, bacterialHPC
cultures with the highest bacterial HPCs (ie,>100,000CFU/ mL) were identified in the drinking water and ice from the DWIMs. Isolates from DWIM cultures were identified as M. chelonae or M. abscessus and M. mucogenicum or M. phocaicum.3 Samples revealed acceptable colony counts (1–2,610CFU/mL) at the point of water entry into the new hospital; most HPCs were <500CFU/mL, suggesting escalation within the hospital water distribution system. Sampling of water at multiple points within the hospital showed acceptable HPCs up to the entry point of water into the DWIMs. When HPCs from drinking water and ice from the DWIMs
levels in first-drop water ranged from 350 to 3,400CFU/mL. Disinfection of the domestic water system was performed twice using premixed chorine (50 ppm) that was allowed to dwell for 12 hours, followed by flushing. Initial disinfection 14 weeks prior to occupancy reduced bacterialHPC, from1,980CFU/mL to 47CFU/mL, but higher bacterial counts returned within 2 weeks. Repeating disinfection 4 days prior to occupancy reduced colony counts from 1,720CFU/mL to 47CFU/mL. After the new hospital had been occupied for 6 months, an
increase inRGMisolates (Mycobacteriumchelonae, M. abscessus, and M. immunogenum) in the clinical cultures of pediatric HSCT patients was observed, and water testing began.3 Water
in the new and the old hospitals were compared, significant differences were observed. The new hospital’s DWIMs were similarly designed and were from the same manufacturer, but they held twice the volume. The old hospital unit had a single 12-pound ice machine serving 25 patients. The new hospital had four 25-pound ice machines serving 24 patients and, thus, an 8-fold increase in the volume of DWIM. The old hospital’s DWIM had counts consistently between 0 and 5,000CFU/mL in the water and between 0 and 4,000CFU/mL in the ice. The new hospital’s HSCT unitDWIMat baseline had HPCs as high as 300,000CFU/mL in water and 780,000CFU/mL in ice.
Interventions
All four 25-pound ice machines were replaced with 2 smaller 12-pound ice machines per hospital floor. The manufacturer
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