Correction of persistently positive dialysis surveillance cultures

ISSUE: Using Centers for Disease Control and Prevention (CDC)–recommended methods, this hospital centerʹs dialysis department conducts monthly microbiologic surveillance of water used for dialysis after being processed and conditioned in a reverse osmosis (RO) system. In December 2003, 2 days after changing carbon tanks and booster pumps, with intermittent bypass of the RO system, 2/2 surveillance cultures grew >100,000 colony forming units (cfus) of Pseudomonas aeruginosa. Despite immediate and repeated disinfection throughout the month, 4/11 cultures remained over threshold (range 120–380; mean 255 cfus). PROJECT: A multidepartmental project was undertaken to correct the contamination problem. The CDC and other resources were consulted. Multiple modes of disinfection, using paracetic acid, formaldehyde, and chlorine for varying dwell times were attempted without achieving acceptable levels. The carbon tanks and tubing were again replaced. The integrity and seal of the RO membrane was assessed by chemical marker and found to be sound. RESULTS: Surveillance cultures remained persistently over threshold until the membrane was replaced on February 13. Assays obtained 4 days after membrane replacement were under the threshold, but higher than the predicted baseline (average count <100 cfus). Subsequent assays (n = 65) obtained between February 24 and December 31 ranged between 0 and 100, with a cfu mean count of 7.7 ± 17.2. Endotoxin assays performed after replacing membrane were within normal limits. All patients dialyzed during the time of excessive bacterial counts were assessed, with none showing evidence of sepsis related to dialysis. LESSONS LEARNED: Because routine surveillance cultures can be effective to screen for system contamination, careful attention to CDC and Association of the Advancement of Medical Instrumentation (AAMI) collection and culture methods are necessary to provide accurate and timely microbiologic interpretation. New AAMI guidelines, published in 2004, provide a more sensitive threshold for action than earlier CDC guidelines. Hospitals should routinely perform surveillance cultures immediately following maintenance or other system disruption as these actions can dislodge biofilm and free bacteria. Persistent contamination after aggressive disinfection and routine maintenance may signal the need for a membrane change.