Hospital's water system implicated in Mycobacterium gordonae pseudo-outbreak

Abstract

ISSUE: As rapid identification of acid-fast bacillus (AFB) species is necessary in the control of nosocomial outbreaks of <i>Mycobacterium tuberculosis,</i> monitoring of AFB-positive cultures is an important part of infection control surveillance. A sharp rise in the rate of positive AFB cultures was seen at this medical center between March and September 2004. Review of isolates revealed a total of 15 out of 40 positive AFB cultures were identified as <i>M. gordonae.</i> In this time period, the isolation rate of <i>M. gordonae</i> was 14.0/1000 cultures versus the 2003 rate of 3.5/1000 cultures. Concentrated sputum specimens were AFB smear negative, and culture positive patients were non-symptomatic which indicated a pseudo-outbreak. PROJECT: Laboratory reagents were eliminated as a potential source of the increase in <i>M. gordonae.</i> As water for this facility is held in two 250,000-gallon underground tanks built in the late 1940s, ground water contamination from heavy seasonal rains was considered as a possible source of this pseudo-outbreak. Investigation showed that the normal bi-weekly rotation of water in the tanks, between potable water and fire system water, was not being performed on schedule, and chlorine levels decreased out of effective range within the scheduled rotation period. In September 2004, the facility implemented the following multidisciplinary team recommendations: 1) cease rotation of tanks, and designate only one tank for potable water; 2) institute regular monitoring of holding tank potable water for adequate chlorine levels; 3) install a new tank lid and seal to decrease contamination from ground water; and 4) install a 0.5 micron filter in the water line between the potable water holding tank and the facility. RESULTS: Following these interventions, environmental cultures of the facility water were negative for <i>M. gordonae,</i> and no <i>M. gordonae</i> positive sputum cultures have been noted. LESSONS LEARNED: Concurrent monitoring by trained infection control professionals identified clustering of non-pathogenic mycobacteria isolates. Due to this facility's high-risk practice (i.e., underground water tanks) appropriate surveillance indicators are needed to reduce the potential for oropharyneal colonization from a contaminated water source. Stringent engineering controls were implemented to decrease the potential for human error, while protecting a medically complex, at-risk patient population.