Two-Phase Hospital-Associated Outbreak of Mycobacterium abscessus: Investigation and Mitigation

Abstract

Background: Nontuberculous mycobacteria (NTM) commonly colonize municipal water supplies and cause healthcare-associated outbreaks. We investigated a biphasic outbreak of Mycobacterium abscessus at a tertiary care hospital.

Methods: Case patients had recent hospital exposure and laboratory-confirmed colonization or infection with M. abscessus from January 2013 through December 2015. We conducted a multidisciplinary epidemiologic, field, and laboratory investigation.

Results: The incidence rate of M. abscessus increased from 0.7 cases per 10000 patient-days during the baseline period (January 2013-July 2013) to 3.0 cases per 10000 patient-days during phase 1 of the outbreak (August 2013-May 2014) (incidence rate ratio, 4.6 [95% confidence interval, 2.3-8.8]; P < .001). Thirty-six of 71 (51%) phase 1 cases were lung transplant patients with positive respiratory cultures. We eliminated tap water exposure to the aerodigestive tract among high-risk patients, and the incidence rate decreased to baseline. Twelve of 24 (50%) phase 2 (December 2014-June 2015) cases occurred in cardiac surgery patients with invasive infections. Phase 2 resolved after we implemented an intensified disinfection protocol and used sterile water for heater-cooler units of cardiopulmonary bypass machines. Molecular fingerprinting of clinical isolates identified 2 clonal strains of M. abscessus; 1 clone was isolated from water sources at a new hospital addition. We made several water engineering interventions to improve water flow and increase disinfectant levels.

Conclusions: We investigated and mitigated a 2-phase clonal outbreak of M. abscessus linked to hospital tap water. Healthcare facilities with endemic NTM should consider similar tap water avoidance and engineering strategies to decrease risk of NTM infection.

Keywords: Mycobacterium abscessus; hospital outbreak; hospital water safety; infection control; nontuberculous mycobacteria.

Figure 1.

Epidemic curve of Mycobacterium abscessus colonization or infection. A, Initial epidemic curve including the baseline time period (January 2013–July 2013) and phase 1 of the outbreak (August 2013–May 2014). B, Final epidemic curve portraying key events and incident cases over the full 3-year study period, including phase 2 of the outbreak (December 2014–June 2015). Cases were stratified by patient type. The timeline of both epidemic curves was constructed from dates of culture collection, which in some cases occurred months after date of suspected patient inoculation. In particular, cardiac surgery cases that were identified after the 9 May 2015 heater-cooler unit disinfection protocol changes were either linked to cardiac surgeries performed before these protocol changes (n = 3) or were thought to be unrelated to the cardiac surgery (n = 1).

Figure 2.

XbaI pulsed-field gel electrophoresis (PFGE) of patient and environmental isolates of Mycobacterium abscessus obtained from 2007 through 2015. A, Isolates selected for this panel demonstrated gene sequencing and/or variable number tandem repeats (VNTRs) consistent with outbreak clone A [erm(41) gene: subspecies abscessus, type VI; rpoβ gene: subspecies abscessus, C→T mutation at base pair 207; VNTR: primer TR155, 5 copies]. The panel includes 2 preoutbreak patient isolates from 2010–2012 (lanes 1, 2), 4 case patient isolates from phase 1 of the outbreak period (lanes 3, 4, 5, 6), 2 case patient isolates from phase 2 of the outbreak period (lanes 7, 9), 1 patient isolate from the outbreak period that did not meet the case definition (lane 8), 1 environmental isolate from phase 1 (lane 10), and the M. abscessus subspecies abscessus type strain—ATCC19977^T (lane 11). The 9 patient isolates included samples from bronchoalveolar lavage (n = 5), blood (n = 1), pleural fluid (n = 1), sputum (n = 1), and sternal wound (n = 1). All clinical and environmental isolates (lanes 1–10) were clonal [30]. Isolates were indistinguishable or closely related except isolate 8 (possibly related), and all 10 isolates were unrelated to the M. abscessus subspecies abscessus type strain (lane 11). Seven additional environmental isolates from phase 1 were also indistinguishable (data not shown). B, Isolates selected for this panel demonstrated gene sequencing consistent with outbreak clone B [erm(41) gene: subspecies massiliense; rpoβ gene: subspecies abscessus]. The panel includes 4 preoutbreak patient isolates from 2007 through 2013 (lanes 1, 2, 3, 4), 3 case patient isolates from phase 1 of the outbreak period (lanes 5, 6, 7), 1 case patient isolate from phase 2 of the outbreak period (lane 9), 2 patient isolates from the outbreak period that did not meet the case definition (lanes 8, 10), and the M. abscessus subspecies massiliense type strain—CIP108297^T (lane 11). The 10 patient isolates included samples from bronchoalveolar lavage (n = 4), blood (n = 2), pleural fluid (n = 2), soft tissue (n = 1), and sputum (n = 1). All patient isolates (lanes 1–10) except isolate 10 were clonal [30]. Patient isolates other than isolate 10 were indistinguishable or closely related except isolates 1 and 9 (possibly related). Isolate 6 had poor image resolution but appeared related. All 10 isolates were unrelated to the M. abscessus subspecies massiliense type strain (lane 11).