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Background
Heater-cooler units (HCUs) are frequently used in cardiac surgery and have been implicated
in nontuberculous Mycobacterium (NTM) infections. A patient developed a NTM infection
after undergoing cardiac surgery and the HCU was evaluated for an epidemiologic link.
This study assesses challenges of interpreting significance of low numbers of colony
forming units (CFU) of NTM in the water tank of a HCU.
Methods
The HCU was removed from service. A 220 milliliter (ml) water sample was collected
from the tank drain of the HCU after disinfection and sent to an outside laboratory
to evaluate for NTM. NTM was identified in the initial specimen. The HCU was re-disinfected
and re-cultured. Repeat cultures grew the same NTM as the first sample. Disinfection
practices were reviewed and all HCU disinfection aligned with manufacturer's instructions
for use. With continued growth of NTM, the HCU was sent to the manufacturer and internal
water paths were replaced. Upon return of the HCU to the hospital, it was disinfected
and cultured.
Results
Initial water sample grew 14 CFU/ml of Mycobacterium immunogenum. This species did
not match the patient's clinical isolate. Repeat culture after disinfection grew 36
CFU/ml of the same organism. Water cultures obtained after the manufacturer replaced
the HCU's internal water paths grew 14 CFU/ml of the same NTM. After review of Centers
for Disease Control and Prevention (CDC) guidance regarding acceptable levels of colony
counts in dialysis and endoscopes, in addition to no epidemiological link of this
NTM species to any patient infections, the HCU was returned to service.
Conclusions
Currently, there is no standardized threshold for NTM in HCUs or in municipal water
supply. The use of filters may not eliminate all NTM in tap water. A standardized
threshold needs to be set for allowable limits of recovered NTM in HCUs in order to
return to service safely.
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Copyright
© 2022 Published by Elsevier Inc.
