Rule out procedure first, then stop blaming it
Technique is the obvious first suspect and worth reviewing properly. But once a full decontamination cycle has been run correctly and contamination returns within weeks, continuing to review technique is looking in the wrong place. Something in the unit is providing a reservoir or a route in.
Water pan and humidity system
The humidity reservoir is the most common reservoir for recurring contamination. Anything that lets it sit longer than it should, or lets biofilm establish in a place cleaning does not reach, will reseed the chamber after every cycle.
Door gaskets and seals
Gasket surfaces develop micro-damage that harbours organisms and resists surface cleaning. A gasket that also no longer seals evenly allows both contamination and humidity loss, which is why condensation patterns at the door are worth paying attention to.
Airflow, filtration and ducting
Contamination can establish in ducting and behind panels where routine cleaning does not reach and a decontamination cycle may not fully penetrate. Filters that are past their service life stop doing the job they are there for.
Decontamination cycles that do not complete
A cycle that ran is not the same as a cycle that worked. If the cycle did not reach or hold its target conditions — because of a sensor fault, a seal problem or a control issue — you have a documented decontamination and a still-contaminated incubator. Verification after the cycle is the only way to know which you have.
When to call
If contamination has returned twice after correct decontamination, stop repeating the cycle and have the unit inspected. Continuing to run cycles costs time, costs cultures, and does not address a mechanical cause.
