In the midst of the investigation into the Legionnaires' disease outbreak at University of Washington Medical Center, the Seattle-based hospital said last week three heater-cooler devices tested positive for Legionella bacteria. Now, the hospital says all nine of the devices at the hospital tested positive for the bacteria.
Here are six things to know about the outbreak, heater-cooler devices and their potential role in spreading Legionella bacteria.
1. Five patients in the hospital's Cascade Tower have contracted Legionella infections. Two of those patients have died.
2. After the first four infections were detected, the hospital tested the environment and found an ice machine and two sinks in the Cascade Tower tested positive for the bacteria. Then, on Sept. 16, three heater-cooler devices, which are used to warm and cool patients' blood during some heart surgeries, also tested positive for Legionella.
3. On Tuesday, UW Medical Center said further tests detected Legionella in not just three, but all nine of its heater-cooler devices.
4. Despite the presence of the bacteria in all of the devices, UW Medicine does not believe they are the source of the human infections, instead blaming the sinks and ice machine. The system listed the following reasons for that belief:
- Heater-cooler devices were used on two of the five affected patients
- The timing of the onset of the infections in those two patients was outside of the typical Legionella incubation period for one patient and at the end of the period in the other
- There is no past history for Legionella infecting humans from the machines
- Water in the units does not come into contact with the patient at any time — it circulates in the device itself
- Breathing machines used on patients in the operating room pull air from a protected supply that is separated from other OR air, including where the heater-cooler devices are
5. Even though the hospital does not believe the devices spread Legionella to patients, it is enhancing the cleaning of the devices to protect patients. Those steps include:
- Draining, cleaning and flushing the machines after each use with a chlorine solution, even though manufacturers recommend cleaning them just once a quarter
- Using sterile water in the units
- Using ice made with filtered water in the units' cooler components
6. Heater-cooler machines have been in the news recently separate from this Legionnaires' disease outbreak. The devices, used by hospitals across the country during some heart surgeries, have been pointed out as the cause of nontuberculous mycobacterial infections in patients at several hospitals. The Food and Drug Administration issued a warning about the devices' safety, as has the CDC.