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Welcome to the third video in our series addressing environmental aspects of legionellosis outbreak investigations.
This video looks specifically at how to make a sampling plan and is meant to be used with the written guidance,
"CDC Sampling Procedure and Potential Sampling Sites".
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Water sampling is an important step in an outbreak investigation, but you need to create a plan for how to approach it.
Processing samples for Legionella culture can be very expensive and time-consuming.
You want to sample the sites that will be the most relevant and representative, with the smallest number of samples.
Sampling plans are based on the Environmental Assessment and the epidemiologic data
available, including case room numbers and exposures to aerosol-generating devices.
The purpose for sampling is to determine the source of transmission and the extent of colonization.
The team that develops the sampling plan should include, at a minimum, public health officials, the building owner or
manager, and the facilities manager. You will also need to have the floor plan and the premise plumbing schematic.
Let's look at an example of an outbreak in a hotel to illustrate how to use this information to create a sample plan.
Let's say we know the case-patients stayed on the 3rd, 4th, and 8th floors of the hotel. Two of the case-patients reported using the
whirlpool spa and the other two swam in the pool. All case-patients reported showering in their rooms.
The environmental assessment of the premise plumbing identified 3 hot water heaters and 1 hot water storage tank.
Hot water heater 1 serves floors 1-5. Floors 6-10 are served from a separate riser that draws from the storage tank, which is fed
from hot water heaters 1 and 2. The riser serving floors 6-10 has a recirculating hot water line, while the riser serving floors 1-5 does not.
The third hot water heater only supplies water to the laundry room.
The environmental assessment also revealed the following aerosol-generating devices:
A decorative fountain in the lobby, an indoor pool and spa, and a cooling tower on the roof.
In this example, letçs tally the number of samples we will need.
You should collect two types of samples from each outlet or device:
a 1-liter bulk hot water sample, and a swab of the biofilm. Because Legionella do not grow in cold water below
77 degrees F, it is generally not necessary to collect cold water from the premise plumbing for culture.
You should collect hot water samples from all outlets in case-patient rooms. If a room is unavailable, plan to sample a room next door.
Water outlets in a room far from the case-patient rooms should be sampled as well.
We need to sample the 2 hot water heaters and storage tank that serves guest rooms. We do not need to
sample the small hot water heater that serves only the laundry room, because no case-patients had exposure to this area.
All of the case-patients walked through the lobby, so we need to sample the decorative fountain.
Two case-patients did not report using the spa; however, the spa is located in the same enclosed space as the pool.
So, it could be a source of transmission for all case-patients and should be sampled.
Since there is a cooling tower on the roof of the hotel, all case-patients could have had exposure to it, so it should be sampled as well.
To ensure representative sampling of the premise plumbing, you should also take some samples that are close
to and far from the hot water heaters on the upper floors. In this example, we'd sample on the 6th and 10th floors.
Once you know which sites will be sampled, you can tally how many water bottles and biofilm swabs you'll need for sampling.
It is a good idea to bring a few extra with you just in case you run into something unexpected.
Developing a clear and well-organized sampling plan will help minimize the cost of testing while
maximizing your ability to make good recommendations once test results are available.
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