Legionella Testing and Sampling: Legionnaires' Outbreaks

The following presentation looks at Legionella testing and water sampling and how to make a sampling plan for Legionnaires’ outbreak investigations in the USA. The presentation uses the example of a legionellosis outbreak at a hotel to demonstrate how to develop a clear and well organised water sampling plan which will help minimise the cost of testing as well maximising your ability to make good recommendations once test results are available. The video, the third in a series published by the US Centers for Disease Control and Prevention (CDC) gives an introduction to environmental health and engineering measures for legionellosis outbreak investigations in the USA.

Legionella Testing & Water Sampling

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.

Water Sampling Plans

Water sampling is an important step in an outbreak investigation, but you need to create 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 colonisation.

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.

Example – Legionellosis Outbreak at a Hotel

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 3^rd, 4th and 8^th 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 one serves floor 1 through 5. Floors 6-10 are served from a separate riser that draws from the storage tank which is fed from hot water heaters one and two. The riser serving floors 6-10 has a re-circulating hot water line while the riser serving floors 1-5 does not. The 3^rd 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 let’s tally the number of samples we will need.

Water Sample Collection

You should collect two types of samples from each outlet or device – a 1 litre bulk hot water sample, and a swab of the biofilm, because Legionella do not grow in cold water below 77degrees 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 two 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.

Where did the Case Patients Visit?

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, 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 and far from the hot water heaters on the upper floors. In this example we’d sample on the 6^th and 10^th floors.

Identifying Water Sampling Sites

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 organised sampling plan will help minimize the cost of testing as well maximising your ability to make good recommendations once test results are available.

How to Make a Sampling Plan for Legionellosis Outbreak Investigations – U.S Department of Health and Human Services; Centers for Disease, Control and Prevention

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