Legionella outbreak in a care home: the first case is the signal

Why the first case matters

The two largest outbreaks reported to the RKI up to 2021 happened in Ulm and in Warstein, and both were linked to evaporative cooling systems, which get rid of heat by letting water evaporate (Epidemiologisches Bulletin 42/2021). Ulm had around 60 cases, Warstein more than 160. Most outbreaks look nothing like that. They are small and unremarkable.

Most reports are of single cases of Legionnaires' disease. Only about 5% of each year's cases belong to a cluster, meaning several cases that probably share a source. And more than half of those clusters (54%) involve just two people.

The catch: months can pass between two cases in the same cluster. On top of that, infections picked up in hospitals and care homes don't follow the seasons, even though overall numbers peak in summer and autumn. If you wait for a second case before acting, you may already have lost months.

That is why the RKI's advice kicks in earlier (RKI guidance for the public health service). If someone who fell ill was in the home during the likely period of exposure, an on-site investigation should promptly establish how the infection happened and, if needed, cover the building's water pipes as well, to help stop further cases. According to the RKI, it makes no difference to this investigation whether your last Legionella test came back clean.

In practice, the issue can land on your desk in two ways: through a resident who falls ill, or through a lab result, even when nobody is ill at all. If a sample reaches the action value of 100 colony-forming units (CFU, the unit labs use to count bacteria) per 100 ml, the German Drinking Water Ordinance sets out what happens next. Our article on what to do about Legionella walks through those steps, from notifying the Gesundheitsamt (local public health authority) to the follow-up test.

What to settle in writing beforehand

Once a case comes to light, there's little time to think things through. The public health authorities involved in the Brandenburg outbreaks drew a clear lesson from them: the technical team, infection control and the Gesundheitsamt should agree on measures against Legionella together and write them down, along with an outbreak plan. Staff should also be trained on it.

That advice was written for a hospital. In a care home, different people sit around the table, but the job is the same. And you already have a place to put it: care homes have to set out their infection control procedures in a hygiene plan anyway (Section 35(1) of the Infection Protection Act, IfSG). That is exactly where the answers to four questions belong, ideally before anyone falls ill:

• Who decides? Who is allowed to close a shower, have point-of-use filters fitted or have the pipes disinfected, including at the weekend? (Point-of-use filters sit directly on the shower or tap.) Closing showers and disinfecting pipes, in particular, should be agreed in advance between your maintenance team, your hygiene lead and the Gesundheitsamt.
• Who calls whom? Who speaks to the Gesundheitsamt, and who lets residents, relatives and staff know?
• Who takes samples, and where? Routine samples need sampling points, conditions and intervals that are set down in writing. The technical team, infection control and the Gesundheitsamt should agree on them together, with the lab where relevant. If there is a specific reason, such as a resident falling ill, extra sampling points are added to find out whether the water is behind it.
• Who watches for pneumonia? For hospitals, the authorities advise tracking hospital-acquired pneumonia systematically and considering Legionella as a possible cause. In a care home, that becomes: who notices when residents go into hospital with pneumonia, and who follows up on whether Legionella is the cause?

Our page for care homes covers what else drinking water hygiene involves in a home. Our page on drinking water hygiene in hospitals has more.

Questions for your maintenance team

You don't need to be an engineer to raise these at your next meeting. And if nobody has a clear answer to one of them, you know where to start.

• Which showers hardly ever get used, even in occupied rooms, for example because a resident is washed in bed? And where is it recorded when the water last ran there?
• Who flushes those showers (runs off the standing water so that fresh water comes through), and where is each flush logged? Our article on hygiene flushing explains how often and for how long.
• Which areas stood empty for a while, were refurbished or newly occupied, and how were they brought back into use? The Brandenburg outbreaks happened in exactly that kind of space: newly occupied parts of a building.
• Are there taps or showers where the cold water is no longer properly cold? Our article on how Legionella multiply explains why that matters.
• When was the water last tested for Legionella, and where is the report kept?
• Who sees a lab result first, and who reads it the same day?

For the showers, you can hand part of this list over. The hygiene flush device for exposed shower installations from Aqvior sits behind the existing shower fitting and recognises when a shower has gone 72 hours without use, including in occupied rooms or in a wing that is currently empty. It then flushes the shower as a precaution. If needed, the interval can be set shorter.

Every flush is logged in the web dashboard with its time, duration and water temperature, and stays available for ten years. Whoever works with the dashboard in your facility gets a monthly overview, and the compliance record downloads as a PDF in one click. So you can see at any time which shower last ran and when, without anyone keeping a list.

Frequently Asked Questions

When does it count as a Legionella outbreak?

From two cases that probably share a source. The RKI treats two or more cases of Legionnaires' disease as a cluster if they occur no more than two years apart and the people affected were either infected in the same place or live in flats or houses supplied by the same building water system. So a single case is not yet an outbreak, but it is already a reason to take a close look.

How common are Legionella outbreaks in care homes?

The RKI reports cases in care homes, not outbreaks, and their share is small but has grown. In 2020, the RKI counted 39 of the 1,281 reported cases as linked to care homes, meaning they were in people who lived in a residential or nursing home for older people: 3.0%. In 2010 it was 9 out of 692 cases, or 1.3%. According to the RKI, an ageing population explains only part of that rise.

Should a single Legionella case in a care home be investigated?

Yes. The RKI advises it from the very first case. If a resident with Legionnaires' disease was living in the home when they were most likely infected, the home should be investigated straight away, including the building's water pipes if needed. An earlier clean result doesn't change that. Ideally, who does what at that point is already written into your hygiene plan.