WATER HYGIENE AND SAFETY Extensive clinical data from Denmark
(Figure 2), which has one of the highest rates of documented Legionnaires’ disease cases in Europe, can help answer that question. In Demark, the use of the UAT to diagnose patients is rare. Instead, 80-90% of Legionnaires’ disease cases are initially diagnosed by polymerase chain reaction (PCR), meaning Legionnaires’ disease cases caused by both L. pneumophila and other species of Legionella are detected and reported.12
Yet the Danish data also
highlights the importance of focusing on L. pneumophila to protect from Legionnaires’ disease. Even where UAT is not used to diagnose patients, 93% of PCR-diagnosed cases in 2019 were caused by L. pneumophila, (including community- acquired, hospital/nursing home-acquired, and travel within Denmark cases).13
In fact,
only one case of Legionnaires’ disease out of the 112 that were culture-verified could be confirmed as a non-pneumophila species. In 2020, the result was very similar – 93% of PCR-diagnosed cases were caused by L. pneumophila, and only two patients could be culture-confirmed for non-pneumophila species.14
Asymptomatic patients An additional 11 cases were confirmed as non-pneumophila species by PCR, but not by culture. Notably, in 2020 Danish epidemiologists
also found 18 patients that returned positive PCR results for non-pneumophila species, but were asymptomatic, and therefore were not considered to have Legionnaires’ disease. As stated in their
UAT – Urinary Antigen test, Lp – Legionella pneumophila, L. spp – Legionella spp, SG – Sero-Group
Figure 2: 2020 Legionnaires’ disease cases in Denmark by Diagnostic Method and Species (adapted from SS1, 202114
and SSI, 202115 ). Very few cases caused
by non-pneumophila species were detected in Denmark, which does not rely on the UAT for initial diagnosis.
report: “Legionella non-pneumophila species occur in the vast majority of water systems (up to 100%), and often in higher numbers than L. pneumophila. The vast majority of these species have a very low or no infectiousness in humans, but the fact that they are very common produces a risk of ‘false’ positive PCR results, particularly in patients who undergo upper airway sampling.”14 As the Danish data confirms, the
70 °C / 158 °F 60 °C /140 °F
49 °C / 120 °F
Legionella dies immediately
As temperature rises above the optimal range, growth slows, and above 60 °C, 90% of Legionella die within two minutes
Optimal growth range
25 °C / 77 °F 0 °C /32 °F
As temperature decreases below the optimal range, growth slows, then Legionella becomes dormant
UAT is not a significant source of bias in assessing the risk posed by different species of Legionella; L. pneumophila is the most clinically relevant species, and should be the focus of Legionella sampling and control in water safety programmes. The researchers also highlighted that non-pneumophila species are nearly ubiquitous in water systems, and generally do not cause a risk to patient safety. A management programme that aims to eliminate these pervasive red herrings could take a disproportionate amount of resources, and potentially distract from areas of high L pneumophila risk in facilities, while contributing little to patient safety.
Management of Legionella in water systems Microbiological testing apart, effective management of waterborne pathogens in water systems is crucial to safeguarding patients. The detection of waterborne pathogens such as Legionella in healthcare water systems is one aspect to the overall water safety programme. However, while a zero tolerance would be ideal, from the above clinical data, it is clear that the control of L. pneumophila is of primary importance for minimising disease transmission. Fundamentally, the vast majority of
Figure 3: Temperature effects on survival and growth of Legionella in laboratory conditions (adapted from ASHRAE guidance16 effective control measure for Legionella.
34 Health Estate Journal May 2022 ). Maintaining temperature can be an
Legionnaires’ disease cases in healthcare buildings occur due to the failure to control microbial growth in water systems. Design and commissioning are important aspects for microbial control, yet during the build stage many parts of the water systems are left stagnant following pressure testing, which results in water contamination prior to occupation.
2020 Legionnaires’ disease cases in Denmark by diagnostic method and species
UAT (Lp SG1) or other PCR
Presumptive L. spp Culture Confirmed L. spp PCR confirmed L. spp
L.pneumophila SG1–16
Cases by diagnostic method
PCR-diagnosed cases by species
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