WATER HYGIENE AND SAFETY


Combating Legionella by focusing on the right species


Jimmy Walker PhD, BSc, a microbiologist with over 30 years’ experience in water microbiology and decontamination, discusses the important aspects of Legionnaires’ disease for those with responsibility for hospital water systems, and what we need to understand about the presence of this waterborne pathogen in such systems to safeguard patients.


Do Water Safety Groups (WSG) need to eliminate all species of Legionella from their water systems? The public health data indicates that focusing on Legionella pneumophila is the most effective way to reduce risks to patient safety. Data from Denmark demonstrate that the urinary antigen test is not a source of bias in public health figures, and that efforts to eliminate non-pneumophila species can be a red herring for WSGs, who should focus their efforts on managing the water system and on testing for L. pneumophila to minimise the risk to vulnerable patients.


Background Reducing Legionella risk to prevent Legionnaires’ disease is a key concern for Estates Departments and infection control specialists. WSGs must consider the risk posed by different Legionella species. The family Legionellaceae (commonly known as Legionella) comprises over 60 species, and more than 70 serogroups. Most healthcare and community-acquired Legionnaires’


2000 Number of cases 12-month moving average 1500 1000 500 0


Jan 2015


Jul 2015


Jan 2016


Jul 2016


Jan 2017


Jul 2017 Month


Source: European Centre for Disease Prevention and Control. Legionnaires’ disease. In ECDC Annual epidemiological report for 2019. Stockholm: ECDC, 2021.


Figure 1. Distribution of Legionnaires’ disease by month, EU/EAA, 2015-2019. The number of Legionnaires’ disease cases continues to increase despite current measures to prevent it.


Jan 2018


Jul 2018


Jan 2019


Jul 2019 ‘‘ To address


Legionnaires’ disease risks, we must


consider the type of species present, and the vulnerability of patients


disease cases (>95%) are caused by L. pneumophila, even though laboratories have consistently recovered non- pneumophila species from water systems, including healthcare settings.1,2 To address Legionnaires’ disease risks,


we must consider the type of species present, and the vulnerability of patients, and therefore Estates and Infection Control teams need to assess the public health data available on Legionnaires’ disease. Guidance published by the Health and Safety Executive broadly specifies Legionella monitoring. However, it is


not possible to recover all 60 species of Legionella using traditional culture-based methods, as is acknowledged in the ISO 11731 standard.3


Identifying the source of risk L. pneumophila is the greatest risk concern for patient safety. In England and Wales, non-pneumophila strains account for less than 1% of clinical cases.4


In France, 98%


of culture-confirmed Legionnaires’ disease cases are attributable to L. pneumophila.5 Similar statistics are seen in travel associated-Legionnaires’ disease cases,6 in Japan,7


and in US CDC outbreaks.8 An


analysis of 10 years of culture diagnoses from a study of more than 40,000 patients across the EU (including the UK) found that even for healthcare-acquired Legionnaires’ disease, 98% of the cases were caused by L. pneumophila.9


These


figures are consistent with recent scientific findings which begin to explain the mechanisms that increase the virulence of L. pneumophila when compared with other species.10


Improving the control of Legionella pneumophila


UK and ECDC clinical data demonstrate that we need to improve the control of Legionella pneumophila to prevent Legionnaires’ disease (Figure 1). Due to the clinical significance of L. pneumophila, and delays in diagnosis using culture, rapid urinary antigen tests (UAT) were developed for patient diagnosis, and detect L. pneumophila serogroup 1 antigen in urine samples from patients with symptoms of pneumonia.11


The


majority (90%) of the Legionnaires’ disease cases reported to the ECDC are initially diagnosed by the UAT.6 However, as the UAT only identifies cases associated with L. pneumophila serogroup 1, the question has been raised, ‘Is the true number of Legionnaires’ disease patients infected with non- pneumophila species under-reported, and, if so, what implications would that have for those responsible for Water Safety Plans?’


May 2022 Health Estate Journal 33


Number of cases


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