The Presence of a Specific Genotype of Legionella pneumophila Serogroup 1 in a Hospital and Municipal Water Distribution System over a 12-year Period

Tap water as the source of a Legionnaires' disease outbreak spread to several residential buildings and one hospital, Finland, 2020 to 2021

In Finland, all microbiology laboratories notify Legionella findings and physicians notify Legionnaires' disease (LD) cases to the National Infectious Disease Register. All cases are interviewed, and water samples obtained from potential places of exposure. Legionella isolates from humans and water are compared by whole genome sequencing (WGS). In March 2021, Legionella pneumophila serogroup 1 (Lp 1) pneumonia cases increased in one Finnish city (120,000 inhabitants) where single LD cases are detected annually. We identified 12 LD cases, nine living in different residential buildings and three nosocomial, linked by identical human and/or water isolates. Three of these cases were from January 2020, October 2020 and February 2021 and identified retrospectively. Eleven were diagnosed by urinary antigen test, 10 by PCR and five by culture; age ranged between 52 and 85 years, and 10 had underlying diseases. Nine of 12 homes of LD cases and 15 of 26 water samples from the hospital were positive for Lp 1, with concentrations up to 640,000 cfu/L. Water samples from regional storage tanks were negative. Positivity in homes and the hospital suggested inadequate maintenance measures. Enhanced surveillance combined with WGS was crucial in detecting this unusual LD outbreak related to domestic and hospital water systems.

Differential Proteome Between Patient-Related and Non-related Environmental Isolates of Legionella pneumophila

Molecular epidemiologic studies of Legionella have shown different molecular types coexisting in the same environment, with only one having the ability to trigger an outbreak. We therefore studied the proteome of isolates of these different molecular types in search of the proteins responsible for infection. In this study, we performed a differential proteomic analysis between patient-related and non-patient-related environmental isolates using two-dimensional difference gel electrophoresis (2D-DIGE) combined with mass spectrometry. Sixty-three spots were observed as being different between the two groups; 31 spots were identified corresponding to 23 different proteins. Patient-related isolates overexpressed proteins associated with metabolism, with enzymes of the tricarboxylic acid cycle and the degradation pathways being the most abundant proteins identified. However, the largest group of non-patient-related proteins was associated with stress response. Furthermore, the MOMP protein was located in different spots depending on their patient-related or non-patient-related origin, suggesting different post-translational modifications. According to these results, different bacterial adaptation pathways are activated in stress conditions which influence their ability to produce infection.

Legionella Risk Management and Control in Potable Water Systems: Argument for the Abolishment of Routine Testing

Legionella is an opportunistic pathogen of public health significance. One of the main sources of Legionella is potable water systems. As a consequence of aging populations there is an increasing demographic considered at high risk for Legionellosis and, as such, a review of the guidelines is required. Worldwide, Legionella has been detected from many potable water sources, suggesting it is ubiquitous in this environment. Previous studies have identified the limitations of the current standard method for Legionella detection and the high possibility of it returning both false negative and false positive results. There is also huge variability in Legionella test results for the same water sample when conducted at different laboratories. However, many guidelines still recommend the testing of water systems. This commentary argues for the removal of routine Legionella monitoring from all water distribution guidelines. This procedure is financially consuming and false negatives may result in managers being over-confident with a system or a control mechanism. Instead, the presence of the pathogen should be assumed and focus spent on managing appropriate control measures and protecting high-risk population groups.

Current and emerging Legionella diagnostics for laboratory and outbreak investigations

Legionnaires' disease (LD) is an often severe and potentially fatal form of bacterial pneumonia caused by an extensive list of Legionella species. These ubiquitous freshwater and soil inhabitants cause human respiratory disease when amplified in man-made water or cooling systems and their aerosols expose a susceptible population. Treatment of sporadic cases and rapid control of LD outbreaks benefit from swift diagnosis in concert with discriminatory bacterial typing for immediate epidemiological responses. Traditional culture and serology were instrumental in describing disease incidence early in its history; currently, diagnosis of LD relies almost solely on the urinary antigen test, which captures only the dominant species and serogroup, Legionella pneumophila serogroup 1 (Lp1). This has created a diagnostic "blind spot" for LD caused by non-Lp1 strains. This review focuses on historic, current, and emerging technologies that hold promise for increasing LD diagnostic efficiency and detection rates as part of a coherent testing regimen. The importance of cooperation between epidemiologists and laboratorians for a rapid outbreak response is also illustrated in field investigations conducted by the CDC with state and local authorities. Finally, challenges facing health care professionals, building managers, and the public health community in combating LD are highlighted, and potential solutions are discussed.

Legionnaires' disease from a cooling tower in a community outbreak in Lidköping, Sweden- epidemiological, environmental and microbiological investigation supported by meteorological modelling

Background

An outbreak of Legionnaires’ Disease took place in the Swedish town Lidköping on Lake Vänern in August 2004 and the number of pneumonia cases at the local hospital increased markedly. As soon as the first patients were diagnosed, health care providers were informed and an outbreak investigation was launched.

Methods

Classical epidemiological investigation, diagnostic tests, environmental analyses, epidemiological typing and meteorological methods.

Results

Thirty-two cases were found. The median age was 62 years (range 36 – 88) and 22 (69%) were males. No common indoor exposure was found. Legionella pneumophila serogroup 1 was found at two industries, each with two cooling towers. In one cooling tower exceptionally high concentrations, 1.2 × 10⁹ cfu/L, were found. Smaller amounts were also found in the other tower of the first industry and in one tower of the second plant. Sero- and genotyping of isolated L. pneumophila serogroup 1 from three patients and epidemiologically suspected environmental strains supported the cooling tower with the high concentration as the source. In all, two L. pneumophila strains were isolated from three culture confirmed cases and both these strains were detected in the cooling tower, but one strain in another cooling tower as well. Meteorological modelling demonstrated probable spread from the most suspected cooling tower towards the town centre and the precise location of four cases that were stray visitors to Lidköping.

Conclusions

Classical epidemiological, environmental and microbiological investigation of an LD outbreak can be supported by meteorological modelling methods.

The broad competence and cooperation capabilities in the investigation team from different authorities were of paramount importance in stopping this outbreak.

Longitudinal evaluation of the efficacy of heat treatment procedures against Legionella spp. in hospital water systems by using a flow cytometric assay

Legionella spp. are frequently isolated in hospital water systems. Heat shock (30 min at 70°C) is recommended by the World Health Organization to control its multiplication. The aim of the study was to evaluate retrospectively the efficacy of heat treatments by using a flow cytometry assay (FCA) able to identify viable but nonculturable (VBNC) cells. The study included Legionella strains (L. pneumophila [3 clusters] and L. anisa [1 cluster]) isolated from four hot water circuits of different hospital buildings in Saint-Etienne, France, during a 20-year prospective surveillance. The strains recovered from the different circuits were not epidemiologically related, but the strains isolated within a same circuit over time exhibited an identical genotypic profile. After an in vitro treatment of 30 min at 70°C, the mean percentage of viable cells and VBNC cells varied from 4.6% to 71.7%. The in vitro differences in heat sensitivity were in agreement with the observed efficacy of preventive and corrective heating measures used to control water contamination. These results suggest that Legionella strains can become heat resistant after heating treatments for a long time and that flow cytometry could be helpful to check the efficacy of heat treatments on Legionella spp. and to optimize the decontamination processes applied to water systems for the control of Legionella proliferation.

Nosocomial Legionnaires' disease caused by Legionella pneumophila serogroup 6: Implication of the sequence-based typing method (SBT)

Sequence-based typing (SBT) was used to determine the allelic profiles of 3 sporadic clinical isolates as well as 7 environmental isolates of Legionella pneumophila serogroup 6, isolated at the Karolinska Hospital during 2004. The clinical isolates were cultured from patients with nosocomial Legionnaires' disease (LD), while the environmental isolates were cultured from potable water sources of the hospital wards in the close vicinity of the 3 patients being investigated. The genes sequenced for the construction of the SBT profile included flaA, pilE, asd, mip, mompS and proA, in this pre-determined order and the allelic profile of the 10 isolates was identical (3, 13, 1, 28, 14, 9). Furthermore, 2 of the isolates, 1 clinical and 1 environmental, were analysed using the amplified fragment length polymorphism analysis (AFLP). The AFLP genotype of both isolates was congruent. Eight of 9 control L. pneumophila serogroup 6 isolates had the same SBT profile as the study isolates. We conclude that the environmental strain isolated from our hospital's drinking water is indistinguishable genotypically from the 3 clinical isolates of Legionella. However, this genotype of L. pneumophila is geographically widespread. Thus, results of genotyping must be evaluated in conjunction with the clinical and epidemiological data.

Genetic diversity of Legionella pneumophila in hospital water systems

It has been shown that different patients who had acquired legionellosis in a hospital setting were infected with the same strain even years apart. However, there are no longitudinal data describing the molecular epidemiology of Legionella pneumophila strains that contaminate a water system. This raised the question if there are any shifts of L. pneumophila strains over time, or after carrying out control measures. Using genotyping on a large collection of isolates, we investigated in a retrospective study the distribution of L. pneumophila serogroups and PFGE types in six different hospitals of the University of Heidelberg between 1991 and 2001. A total of 2012 water samples were drawn for routine testing and for evaluation of control measures, 747 samples were positive for L. pneumophila. Serogroups were determined by latex agglutination or by direct fluorescence assay; and 515 L. pneumophila isolates from water systems and six from patients underwent PFGE typing after SfiI-restriction. We identified seven serogroups and 19 genotypes among the water isolates. Each hospital had one to four predominating PFGE types that were stable over the investigation period. The oldest buildings in hospitals 4 and 5 (built 1876 and 1907) had more types than the newest one (built 1986). In all hospitals PFGE types were identified that could be found only sporadically. Although each hospital had its own warm water supply, we identified types that could be found in more than one hospital. However, there was no overlap of types in buildings that were fed from different wells. Infrequently occurring nosocomial legionellosis (n=3) were only caused by predominant strains. Contamination of water supplies seemed to be dominated by stable genotypes, even after various control measures. Additional genotypes could be isolated sporadically, however, their pathogenetic relevance seemed to be questionable.

Persistence of Legionella in hospital water supplies and nosocomial Legionnaires' disease

The molecular epidemiology of clinical and environmental Legionella species isolates was studied in seven hospitals from 1989 to 2006. The number of environmental pulsed field gel electrophoresis (PFGE) patterns ranged from one to nine according to the hospital. Genomic PFGE pattern persistence was observed in 71% of the hospitals, even after 17 years in some hospitals, and the relationship between environmental and clinical isolates was established. The isolates associated with hospital-acquired Legionnaires' disease corresponded to the persistent environmental PFGE patterns of Legionella pneumophila in potable water supplies.