Street Cleaning Trucks as Potential Sources of Legionella pneumophila

Association of Natural Waterways and Legionella pneumophila Infection in Eastern Wisconsin: A Case-Control Study

Preliminary research has suggested possible associations between natural waterways and Legionella infection, and we previously explored these associations in eastern Wisconsin using positive L. pneumophila serogroup 1 urine antigen tests (LUAT) as diagnostic. This case-control study was a secondary analysis of home address data from patients who underwent LUAT at a single eastern Wisconsin health system from 2013 to 2017. Only zip codes within the health system's catchment area that registered ≥3 positive cases and ≥50 completed tests, as well as geographically adjacent zip codes with ≥2 positive cases and ≥50 tests, were included. A 1:3 ratio of cases to randomly selected controls was used. Home addresses were geocoded and mapped using ArcGIS software (Esri); nearest waterway and distance to home was identified. Distance to nearest waterway according to ArcGIS was verified/corrected using Google Maps incognito. Distances were analyzed using chi-squared and 2-sample t-tests. Overall, mean distance to nearest waterway did not differ between cases (2958 ± 2049 ft) and controls (2856 ± 2018 ft; P=0.701). However, in a subset of nonurban zip codes, cases were closer to nearest waterway than controls (1165 ± 905 ft vs 2113 ± 1710 ft; P=0.019). No association was found between cases and type of waterway. Further research is needed to investigate associations and differences between natural and built environmental water sources in relation to legionellosis.

A Community Outbreak of Legionnaires' Disease with Two Strains of L. pneumophila Serogroup 1 Linked to an Aquatic Therapy Centre

An outbreak of Legionnaires' disease affected 18 people in Montpellier, a town of the south of France, between December 2016 and July 2017. All cases were diagnosed by a positive urinary antigen test. No deaths were reported. Epidemiological, environmental and genomic investigations (nested Sequence-Based Typing (nSBT) and whole genome sequencing) were undertaken. For the cases for which we had information, four had a new isolate (ST2471), one had a different new isolate (ST2470), one had a genomic pattern compatible with the ST2471 identified by nSBT (flaA = 3), and one had a genomic pattern not compatible with two previous identified STs (pilE = 6). The analysis conducted on the pool of an aquatic therapy center revealed seven isolates of Legionella pneumophila. Whole genome analysis confirmed the link between the environmental and clinical isolates for both ST2470 and ST2471. As the outbreak occurred slowly, with several weeks between new cases, it was not possible to immediately identify a common source. The sixth case was the first to report having aquatic therapy care. Of the 18 cases, eight had attended the aquatic therapy center and the other 10 were inhabitants who lived, worked or walked close to the center. The main cause for this outbreak was the lack of facility maintenance. This investigation highlights the risk to public health of aquatic therapy centers for users and nearby populations, and emphasizes the need for risk reduction measures with specific guidelines to improve health and safety in aquatic facilities.

Epidemiologic Survey of Legionella Urine Antigen Testing Within a Large Wisconsin-Based Health Care System

Purpose

Legionella pneumophila pneumonia is a life-threatening, environmentally acquired infection identifiable via Legionella urine antigen tests (LUAT). We aimed to identify cumulative incidence, demographic distribution, and undetected disease outbreaks of Legionella pneumonia via positive LUAT in a single eastern Wisconsin health system, with a focus on urban Milwaukee County.

Methods

A multilevel descriptive ecologic study was conducted utilizing electronic medical record data from a large integrated health care system of patients who underwent LUAT from 2013 to 2017. A random sample inclusive of all positive tests was reviewed to investigate geodemographic differences among patients testing positive versus negative. Statistical comparisons used chi-squared or 2-sample t-tests; stepwise regression followed by binary logistic regression was used for multivariable analysis. Positive cases identified by LUAT were mapped to locate hotspots; positive cases versus total tests performed also were mapped by zip code.

Results

Of all LUAT performed (n=21,599), 0.68% were positive. Among those in the random sample (n=11,652), positive cases by LUAT were more prevalent in the June-November time period (86.2%) and younger patients (59.4 vs 67.7 years) and were disproportionately male (70.3% vs 29.7%) (P<0.0001 for each). Cumulative incidence was higher among nonwhite race/ethnicity (1.91% vs 1.01%, P<0.0001) but did not remain significant on multivariable analysis. Overall, 5507 tests were performed in Milwaukee County zip codes, yielding 82 positive cases by LUAT (60.7% of all positive cases in the random sample). A potential small 2016 outbreak was identified.

Conclusions

Cumulative incidence of a positive LUAT was less than 1%. LUAT testing, if done in real time by cooperative health systems, may complement public health detection of Legionella pneumonia outbreaks.

A valuable experimental setup to model exposure to Legionella's aerosols generated by shower-like systems

The mechanism underlying Legionella aerosolization and entry into the respiratory tract remains poorly documented. In previous studies, we characterized the aerodynamic behaviour of Legionella aerosols and assessed their regional deposition within the respiratory tract using a human-like anatomical model. The aim of this study was to assess whether this experimental setup could mimic the exposure to bioaerosols generated by showers. To achieve this objective we performed experiments to measure the mass median aerodynamic diameter (MMAD) as well as the emitted dose and the physiological state of the airborne bacteria generated by a shower and two nebulizers (vibrating-mesh and jet nebulizers). The MMADs of the dispersed bioaerosols were characterized using a 12-stage cascade low-pressure impactor. The amount of dispersed airborne bacteria from a shower was quantified using a Coriolis® Delta air sampler and compared to the airborne bacteria reaching the thoracic region in the experimental setup. The physiological state and concentration of airborne Legionella were assessed by qPCR for total cells, culture for viable and cultivable Legionella (VC), and flow cytometry for viable but non-cultivable Legionella (VBNC). In summary, the experimental setup developed appears to mimic the bioaerosol emission of a shower in terms of aerodynamic size distribution. Compared to the specific case of a shower used as a reference in this study, the experimental setup developed underestimates by 2 times (when the jet nebulizer is used) or overestimates by 43 times (when the vibrating-mesh nebulizer is used) the total emitted dose of airborne bacteria. To our knowledge, this report is the first showing that an experimental model mimics so closely an exposure to Legionella aerosols produced by showers to assess human lung deposition and infection in well-controlled and safe conditions.

Highlighting the Potency of Biosurfactants Produced by Pseudomonas Strains as Anti-Legionella Agents

Legionella pneumophila, the causative agent of Legionnaires' disease, is a waterborne bacterium mainly found in man-made water systems in close association with free-living amoebae and multispecies biofilms. Pseudomonas strains, originating from various environments including freshwater systems or isolated from hospitalized patients, were tested for their antagonistic activity towards L. pneumophila. A high amount of tested strains was thus found to be active. This antibacterial activity was correlated to the presence of tensioactive agents in culture supernatants. As Pseudomonas strains were known to produce biosurfactants, these compounds were specifically extracted and purified from active strains and further characterized using reverse-phase HPLC and mass spectrometry methods. Finally, all biosurfactants tested (lipopeptides and rhamnolipids) were found active and this activity was shown to be higher towards Legionella strains compared to various other bacteria. Therefore, described biosurfactants are potent anti-Legionella agents that could be used in the water treatment industry although tests are needed to evaluate how effective they would be under field conditions.