A Cluster of Legionnaires' Disease in Belgium Linked to a Cooling Tower
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Epidemiology and Infection A cluster of Legionnaires’ disease in Belgium linked to a cooling tower, August–September cambridge.org/hyg 2016: practical approach and challenges 1 1 2 3 1 1 Original Paper N. Hammami , V. Laisnez , I. Wybo , D. Uvijn , C. Broucke , A. Van Damme , L. Van Zandweghe4, W. Bultynck4, W. Temmerman4, L. Van De Ginste4, T. Moens3 Cite this article: Hammami N et al (2019). A 5,6 cluster of Legionnaires’ disease in Belgium and E. Robesyn linked to a cooling tower, August–September 2016: practical approach and challenges. 1Agency for Care and Health, Infection Prevention and Control, Flemish Community, Ghent, Belgium; 2Department – Epidemiology and Infection 147, e326, 1 7. of Microbiology and Infection Control, National Reference Centre for Legionella Pneumophila, Universitair https://doi.org/10.1017/S0950268819001821 Ziekenhuis Brussel, Vrije Universiteit Brussel, Brussels, Belgium; 3Agency for Care and Health, Environmental Health, Flemish Community, Ghent, Belgium; 4Pneumology Department, Sint-Blasius Hospital, Dendermonde, Received: 26 June 2019 5 Revised: 2 October 2019 Belgium; European Centre for Disease Prevention and Control, Surveillance and Response Support Unit, 6 Accepted: 3 October 2019 Stockholm, Sweden and Department of Global Public Health, Karolinska Institutet, Stockholm, Sweden Key words: Abstract Community outbreaks; geographical information systems; Legionnaires’ disease A cluster of Legionnaires’ disease (LD) with 10 confirmed, three probable and four possible cases occurred in August and September 2016 in Dendermonde, Belgium. The incidence in Author for correspondence: E. Robesyn, E-mail: Emmanuel.Robesyn@ecdc. the district was 7 cases/100 000 population, exceeding the maximum annual incidence in europa.eu the previous 5 years of 1.5/100 000. Epidemiological, environmental and geographical inves- tigations identified a cooling tower (CT) as the most likely source. The case risk around the tower decreased with increasing distance and was highest within 5 km. Legionella pneumo- phila serogroup 1, ST48, was identified in a human respiratory sample but could not be matched with the environmental results. Public health authorities imposed measures to con- trol the contamination of the CT and organised follow-up sampling. We identified obstacles encountered during the cluster investigation and formulated recommendations for improved LD cluster management, including faster coordination of teams through the outbreak control team, improved communication about clinical and environmental sample analysis, more detailed documentation of potential exposures obtained through the case questionnaire and earlier use of a geographical information tool to compare potential sources and for hypothesis generation. Introduction Legionnaires’ disease (LD) is pneumonia caused by Legionella spp. and is often severe [1]. Early diagnosis and appropriate treatment are important to improve the clinical outcome. Infection occurs by inhalation of aerosolised contaminated water particles. Aerosol-generating devices such as cooling towers (CTs), spa-pools, showers and fountains can infect people indoor or outdoor, and can cause outbreaks [2–7]. LD is a notifiable infection in Belgium to allow for source identification and adequate con- trol measures to prevent new infections [1, 8, 9]. In 2015, Belgium reported 165 cases of LD to the European Centre of Disease Prevention and Control (ECDC) [10], a national notification rate of 1.47/100 000. In this paper, we describe a cluster of LD in Dendermonde, a district in Belgium, with a population of 198 494 [11]. On 9th September 2016, a third case of LD within 2 weeks was notified to the public health authorities. This led to case investigations and active case finding. A total of 10 confirmed, three probable and four possible LD cases with onset of disease between 20th August and 12th September 2016 were detected. We used the ECDC outbreak investigation toolkit and the geographical information tool for identification of potential © European Centre for Disease Prevention and Control 2019. This is an Open Access article, sources [12, 13]. We also formulated recommendations for future outbreak investigations. distributed under the terms of the Creative Commons Attribution licence (http:// creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and Methods reproduction in any medium, provided the original work is properly cited. Case definitions Case finding was done by contacting hospitals and primary care physicians. Cases had to have onset of symptoms from 1st August 2016 onwards and had to live or work in Dendermonde district in the 14 days before onset of symptoms. The clinical and laboratory criteria to define and classify cases were in line with the EU surveillance definitions [14]. Downloaded from https://www.cambridge.org/core. IP address: 170.106.35.229, on 03 Oct 2021 at 02:49:16, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268819001821 2 N. Hammami et al. Epidemiological investigations extract (glycine, vancomycin, polymyxin and cycloheximide) and BCYE [21]. The Legionella strains isolated after 7 days were The epidemiological investigations were performed by the sent to the NRC for matching with available human samples. Infection Control team of the Agency for Care and Health. The Sample results and Legionella management plans were assessed following clinical data were collected from each suspect case: during on-site visits by the Environmental Health team. No date of symptom onset and diagnosis, type and result of diagnos- monoclonal subtyping was performed on clinical or environmen- tic test, underlying disease or risk factors and recent admission to tal isolates. hospital. Each case was interviewed over phone, using a standar- dised questionnaire consistent with the ECDC trawling question- naire [12], to collect information about residence, profession and Use of outbreak investigation tools workplace, stays away from home (including history of travel or hospitalisation) and possible exposure to aerosol-generating Post-outbreak, we used the ECDC geographical information tool ’ devices during 14 days prior to symptom onset. Data entry was [13] to map cases residences and we visualised case density in done in Excel 2010®. The most likely exposure period under the Dendermonde district. scenario of a point source contamination was estimated by sub- Potential sources were also mapped in the tool, and the attack tracting the minimum and maximum incubation periods from rate per 100 000 population was estimated in concentric zones respectively the first and last dates of onset [15]. around each potential source by dividing the case count by the population in each concentric zone [13]. Relative risks were esti- mated with the risk outside the largest concentric zone but within Microbiological investigations the two bordering provinces as baseline. For the evaluation of the cluster investigation, we assessed A commercial urine antigen test (Alere BinaxNow®) was used to retrospectively the six aspects listed in the ECDC LD outbreak detect the Legionella pneumophila serogroup 1 soluble antigen investigation toolkit [12]: (1) summarising background informa- in all suspect cases. Blood and respiratory samples were sent to tion; (2) data collection and convening of a coordinating outbreak the National Reference Centre (NRC) for Legionella in Brussels control team; (3) data management and (4) data analysis to gen- for confirmation of diagnosis. Traditional culturing techniques erate a hypothesis of a common outbreak source; (5) support to on buffered charcoal yeast extract agar (BCYE) and Legionella public health decisions about control measures and (6) appropri- BMPA Selective Agar (Oxoid, UK), as well as real-time polymer- ate communication throughout the investigation. These aspects ase chain reaction (PCR) based on mip-gene were applied on are also reflected in the Flemish LD outbreak investigation respiratory samples [16, 17]. Identification of isolates was per- procedure. formed by matrix-assisted laser desorption-ionisation time of flight mass spectrometry using a Microflex LT mass spectrometer with MALDI Biotyper 3.1 software and Bruker Reference Library Results v5.0.0.0 (5989 MSP) (Bruker Daltonik GmbH, Bremen, Epidemiological investigations Germany). Serogroup typing (differentiation between serogroups 1 and 2–15) was performed by latex agglutination using a Upon the alert, clinicians in one hospital mentioned an increase Microgen Legionella latex kit (Microgen Bioproducts Ltd., UK). in admissions for pneumonia since 25th August. They identified The NRC performs sequence-based typing on clinical samples – mostly retrospectively – 23 suspect patients admitted in two with L. pneumophila serogroup 1 isolates for discrimination of hospitals, with date of onset between 20th August and 12th strains [18, 19]. September. The case definition for patients possibly belonging For the serological examination, an indirect immunofluores- to the community cluster was set on 12th September. Among cence test was used to detect L. pneumophila pooled serogroup the 17 retained (confirmed, probable or possible) cases, one was 1–6(L. pneumophila 1–6 IFA, Meridian, Villa Cortese, Italy). on immunosuppressive treatment, one suffered from chronic pul- The NRC does not distinguish serogroup 1 from the other ser- monary disease, one reported to be a smoker and four were over