Travel-associated Legionnaires’ disease: would changing cluster definition lead to the prevention of a larger number of cases?

Abstract

According to European Guidelines for Legionnaires’ Disease prevention and control, travel-associated Legionnaires’ disease (TALD) cases are managed differently if classified as sporadic or as part of a cluster and more stringent control measures are deployed after clusters are identified. In this study, we propose to modify the current cluster definition: ‘two or more cases of Legionnaires’ disease (LD) who stayed at, or visited, the same commercial accommodation site 2–10 days before onset of illness and whose onset is within the same 2-year period’ with a new cluster definition, i.e. accommodation sites associated with multiple cases regardless of the time elapsed between them. TALD cases occurred in Italy and in the Balearic Islands between 2005 and 2015 were analysed applying the current European Legionnaires’ Disease Surveillance Network (ELDSNet) cluster definition. In a sample of selected accommodation sites with multiple cases, a microbiological study was also conducted. Using the new definition, 63 additional sites (16.4% increase) and 225 additional linked cases (19.5% increase) were identified. Legionella pneumophila sg1 was isolated from 90.7% of the selected accommodation sites. The use of the here proposed TALD cluster definition would warrant a full investigation for each new identified case. This approach should therefore increase the number of sites that will require a risk assessment and, in the presence of an increased risk, the adoption of LD control measures to hopefully prevent additional cases.

Epidemiological analysis of Legionnaires' disease in Scotland: a genomic study

“…10 The broad timeframe of up to 17 years for isolates within many clusters supports a recent proposal to re-evaluate the European Legionnaires' Disease Surveillance Network cluster definition to consider accommodation sites associated with multiple cases regardless of the time elapsed between them. 34 To support this proposal, we advocate the importance of ongoing environmental surveillance for L pneumophila in industrial and public water systems to support the rapid delineation of Legionnaires' disease clinical cases and outbreaks. Taken together, our findings support the proposal that routine regular environmental sampling is required to facilitate the WGS-based identification of epidemiological links and the attribution of outbreak sources, and to inform public health measures targeting endemic clones that are an ongoing threat to public health.…”

Overview of the Clinical and Molecular Features of Legionella Pneumophila: Focus on Novel Surveillance and Diagnostic Strategies

“…Noteworthy, the incidence of legionellosis in Italy has increased over the years, reaching 52.9 cases per million inhabitants in 2019, which shows a slight increase compared to the previous year (48.9/1,000,000) [13].…”

“…A year later, Legionella pneumophilia (LP) was recognized as the etiologic agent of Legionnaires' disease (LD) [3]. Currently, 15 different serogroups of LP were recognized of which serogroup 1 is the most clinically relevant accounting for 80-90% of Legionnaires' disease cases, while other serogroups (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) are less common and occasionally cause legionellosis.…”

Characterization of a Novel Species of Legionella Isolated from a Healthcare Facility: Legionella resiliens sp. nov

“…From a natural or artificial environment, it can spread via aerosol, infecting human beings. The inhalation of the contaminated aerosol may result in Legionnaires' disease (LD) or Pontiac Fever [1,10,11]. Considering that all Legionellae are able to grow intracellularly in host cells, it is assumed that several species can cause disease in humans, when some conditions occur: immunocompromised patients, smokers, elderly people, etc.…”