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

A Nicolau,M L Ricci,V Drasar,M Scaturro,M G Caporali,M C Rota,A Bella,M Gumá,S Crespi

doi:10.1017/s0950268818003266

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.

Highlights

In 1987, the European Surveillance Scheme for travel-associated Legionnaires’ disease (TALD), later called EWGLINET, was firstly introduced [1] and since April 2010, the scheme is called European Legionnaires’ Disease Surveillance Network (ELDSNet) and it is coordinated by the European Centre for Disease Prevention and Control (ECDC) based in Stockholm, Sweden [2].Legionnaires’ disease (LD) cluster definition changed over time
Until 2001, a cluster of TALD was defined as two or more LD cases who stayed at the same accommodation site during the incubation period and whose onset was within a 6-month period, while cases occurring at sites with previous cases more than 6 months earlier were categorised as ‘linked’
Once a case is reported to the ECDC database TESSy, accommodation details are checked in order to identify possible previously reported TALD cases associated with the same accommodation site

Summary

Introduction

In 1987, the European Surveillance Scheme for travel-associated Legionnaires’ disease (TALD), later called EWGLINET, was firstly introduced [1] and since April 2010, the scheme is called European Legionnaires’ Disease Surveillance Network (ELDSNet) and it is coordinated by the European Centre for Disease Prevention and Control (ECDC) based in Stockholm, Sweden [2].Legionnaires’ disease (LD) cluster definition changed over time. According to the new definition, a cluster was defined as two or more cases of LD who stayed at or visited the same commercial accommodation site in the 2–10 days before onset of illness and whose onset was within the same 2-year period. This change in the definition of clusters brought to a rise in the number of clusters detected from 28 in 2000 to 72 in 2001, of which 43 (60%) would have met the old cluster definition, with a gain of 29 extra clusters. Many of the linked cases that the previous definition would have identified were absorbed into these ‘new’ clusters [4]

Methods

Results

Conclusion