The burden of legionnaires’ disease in Belgium, 2013 to 2017

Abstract

Background Legionnaires’ disease (LD) is a severe bacterial infection causing pneumonia. Surveillance commonly underestimates the true incidence as not all cases are laboratory confirmed and reported to public health authorities. The aim of this study was to present indicators for the impact of LD in Belgium between 2013 and 2017 and to estimate its true burden in the Belgian population in 2017, the most recent year for which the necessary data were available. Methods Belgian hospital discharge data, data from three infectious disease surveillance systems (mandatory notification, sentinel laboratories and the national reference center), information on reimbursed diagnostic tests from the Belgian National Institute for Health and Disability Insurance and mortality data from the Belgian statistical office were used. To arrive at an estimate of the total number of symptomatic cases in Belgium, we defined a surveillance pyramid and estimated a multiplication factor to account for LD cases not captured by surveillance. The multiplication factor was then applied to the pooled number of LD cases reported by the three surveillance systems. This estimate was the basis for our hazard- and incidence-based Disability-Adjusted Life Years (DALYs) calculation. To account for uncertainty in the estimations of the DALYs and the true incidence, we used Monte Carlo simulations with 10,000 iterations. Results We found an average of 184 LD cases reported by Belgian hospitals annually (2013–2017), the majority of which were male (72%). The surveillance databases reported 215 LD cases per year on average, 11% of which were fatal within 90 days after diagnosis. The estimation of the true incidence in the community yielded 2674 (95% Uncertainty Interval [UI]: 2425–2965) cases in 2017. LD caused 3.05 DALYs per case (95%UI: 1.67–4.65) and 8147 (95%UI: 4453–12,426) total DALYs in Belgium in 2017, which corresponds to 71.96 (95%UI: 39.33–109.75) DALYs per 100,000 persons. Conclusions This analysis revealed a considerable burden of LD in Belgium that is vastly underestimated by surveillance data. Comparison with other European DALY estimates underlines the impact of the used data sources and methodological approaches on burden estimates, illustrating that national burden of disease studies remain essential.

Epidemiology of Legionnaires’ Disease in Italy, 2004–2019: A Summary of Available Evidence

“…To date, this upsurge is a common and not well-understood feature of nearly all high-income countries. Several explanations have been proposed [3,8,20,34,35], but none of them is either satisfying nor explicative [2,3,9,10,38]. In fact, we are unable to rule out that this increase in case numbers could be nothing more than an artifact.…”

“…), is to date either difficult or substantially biased from its roots [50,62]. Eventually, it must be stressed that our estimates only included LD, while the occurrence of PF was not ascertained as it is not included in the current case definition for LD by the European Union [38].…”

“…As a consequence, not only do we lack significant data about the demographics of LD cases, with resulting uncertainties in eventual estimates, but significant information about the reported signs and symptoms were not available to our analysis. This is particularly interesting, as an accurate analysis of clinical features of reported cases may either confirm or dismiss the hypothesis that the upsurge of LD cases should be more properly retained as an intensification of testing for Legionella [2,3,25,38,62]. Second, National Bulletins obviously included reported cases, but both previous remarks and the significant heterogeneity in incidence estimates hint for an inconsistent and often inappropriate notification of incident cases to the competent health authorities [8,27,39,40].…”

“…More precisely, the pooled incidence rate has increased 4.5 times since 2003, with an AIR climbing from 1.053 per 100,000 in 2003 (95% CI 0.869 to 1.237) to 4.669 per 100,000 (95% CI 4.251 to 5.088) in 2019. In fact, during the last decade, not only has Italy consistently reported the highest raw number of LD in all of western Europe, but the incidence rates have increased over time, being second only to Slovenian figures (i.e., 5.1 per 100,000 in 2015; 4.5 per 100,000 in 2016; 5.7 per 100,000 in 2017; 7.7 per 100,000 in 2018; 9.4 per 100,000 in 2019) [20,[34][35][36]38]. Notably, when Italian AIRs were compared to available EU-EEA estimates for 2005-2019, the corresponding ratio regularly increased from 1.1 in 2005 to 2.4 in 2019 (average of 1.8 for the whole timeframe, but 1.5 for 2005-2011 and 2.1 for 2012-2019).…”

“…Last but not least, hotels may host a large number of visitors, who might be exposed to the same source during their stay, with resulting clusters and even outbreaks [30,53,59]. As a consequence, specifically targeted interventions have been promoted not only at the Italian level, but more broadly at the European level, including the implementation of an integrated surveillance network in all EU-EEA countries [30,34,38]. Not coincidentally, even though the number of national and international tourists and tourism-related facilities has more than doubled during the last decade (according to the estimates of ISTAT, the number of international travelers in Italy skyrocketed from 165 million in 2010 to nearly 400 million in 2019), the raw number of notified cases between 2004-2011 and 2012-2019 exhibited a far more limited increase, from 2024 to 2943, with a substantial decrease for the proportion of TALD on the total of LD (i.e., 25.6 to 18.8%).…”