In September 2025, 50 laboratory-confirmed cases of Legionnaires’ disease (LD) were identified in Albertville, in south-eastern France. Initially, 23 patients were only clinically diagnosed and only confirmed later due to limited sensitivity of the urinary antigen screening test used. All cases occurred within 12 days, suggesting a common point source of massive contamination. Despite investigations and the rapid response of LD surveillance partners, the outbreak source has not yet been identified. Vigilance is maintained to detect possible new cases.

Between 1 November and 12 December 2019, a Legionnaires’ disease (LD) outbreak occurred in the Strasbourg metropolitan area, France. Epidemiological, environmental and genomic investigations (nested sequence-based typing and whole genome sequencing (WGS)) were undertaken to locate the outbreak source, characterise the causal Legionella strain, and understand its spread. Through a positive urinary antigen test, 28 cases (14 male; 14 female) with 70 years median age (range: 42–88 years) were diagnosed. Two died. For nine cases, typing revealed L. pneumophila serogroup 1 (Lp 1) sequence type (ST) 62 infection. Mapping where cases were during their incubation period pointed to a place south-west of Strasbourg city as the outbreak epicentre. There, in the biomass condensing boiler of a heating plant, high Lp 1 contamination levels (105–106 CFU/L) were discovered. Eight environmental Lp 1 isolates from inside the plant were ST62. Analysing WGS data from these isolates and the nine Lp 1 ST62 clinical isolates, found their sequences clustering with zero to two single nt polymorphisms. Sub-optimal maintenance and warm weather before the boiler started operating may have allowed Lp 1 proliferation within, with boiler fumes subsequently disseminating Lp 1, thereby exposing people. This outbreak highlights potential LD risks arising from innovative energy-saving heat production processes designed to reduce greenhouse gas emissions.

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.

OBJECTIVES:Implementation of an antibiotic resistance detection tool in Legionella daily surveillance at the French National Reference Centre for Legionella.METHODS:Systematic WGS of Legionella pneumophila isolates and bioinformatics detection of specific mutations linked to antibiotic resistance. Phenotypic validation of antibiotic resistance detected by WGS was performed by the broth microdilution method.RESULTS:More than 3000 L. pneumophila strains were screened for antibiotic resistance. A macrolide resistance-associated A2052G mutation in the 23S rRNA gene was identified in the genome of eight isolates from a hotel water network. High-level macrolide resistance (i.e. MICs of 1024-2048 mg/L for azithromycin and erythromycin) with no cross-resistance to other antimicrobials was phenotypically confirmed by antimicrobial susceptibility testing for the eight isolates.CONCLUSIONS:Systematic WGS of L. pneumophila is a powerful tool for first-line high-throughput screening of antibiotic resistance before phenotypic validation.

We describe a March 2020 co-occurrence of Legionnaires' disease (LD) and coronavirus disease in France. Severe acute respiratory syndrome coronavirus 2 co-infections were identified in 7 of 49 patients from LD case notifications. Most were elderly men with underlying conditions who had contracted severe pneumonia, illustrating the relevance of co-infection screening.

As countries in Europe gradually relaxed lockdown restrictions after the first wave, test–trace–isolate strategies became critical to maintain the incidence of coronavirus disease 2019 (COVID-19) at low levels1,2. Reviewing their shortcomings can provide elements to consider in light of the second wave that is currently underway in Europe. Here we estimate the rate of detection of symptomatic cases of COVID-19 in France after lockdown through the use of virological3 and participatory syndromic4 surveillance data coupled with mathematical transmission models calibrated to regional hospitalizations2. Our findings indicate that around 90,000 symptomatic infections, corresponding to 9 out 10 cases, were not ascertained by the surveillance system in the first 7 weeks after lockdown from 11 May to 28 June 2020, although the test positivity rate did not exceed the 5% recommendation of the World Health Organization (WHO)5. The median detection rate increased from 7% (95% confidence interval, 6–8%) to 38% (35–44%) over time, with large regional variations, owing to a strengthening of the system as well as a decrease in epidemic activity. According to participatory surveillance data, only 31% of individuals with COVID-19-like symptoms consulted a doctor in the study period. This suggests that large numbers of symptomatic cases of COVID-19 did not seek medical advice despite recommendations, as confirmed by serological studies6,7. Encouraging awareness and same-day healthcare-seeking behaviour of suspected cases of COVID-19 is critical to improve detection. However, the capacity of the system remained insufficient even at the low epidemic activity achieved after lockdown, and was predicted to deteriorate rapidly with increasing incidence of COVID-19 cases. Substantially more aggressive, targeted and efficient testing with easier access is required to act as a tool to control the COVID-19 pandemic. The testing strategy will be critical to enable partial lifting of the current restrictive measures in Europe and to avoid a third wave. Analyses of virological and surveillance data in France show that a substantial proportion of symptomatic cases of COVID-19 have remained undetected and that easily accessible and efficient testing is required to control the pandemic.

In the WHO European Region, COVID-19 surveillance was implemented 27 January 2020. We detail the first European cases. As at 21 February, nine European countries reported 47 cases. Among 38 cases studied, 21 were linked to two clusters in Germany and France, 14 were infected in China. Median case age was 42 years; 25 were male. Late detection of the clusters' index cases delayed isolation of further local cases. As at 5 March, there were 4,250 cases.

ABSTRACT A novel testing policy was implemented in May in France to systematically screen potential COVID-19 infections and suppress local outbreaks while lifting lockdown restrictions. 20,736 virologically-confirmed cases were reported in mainland France from May 13, 2020 (week 20, end of lockdown) to June 28 (week 26). Accounting for missing data and the delay from symptom onset to confirmation test, this corresponds to 7,258 [95% CI 7,160-7,336] cases with symptom onset during this period, a likely underestimation of the real number. Using age-stratified transmission models parameterized to behavioral data and calibrated to regional hospital admissions, we estimated that 69,115 [58,072-77,449] COVID-19 symptomatic cases occurred, suggesting that 9 out of 10 cases with symptoms were not ascertained. Median detection rate increased from 7% [6-9]% to 31% [28-35]% over time, with regional estimates varying from 11% (Grand Est) to 78% (Normandy) by the end of June. Healthcare-seeking behavior in COVID-19 suspect cases remained low (31%) throughout the period. Model projections for the incidence of symptomatic cases (4.5 [3.9-5.0] per 100,000) were compatible with estimates integrating participatory and virological surveillance data, assuming all suspect cases consulted. Encouraging healthcare-seeking behavior and awareness in suspect cases is critical to improve detection. Substantially more aggressive and efficient testing with easier access is required to act as a pandemic-fighting tool. These elements should be considered in light of the currently observed resurgence of cases in France and other European countries.

A novel coronavirus (severe acute respiratory syndrome coronavirus 2, SARS-CoV-2) causing a cluster of respiratory infections (coronavirus disease 2019, COVID-19) in Wuhan, China, was identified on 7 January 2020. The epidemic quickly disseminated from Wuhan and as at 12 February 2020, 45,179 cases have been confirmed in 25 countries, including 1,116 deaths. Strengthened surveillance was implemented in France on 10 January 2020 in order to identify imported cases early and prevent secondary transmission. Three categories of risk exposure and follow-up procedure were defined for contacts. Three cases of COVID-19 were confirmed on 24 January, the first cases in Europe. Contact tracing was immediately initiated. Five contacts were evaluated as at low risk of exposure and 18 at moderate/high risk. As at 12 February 2020, two cases have been discharged and the third one remains symptomatic with a persistent cough, and no secondary transmission has been identified. Effective collaboration between all parties involved in the surveillance and response to emerging threats is required to detect imported cases early and to implement adequate control measures.

We describe 2 cases of healthcare-associated Legionnaires’ disease in patients in France hospitalized 5 months apart in the same room. Whole-genome sequencing analyses showed that clinical isolates from the patients and isolates from the room’s toilet clustered together. Toilet contamination by Legionella pneumophila could lead to a risk for exposure through flushing.

The isolation of Legionella from respiratory samples is the gold standard for diagnosis of Legionnaires' disease (LD) and enables epidemiological studies and outbreak investigations. The purpose of this work was to adapt and to evaluate the performance of an amoebic coculture procedure (the amoeba plate test [APT]) for the recovery of Legionella strains from respiratory samples, in comparison with axenic culture and liquid-based amoebic coculture (LAC). Axenic culture, LAC, and APT were prospectively performed with 133 respiratory samples from patients with LD. The sensitivities and times to results for the three techniques were compared. Using the three techniques, Legionella strains were isolated in 46.6% (n = 62) of the 133 respiratory samples. The sensitivity of axenic culture was 42.9% (n = 57), that of LAC was 30.1% (n = 40), and that of APT was 36.1% (n = 48). Seven samples were positive by axenic culture only; for those samples, there were <10 colonies in total. Five samples, all sputum samples, were positive by an amoebic procedure only (5/5 samples by APT and 2/5 samples by LAC); all had overgrowth by oropharyngeal flora with axenic culture. The combination of axenic culture with APT yielded a maximal isolation rate (i.e., 46.6%). Overall, the APT significantly reduced the median time for Legionella identification to 4 days, compared with 7 days for LAC (P < 0.0001). The results of this study support the substitution of LAC by APT, which could be implemented as a second-line technique for culture-negative samples and samples with microbial overgrowth, especially sputum samples. The findings provide a logical basis for further studies in both clinical and environmental settings.

In France, approximately 1200 cases of Legionnaires disease (LD) are reported annually, and isolates are available for approximately 20% of cases identified since 2000. All Legionella pneumophila serogroup 1 (sg1) isolates are characterized by sequence-based typing at the National Reference Centre. LD cases caused by L. pneumophila sg1 reported from 2008 through 2012 were considered for the study. Our study objective was to describe cases according to their sequence type (ST). We also constructed multivariable modified Poisson regression models to estimate the incidence rate ratio (IRR) and to identify characteristics potentially associated with ST23 clones compared to ST1 and ST47 clones. We studied 1192 patients infected by ST1 (n = 109), ST23 (n = 236), ST47 (n = 123) or other STs (n = 724). The geographic distribution of the ST23 cases across the country was significantly different compared to other ST groups. This genotype was significantly associated with the absence of corticosteroid therapy compared to ST1 (IRR = 0.56; p 0.016). Concerning exposure, the ST23 genotype was significantly less associated with hospital-acquired infections compared to ST1 (IRR = 0.32; p 0.001), but it was more associated with infections acquired in hospitals and elderly settings compared with ST47. Finally, the ST23 genotype was less frequently associated with travel than other STs. Despite the large number of cases of ST23 infection, we did not identify any characteristics specific to this ST. However, we identified independent associations between ST1 and nosocomial transmission and steroid therapy. These findings should encourage further exploration, especially in terms of environmental diffusion, strain virulence and host factors.

The aim of this review was to describe the current knowledge of Legionnaires' disease (LD) illustrated by the epidemiological situation in France in 2013. LD is a severe pneumonia commonly caused by Legionella pneumophila serogroup 1. The diagnosis is usually based on the urinary antigen test. This rapid method reduces the delay between clinical suspicion and initiation of an appropriate treatment. However, the availability of a clinical strain is important to improve knowledge of circulating bacteria, to document case clusters, and to identify the sources of contamination. The source of contamination is unknown in most cases. The main contamination sources generating aerosols are water network systems and cooling towers. Thanks to the strengthening of clinical and environmental monitoring and to several guidelines, no epidemic has been reported in France since 2006. Despite these efforts, the number of LD cases has not decreased in recent years. It is essential that applied research continue to better understand the spatial and temporal dynamics of the disease and its characteristics (impact of environmental factors, sources of exposure, strains, host, etc.). Fundamental knowledge has been greatly improved (pathogenesis, immune mechanisms, etc.). The results of this research should help define new strategies for the diagnosis, prevention, and control to decrease the number of LD cases diagnosed every year.

In May 2013, Middle East Respiratory Syndrome Coronavirus (MERS-CoV) infection was diagnosed in an adult male in France with severe respiratory illness, who had travelled to the United Arab Emirates before symptom onset. Contact tracing identified a secondary case in a patient hospitalised in the same hospital room. No other cases of MERS-CoV infection were identified among the index case’s 123 contacts, nor among 39 contacts of the secondary case, during the 10-day follow-up period.

The notification rate of Legionnaires' disease (LD) in France was 2.4/100 000 population in 2010, varying across regions with an increasing rate from west to east. Two sources [mandatory notifications (MN) and a survey of hospital laboratories] were used in a capture-recapture study to estimate the number of LD cases and the sensitivity of the MN system at national and regional levels in 2010. The number of missed cases was estimated using Chapman's method. The estimated sensitivity of MN was 88.5% (95% CI 88.0-89.0) and ranged from 70% to 100% by region. The estimated incidence was 2.7/100 000 population. Sensitivity of the MN system improved since the previous capture-recapture estimates (10% in 1995, 33% in 1998). This study confirmed that the observed west-east gradient is not related to regional notification disparities. Ecological studies should be conducted to better understand the observed spatial variations in LD incidence.

The aims of this study were to describe the clinical, biological and radiological features of community-acquired (CA) Legionnaires’ disease (LD) and identify the predictors of mortality in hospitalised patients. Demographic data, risk factors, clinical and biological features, medical management, complications, and outcome from 540 hospitalised patients with confirmed CA LD were prospectively recorded. 8.1% of patients (44 out of 540) died. The predictors of survival after Kaplan–Meier analysis were male sex (p=0.01), age <60 yrs (p=0.02), general symptoms (p=0.006), intensive care unit (ICU) stay (p<0.001), and class II–III Pneumonia Severity Index score (p=0.004). Six predictors of death were identified by multivariate analysis: age (per 10-yr increment) (relative hazard (RH) 1.50, 95% CI 1.21–1.87), female sex (RH 2.00, 95% CI 1.08–3.69), ICU admission (RH 3.31, 95% CI 1.67–6.56), renal failure (RH 2.73, 95% CI 1.42–5.27), corticosteroid therapy (RH 2.54, 95% CI 1.04–6.20) and C-reactive protein (CRP) >500 mg·L−1 (RH 2.14, 95% CI 1.02–4.48). Appropriate antibiotic therapy was prescribed for 70.8% (292 out of 412) of patients after admission and for 99.8% (537 out of 538) of patients after diagnosis confirmation. In conclusion, female sex, age, ICU stay, renal failure, corticosteroid treatment and increased level of CRP are significant risk factors for mortality in CA LD.

We evaluated the contribution of amoebic coculture to the recovery of Legionella spp. from 379 respiratory samples. The sensitivity of axenic culture was 42.1%. The combination of axenic culture with amoebic coculture increased the Legionella isolation rate to 47.1%. Amoebic coculture was particularly efficient in isolating Legionella spp. from respiratory samples contaminated with oropharyngeal flora.

The clinical aspects and outcome of hospital (HA) and community-acquired (CA) cases of LD might be different. We explored these topics in 267 patients with LD hospitalized in France.