Air-conditioner cooling towers as complex reservoirs and continuous source of Legionella pneumophila infection evidenced by a genomic analysis study in 2017, Switzerland.

IntroductionWater supply and air-conditioner cooling towers (ACCT) are potential sources of Legionella pneumophila infection in people. During outbreaks, traditional typing methods cannot sufficiently segregate L. pneumophila strains to reliably trace back transmissions to these artificial water systems. Moreover, because multiple L. pneumophila strains may be present within these systems, methods to adequately distinguish strains are needed. Whole genome sequencing (WGS) and core genome multilocus sequence typing (cgMLST), with their higher resolution are helpful in this respect. In summer 2017, the health administration of the city of Basel detected an increase of L. pneumophila infections compared with previous months, signalling an outbreak.AimWe aimed to identify L. pneumophila strains populating suspected environmental sources of the outbreak, and to assess the relations between these strains and clinical outbreak strains.MethodsAn epidemiological and WGS-based microbiological investigation was performed, involving isolates from the local water supply and two ACCTs (n = 60), clinical outbreak and non-outbreak related isolates from 2017 (n = 8) and historic isolates from 2003-2016 (n = 26).ResultsIn both ACCTs, multiple strains were found. Phylogenetic analysis of the ACCT isolates showed a diversity of a few hundred allelic differences in cgMLST. Furthermore, two isolates from one ACCT showed no allelic differences to three clinical isolates from 2017. Five clinical isolates collected in the Basel area in the last decade were also identical in cgMLST to recent isolates from the two ACCTs.ConclusionCurrent outbreak-related and historic isolates were linked to ACCTs, which form a complex environmental habitat where strains are conserved over years.

Changes in the epidemiology of pneumococcal bacteremia in a Swiss university hospital during a 15-year period, 1986-2000.

OBJECTIVE: To evaluate changes in epidemiological characteristics and outcome of patients with pneumococcal bacteremia during a 15-year period in a Swiss university hospital. PATIENTS AND METHODS: We reviewed the medical records of all hospitalized adults at the University Hospital Basel, Basel, Switzerland, whose blood culture yielded Streptococcus pneumoniae from January 1, 1986, through December 31, 2000. RESULTS: We analyzed 405 episodes of pneumococcal bacteremia in 394 patients. The mean annual incidence of 1.78 episodes per 1000 hospital admissions was inversely related to the mean atmospheric temperature of the area. During the study period, penicillin nonsusceptibility increased from 0% to 17%. The overall case-fatality rate was 25%, which decreased from 33% to 17% between the first and the second half of the study period (P<.001). The proportion of women with pneumococcal bacteremia increased from 37% to 52%. Independent risk factors for fatal outcome were coronary artery disease (P<.001; relative risk [RR], 4.3; 95% confidence interval [CI], 3.4-5.1), neutropenia (P=.001; RR, 3.2; 95% CI, 1.9-4.8), and age 65 years or older (P=.001; RR, 2.9; 95% CI, 1.8-4.2), whereas prior respiratory tract infection (P=.03; RR, 0.3; 95% CI, 0.1-0.5) and the occurrence of pneumococcal bacteremia in the second half of the study period (P=.01; RR, 0.4; 95% CI, 0.2-0.6) were independent predictors of survival. The case-fatality rate in human immunodeficiency virus (HIV)-infected patients was significantly lower than in patients not infected with HIV or in those with unknown HIV status (9% vs 27%; P=.006), which correlated with the younger mean +/- SD age of HIV-infected patients (33.2+/-6.6 years) compared with patients not infected with HIV (63.1+/-18.1 years) (P<.001). CONCLUSIONS: The case-fatality rate of patients with pneumococcal bacteremia decreased significantly between the first and second half of the study period, despite the increased prevalence of penicillin-nonsusceptible isolates. Independent risk factors for fatal outcome were coronary artery disease, neutropenia, and age 65 years or older, whereas prior respiratory tract infection and the occurrence of pneumococcal bacteremia in the second half of the study period were independent predictors of survival. HIV infection was a predisposing factor for pneumococcal bacteremia but was not a risk factor for fatal outcome.