Results of intensified source finding efforts among community-acquired cases of Legionnaires’ disease – first results of the German LeTriWa study; Berlin, 2016−2019

AbstractIntroductionSources of infection of most cases of community-acquired Legionnaires’ disease (CALD) are unknown.ObjectiveIdentification of sources of infection of CALD.SettingBerlin; December 2016–May 2019.ParticipantsAdult cases of CALD reported to district health authorities and consenting to the study; age and hospital matched controls.Main outcome measurePercentage of cases of CALD with identified source of infection.MethodsAnalysis of secondary patient samples for monoclonal antibody (MAb) type (and sequence type); questionnaire-based interviews, analysis of standard household water samples for Legionella concentration followed by MAb (and sequence) typing of Legionella pneumophila serogroup 1 (Lp1) isolates; among cases taking of additional water samples to identify the infectious source as appropriate; recruitment of control persons for comparison of exposure history and contents of standard household water samples. For each case an appraisal matrix was filled in to attribute any of three source types (external (non-residence) source, residential non-drinking water (RnDW) source, residential drinking water (RDW) as source) using three evidence types (microbiological results, cluster evidence, analytical-comparative evidence (using added information from controls)).ResultsInclusion of 111 study cases and 202 controls. Median age of cases was 67 years (range 25– 93 years), 74 (67 %) were male. Among 65 patients with urine typable for MAb type we found a MAb 3/1-positive strain in all of them.Compared to controls being a case was not associated with a higher Legionella concentration in standard household water samples, however, the presence of a MAb 3/1-positive strain was significantly associated (OR = 4.9, 95 % confidence interval (CI) 1.7 to 11). Thus, a source was attributed by microbiological evidence if it contained a MAb 3/1-positive strain, by cluster evidence if at least two cases were exposed to it and by analytical-comparative evidence if a case was exposed to it and the type of source was statistically significantly associated with being a case. We identified an infectious source in 53 (48 %) of 111 cases: in 16 (14 %) an external source, in 9 (8 %) a RnDW source, and in 28 (25 %) we attributed RDW. We attributed 9 cases to RnDW because cases were associated with wearing not regularly disinfected dentures (OR = 3.2, 95 % CI 1.3 to 7.8).ConclusionUsing the appraisal matrix we attributed almost half of all cases of CALD to an infectious source, predominantly RDW. Risk for LD seems to be conferred primarily by the type of Legionella rather than the amount. Dentures as a new infectious source needs further, in particular, integrated microbiological, molecular and epidemiological confirmation.