Legionella in drinking water: the detection method matters.

Legionella concentrations in drinking water have been regulated for decades and are evaluated with regard to their concentrations in drinking water plumbing systems (DWPS). The respective action levels differ at the international level. In Germany, the Federal Environment Agency (UBA) specifies the application of ISO 11731 for the detection of legionella in drinking water and gives a binding recommendation for the methods to be used for culturing and evaluation. Effective from 01 March 2019, the UBA recommendation was revised. The utilized culture media in the culture approach were altered, consequently affecting the spectrum of legionella colonies detected in drinking water. Using data from a routine legionella monitoring of a large laboratory, over a period of 6 years and 17,270 individual drinking water samples, allowed us to assess the impact of the alteration on the assessment of DWPS. By comparing the amount of action level exceedances before and after the method change, it could be demonstrated that exceedances are reported significantly more often under the new method. Consequently, the corresponding action level for evaluation of legionella contamination and the resulting risk to human health needs to be revised to avoid the misleading impression of increased health risk.

Comparison of the Legiolert™/Quanti-Tray® MPN test for the enumeration of Legionella pneumophila from potable water samples with the German regulatory requirements methods ISO 11731-2 and ISO 11731.

Due to the promising results of a previous study of the performance of the novel MPN method (Legiolert™/Quanti-Tray®) compared to ISO 11731-2, this study was performed to compare Legiolert for Legionella pneumophila with the German regulatory requirements methods ISO 11731-2 (100 ml membrane filtration) and ISO 11731 (1 ml direct plating) for the enumeration of L. pneumophila and Legionella spp. from potable water. Data from a multi-laboratory study according to ISO 17994 showed that Legiolert yielded on average higher counts of L. pneumophila than the ISO 11731-2 method, but the comparison with ISO 11731 was inconclusive due to the number of samples needing to be tested. Likewise, comparisons of the MPN method for 100 ml to the highest result of either ISO 11731 or ISO 11731-2 according to Federal Environmental Agency recommendation (2012) yielded no conclusive difference, regardless of whether non-pneumophila species of Legionella were included in the evaluation. The MPN method has a high specificity for L. pneumophila of 97.9% which compares favourably to the specificity of 95.3% quoted for ISO 11731. The new method represents a significant improvement in the enumeration of L. pneumophila from drinking water and related samples.

Rapid genotyping of Legionella pneumophila serogroup 1 strains by a novel DNA microarray-based assay during the outbreak investigation in Warstein, Germany 2013.

Between 1 August and 6 September 2013, an outbreak of Legionnaires' disease (LD) with 78 cases confirmed by positive urinary antigen tests occurred in Warstein, North Rhine-Westphalia, Germany. Legionella (L.) pneumophila, serogroup (Sg) 1, monoclonal antibody (mAb) subgroup Knoxville, sequence type (ST) 345, was identified as the epidemic strain. This strain was isolated from seven patients. To detect the source of the infection, epidemiological typing of clinical and environmental strains was performed in two consecutive steps. First, strains were typed by monoclonal antibodies. Indistinguishable strains were further subtyped by sequence-based typing (SBT) which is the internationally recognized standard method for epidemiological genotyping of L. pneumophila. In an early stage of the outbreak investigation, many environmental isolates were found to belong to the mAb subgroup Knoxville, but to two different STs, namely to ST 345, the epidemic strain, and to ST 600. A majority of environmental isolates belonged to ST 600 whereas the epidemic ST 345 strain was less common in environmental samples. To rapidly distinguish both Knoxville strains, we applied a novel typing method based on DNA-hybridization on glass chips. The new assay can easily and rapidly discriminate L. pneumophila Sg 1 strains. Thus, we were able to quickly identify the sources harboring the epidemic strain, i.e., two cooling towers of different companies, the waste water treatment plants (WWTP) of the city and one company as well as water samples of the river Wester and its branches.

Epidemiological investigation and case-control study: a Legionnaires' disease outbreak associated with cooling towers in Warstein, Germany, August-September 2013.

Between 1 August and 6 September 2013, an outbreak of Legionnaires' disease (LD) with 159 suspected cases occurred in Warstein, North Rhine-Westphalia, Germany. The outbreak consisted of 78 laboratory-confirmed cases of LD, including one fatality, with a case fatality rate of 1%. Legionella pneumophila, serogroup 1, subtype Knoxville, sequence type 345, was identified as the epidemic strain. A case-control study was conducted to identify possible sources of infection. In univariable analysis, cases were almost five times more likely to smoke than controls (odds ratio (OR): 4.81; 95% confidence interval (CI): 2.33-9.93; p < 0.0001). Furthermore, cases were twice as likely to live within a 3 km distance from one identified infection source as controls (OR: 2.14; 95% CI: 1.09-4.20; p < 0.027). This is the largest outbreak of LD in Germany to date. Due to a series of uncommon events, this outbreak was most likely caused by multiple sources involving industrial cooling towers. Quick epidemiological assessment, source tracing and shutting down of potential sources as well as rapid laboratory testing and early treatment are necessary to reduce morbidity and mortality. Maintenance of cooling towers must be carried out according to specification to prevent similar LD outbreaks in the future.

Hospital-acquired legionellosis originating from a cooling tower during a period of thermal inversion.

A case of hospital-acquired legionellosis occurred in a 75-year-old male patient who underwent surgery due to malignant melanoma. Legionellosis was proven by culture of Legionella pneumophila serogroup 1 from bronchoalveolar lavage (BAL) fluid. Being a chronic smoker the patient used to visit the sickroom balcony that was located about 90 m to the west of a hospital cooling tower. Routine cooling tower water samples drawn during the presumed incubation period revealed 1.0x10(4) CFU/100 ml (L. pneumophila serogroup 1). One of three isolates from the cooling tower water matched the patient's isolate by monoclonal antibody (mab)- and genotyping (sequence-based typing). Horizontal transport of cooling tower aerosols probably was favoured by meteorological conditions with thermal inversion. The case report stresses the importance of routine maintenance and microbiological control of hospital cooling towers.