Editorial commentary: risk assessment and prediction for health care-associated Legionnaires' disease: percent distal site positivity as a cut-point

Understanding the distribution of positiveLegionellasamples in healthcare-premise water systems: Using statistical analysis to determine a distribution forLegionellaand to support sample size recommendations

Objective:

To significantly fit a statistical distribution to the proportion of positiveLegionellasamples in a series of water samples from multiple facility-premise water systems.

Design:

Statistical fit test.

Setting:

A hospital and associated long-term care facility (LTCF) in New York State, as well as temporal and culture data from a deidentified hospital site supplied by one of the vendor laboratories.

Methods:

Culture samples (n = 1,393) were segmented into 139 test cycles with roughly 10 samples in each. The proportion of positive samples was standardized to 25 total samples per test to give a distribution of discrete values. These values were analyzed for fit with the following discrete distributions: Poisson, negative binomial, geometric, and zero-inflated Poisson.

Results:

The zero-inflated Poisson distribution fitted to the copper–silver ionization (CSI)-treated and untreated test cycles indicates that 88% of the expected positive proportions should occur by the 30% cutoff (rounded up to 8 positive samples among 25 total samples), similar to the 93% expectation for just CSI-treated test cycles. The other treatment in these data (chlorine dioxide) was not effective in treatingLegionellain the sampled buildings, and if there is an underlying distribution to these specific test cycles, it is not the zero-inflated Poisson distribution.

Conclusions:

In a well-maintained or well-treated premise water distribution system, ~30% or lower proportion of positiveLegionellasamples should occur. Anything above that cutoff is either very unlikely or not expected at all and indicates a problem in the water system.

Modelling characteristics to predict Legionella contamination risk - Surveillance of drinking water plumbing systems and identification of risk areas

For the surveillance of drinking water plumbing systems (DWPS) and the identification of risk factors, there is a need for an early estimation of the risk of Legionella contamination within a building, using efficient and assessable parameters to estimate hazards and to prioritize risks. The precision, accuracy and effectiveness of ways of estimating the risk of higher Legionella numbers (temperature, stagnation, pipe materials, etc.) have only rarely been empirically assessed in practice, although there is a broad consensus about the impact of these risk factors. We collected n = 807 drinking water samples from 9 buildings which had had Legionella spp. occurrences of >100 CFU/100mL within the last 12 months, and tested for Legionella spp., L. pneumophila, HPC 20°C and 36°C (culture-based). Each building was sampled for 6 months under standard operating conditions in the DWPS. We discovered high variability (up to 4 log(10) steps) in the presence of Legionella spp. (CFU/100 mL) within all buildings over a half year period as well as over the course of a day. Occurrences were significantly correlated with temperature, pipe length measures, and stagnation. Logistic regression modelling revealed three parameters (temperature after flushing until no significant changes in temperatures can be obtained, stagnation (low withdrawal, qualitatively assessed), pipe length proportion) to be the best predictors of Legionella contamination (>100 CFU/100 mL) at single outlets (precision = 66.7%; accuracy = 72.1%; F(0.5) score = 0.59).

Use of copper-silver ionization for the control of legionellae in alkaline environments at health care facilities

BACKGROUND

There are multiple treatment options for the control of legionellae in premise hot water systems. Water chemistry plays a role in the efficacy of these treatments and should be considered when selecting a treatment. This study demonstrated the efficacy of copper-silver ionization (CSI) under alkaline water conditions in 2 health care facilities.

METHODS

Monitoring for copper (Cu) and silver (Ag) ions was performed, and the corresponding percentage of positive Legionella cultures was monitored. Low Legionella colony forming units (CFU), with a mean <10 CFU/100 mL, and ≤30% positive culture for each sampling period, along with no recurrent disease, were considered indicative of control.

RESULTS

CSI treatment was shown to reduce both the number of CFU found and the percentage of samples found to be culture positive. After treatment was established, culture positivity was, for example, reduced from 70% (>10(3) CFU/100 mL) to consistently <30% (38 CFU/100 mL).

CONCLUSION

Control of legionellae in premise water systems may be a complex process requiring long-term assessments for adequate control. This work found that CSI could be successful in controlling Legionella under alkaline water conditions, and the evidence suggests that Ag ions are responsible for the control of Legionella pneumophila 1, L pneumophila 6, and L anisa.

Temperature diagnostic to identify high risk areas and optimize Legionella pneumophila surveillance in hot water distribution systems

Legionella pneumophila is frequently detected in hot water distribution systems and thermal control is a common measure implemented by health care facilities. A risk assessment based on water temperature profiling and temperature distribution within the network is proposed, to guide effective monitoring strategies and allow the identification of high risk areas. Temperature and heat loss at control points (water heater, recirculation, representative points-of-use) were monitored in various sections of five health care facilities hot water distribution systems and results used to develop a temperature-based risk assessment tool. Detailed investigations show that defective return valves in faucets can cause widespread temperature losses because of hot and cold water mixing. Systems in which water temperature coming out of the water heaters was kept consistently above 60 °C and maintained above 55 °C across the network were negative for Legionella by culture or qPCR. For systems not meeting these temperature criteria, risk areas for L. pneumophila were identified using temperature profiling and system's characterization; higher risk was confirmed by more frequent microbiological detection by culture and qPCR. Results confirmed that maintaining sufficiently high temperatures within hot water distribution systems suppressed L. pneumophila culturability. However, the risk remains as shown by the persistence of L. pneumophila by qPCR.