Outbreaks of Legionnaires' Disease and Pontiac Fever 2006-2017.

PURPOSE OF REVIEW: The global importance of Legionnaires' disease (LD) and Pontiac fever (PF) has grown in recent years. While sporadic cases of LD and PF do not always provide contextual information for evaluating causes and drivers of Legionella risks, analysis of outbreaks provides an opportunity to assess these factors. RECENT FINDINGS: A review was performed and provides a summary of LD and PF outbreaks between 2006 and 2017. Of the 136 outbreaks, 115 were LD outbreaks, 4 were PF outbreaks, and 17 were mixed outbreaks of LD and PF. Cooling towers were implicated or suspected in the a large portion of LD or PF outbreaks (30% total outbreaks, 50% confirmed outbreak-associated cases, and 60% outbreak-associated deaths) over this period of time, while building water systems and pools/spas were also important contributors. Potable water/building water system outbreaks seldom identify specific building water system or fixture deficiencies. The outbreak data summarized here provides information for prioritizing and targeting risk analysis and mitigation strategies.

Amplicon-based taxonomic characterization of bacteria in urban and peri-urban roof-harvested rainwater stored in tanks.

Overall, 26% of Australian households use rainwater tanks as a source of potable and nonpotable water. Limited information is available on the total bacterial communities in tank water. Therefore, identification of dominant bacterial communities, diversity, and their distribution is important in understanding the microbial quality of tank water. In this study, the abundance and diversity of bacterial communities in 88 tank water samples collected from the urban areas of Brisbane (n=44) and the peri-urban center of Currumbin (n=44) in Southeast Queensland, Australia were determined using amplicon-based Illumina next-generation sequencing. In addition, the SourceTracker program was used to identify the sources of fecal contamination in tank water samples. Sequence reads were also analyzed to detect potential bacterial pathogenic genera in the tank water samples collected. Differences in sample coverage, alpha diversity, and richness did not differ significantly between the Brisbane and Currumbin tank water samples. Comamonadaceae and Planctomycetaceae were the most abundant families in all tank water samples. Curvibacter was the most abundant genus in all tank water samples. SourceTracker revealed that around 34% (Brisbane) and 43% (Currumbin) of tank water samples had a signature for bird fecal contamination. The potential opportunistic pathogenic genera including Burkholderia, Chromobacterium, Clostridium, Legionella, Mycobacterium, Nocardia, and Pseudomonas were most prevalent in tank water samples. Next-generation sequencing can be used as an initial screening tool to identify a wide array of potential pathogenic genera in tank water samples followed by quantifying specific pathogen(s) of interest using more sensitive molecular assays such as quantitative PCR (qPCR).

Public health implications of Acanthamoeba and multiple potential opportunistic pathogens in roof-harvested rainwater tanks.

A study of six potential opportunistic pathogens (Acanthamoeba spp., Legionella spp., Legionella longbeachae, Pseudomonas aeruginosa, Mycobacterium avium and Mycobacterium intracellulare) and an accidental human pathogen (Legionella pneumophila) in 134 roof-harvested rainwater (RHRW) tank samples was conducted using quantitative PCR (qPCR). All five opportunistic pathogens and accidental pathogen L. pneumophila were detected in rainwater tanks except Legionella longbeachae. Concentrations ranged up to 3.1×10(6) gene copies per L rainwater for Legionella spp., 9.6×10(5) gene copies per L for P. aeruginosa, 6.8×10(5) gene copies per L for M. intracellulare, 6.6×10(5) gene copies per L for Acanthamoeba spp., 1.1×10(5) gene copies per L for M. avium, and 9.8×10(3) gene copies per L for L. pneumophila. Among the organisms tested, Legionella spp. (99% tanks) were the most prevalent followed by M. intracellulare (78%). A survey of tank-owners provided data on rainwater end-uses. Fecal indicator bacteria (FIB) Escherichia coli and Enterococcus spp. were enumerated using culture-based methods, and assessed for correlations with opportunistic pathogens and L. pneumophila tested in this study. Opportunistic pathogens did not correlate well with FIB except E. coli vs. Legionella spp. (tau=0.151, P=0.009) and E. coli vs. M. intracellulare (tau=0.14, P=0.015). However, M. avium weakly correlated with both L. pneumophila (Kendall's tau=0.017, P=0.006) and M. intracellulare (tau=0.088, P=0.027), and Legionella spp. also weakly correlated with M. intracellulare (tau=0.128, P=0.028). The presence of these potential opportunistic pathogens in tank water may present health risks from both the potable and non-potable uses documented from the current survey data.

Evidence of Avian and Possum Fecal Contamination in Rainwater Tanks as Determined by Microbial Source Tracking Approaches.

UNLABELLED: Avian and possum fecal droppings may negatively impact roof-harvested rainwater (RHRW) water quality due to the presence of zoonotic pathogens. This study was aimed at evaluating the performance characteristics of a possum feces-associated (PSM) marker by screening 210 fecal and wastewater samples from possums (n = 20) and a range of nonpossum hosts (n = 190) in Southeast Queensland, Australia. The host sensitivity and specificity of the PSM marker were 0.90 and 0.95 (maximum value, 1.00), respectively. The mean concentrations of the GFD marker in possum fecal DNA samples (8.8 × 10(7) gene copies per g of feces) were two orders of magnitude higher than those in the nonpossum fecal DNA samples (5.0 × 10(5) gene copies per g of feces). The host sensitivity, specificity, and concentrations of the avian feces-associated GFD marker were reported in our recent study (W. Ahmed, V. J. Harwood, K. Nguyen, S. Young, K. Hamilton, and S. Toze, Water Res 88:613-622, 2016, http://dx.doi.org/10.1016/j.watres.2015.10.050). The utility of the GFD and PSM markers was evaluated by testing a large number of tank water samples (n = 134) from the Brisbane and Currumbin areas. GFD and PSM markers were detected in 39 of 134 (29%) and 11 of 134 (8%) tank water samples, respectively. The GFD marker concentrations in PCR-positive samples ranged from 3.7 × 10(2) to 8.5 × 10(5) gene copies per liter, whereas the concentrations of the PSM marker ranged from 2.0 × 10(3) to 6.8 × 10(3) gene copies per liter of water. The results of this study suggest the presence of fecal contamination in tank water samples from avian and possum hosts. This study has established an association between the degradation of microbial tank water quality and avian and possum feces. Based on the results, we recommend disinfection of tank water, especially for tanks designated for potable use. IMPORTANCE: The use of roof-harvested rainwater (RHRW) for domestic purposes is a globally accepted practice. The presence of pathogens in rainwater tanks has been reported by several studies, supporting the necessity for the management of potential health risks. The sources of fecal pollution in rainwater tanks are unknown. However, the application of microbial source tracking (MST) markers has the potential to identify the sources of fecal contamination in a rainwater tank. In this study, we provide evidence of avian and possum fecal contamination in tank water samples using molecular markers. This study established a potential link between the degradation of the microbial quality of tank water and avian and possum feces.

Dose-response algorithms for water-borne Pseudomonas aeruginosa folliculitis.

We developed two dose-response algorithms for P. aeruginosa pool folliculitis using bacterial and lesion density estimates, associated with undetectable, significant, and almost certain folliculitis. Literature data were fitted to Furumoto & Mickey's equations, developed for plant epidermis-invading pathogens: N l = A ln(1 + BC) (log-linear model); P inf = 1-e(-r c C) (exponential model), where A and B are 2.51644 × 107 lesions/m2 and 2.28011 × 10-11 c.f.u./ml P. aeruginosa, respectively; C = pathogen density (c.f.u./ml), N l = folliculitis lesions/m2, P inf = probability of infection, and r C = 4·3 × 10-7 c.f.u./ml P. aeruginosa. Outbreak data indicates these algorithms apply to exposure durations of 41 ± 25 min. Typical water quality benchmarks (≈10-2 c.f.u./ml) appear conservative but still useful as the literature indicated repeated detection likely implies unstable control barriers and bacterial bloom potential. In future, culture-based outbreak testing should be supplemented with quantitative polymerase chain reaction and organic carbon assays, and quantification of folliculitis aetiology to better understand P. aeruginosa risks.

Pseudomonas aeruginosa dose response and bathing water infection.

Pseudomonas aeruginosa is the opportunistic pathogen mostly implicated in folliculitis and acute otitis externa in pools and hot tubs. Nevertheless, infection risks remain poorly quantified. This paper reviews disease aetiologies and bacterial skin colonization science to advance dose-response theory development. Three model forms are identified for predicting disease likelihood from pathogen density. Two are based on Furumoto & Mickey's exponential 'single-hit' model and predict infection likelihood and severity (lesions/m2), respectively. 'Third-generation', mechanistic, dose-response algorithm development is additionally scoped. The proposed formulation integrates dispersion, epidermal interaction, and follicle invasion. The review also details uncertainties needing consideration which pertain to water quality, outbreaks, exposure time, infection sites, biofilms, cerumen, environmental factors (e.g. skin saturation, hydrodynamics), and whether P. aeruginosa is endogenous or exogenous. The review's findings are used to propose a conceptual infection model and identify research priorities including pool dose-response modelling, epidermis ecology and infection likelihood-based hygiene management.

Dose-response time modelling for highly pathogenic avian influenza A (H5N1) virus infection.

AIMS: To develop time-dependent dose-response models for highly pathogenic avian influenza A (HPAI) of the H5N1 subtype virus. METHODS AND RESULTS: A total of four candidate time-dependent dose-response models were fitted to four survival data sets for animals (mice or ferrets) exposed to graded doses of HPAI H5N1 virus using the maximum-likelihood estimation. A beta-Poisson dose-response model with the N(50) parameter modified by an exponential-inverse-power time dependency or an exponential dose-response model with the k parameter modified by an exponential-inverse time dependency provided a statistically adequate fit to the observed survival data. CONCLUSIONS: We have successfully developed the time-dependent dose-response models to describe the mortality of animals exposed to an HPAI H5N1 virus. The developed model describes the mortality over time and represents observed experimental responses accurately. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study describing time-dependent dose-response models for HPAI H5N1 virus. The developed models will be a useful tool for estimating the mortality of HPAI H5N1 virus, which may depend on time postexposure, for the preparation of a future influenza pandemic caused by this lethal virus.

Incorporating time postinoculation into a dose-response model of Yersinia pestis in mice.

AIMS: To develop a time-dependent dose-response model for describing the survival of animals exposed to Yersinia pestis. METHODS AND RESULTS: Candidate time-dependent dose-response models were fitted to a survival data set for mice intraperitoneally exposed to graded doses of Y. pestis using the maximum likelihood estimation method. An exponential dose-response model with the model parameter modified by an inverse-power dependency of time postinoculation provided a statistically adequate fit to the experimental survival data. This modified model was verified by comparison with prior studies. CONCLUSIONS: The incorporated time dependency quantifies the expected temporal effect of in vivo bacteria growth in the dose-response relationship. The modified model describes the development of animal infectious response over time and represents observed responses accurately. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study to incorporate time in a dose-response model for Y. pestis infection. The outcome may be used for the improved understanding of in vivo bacterial dynamics, improved postexposure decision making or as a component to better assist epidemiological investigations.

Dose-response model for Burkholderia pseudomallei (melioidosis).

AIMS: The objective of this study was development of a dose-response model for exposure to Burkholderia pseudomallei in different animal hosts and analysis of the results. The data sets with which the model was developed were taken from the open literature. METHODS AND RESULTS: All data sets were initially tested for a trend between dose and outcome using the Cochran-Armitage test. Only data showing a statistically significant trend were subjected to further analysis (fitting with parametric dose-response relationships). Dose-response relationships (exponential, beta-Poisson and log-probit) were fit to data using the method of maximum likelihood estimation. CONCLUSIONS: Dose-response analysis of BALB/c mice, C57BL/6 mice, guinea pigs and diabetic rats showed that BALB/c mice exposed intranasally (i.n.) and guinea pigs exposed intraperitoneally (i.p.) are significantly more sensitive to B. pseudomallei than C57BL/6 mice exposed i.n. and diabetic rats exposed i.p. SIGNIFICANCE AND IMPACT OF THE STUDY: The results confirmed the findings of a study of outbreak data that the diabetic population is more susceptible to infection with B. pseudomallei than the general population. The low dose prediction from best fit dose-response models can be used to draw guidelines for public health decision making processes, including consideration of sensitive subpopulations.

A quantitative microbial risk assessment model for Legionnaires' disease: animal model selection and dose-response modeling.

Legionnaires' disease (LD), first reported in 1976, is an atypical pneumonia caused by bacteria of the genus Legionella, and most frequently by L. pneumophila (Lp). Subsequent research on exposure to the organism employed various animal models, and with quantitative microbial risk assessment (QMRA) techniques, the animal model data may provide insights on human dose-response for LD. This article focuses on the rationale for selection of the guinea pig model, comparison of the dose-response model results, comparison of projected low-dose responses for guinea pigs, and risk estimates for humans. Based on both in vivo and in vitro comparisons, the guinea pig (Cavia porcellus) dose-response data were selected for modeling human risk. We completed dose-response modeling for the beta-Poisson (approximate and exact), exponential, probit, logistic, and Weibull models for Lp inhalation, mortality, and infection (end point elevated body temperature) in guinea pigs. For mechanistic reasons, including low-dose exposure probability, further work on human risk estimates for LD employed the exponential and beta-Poisson models. With an exposure of 10 colony-forming units (CFU) (retained dose), the QMRA model predicted a mild infection risk of 0.4 (as evaluated by seroprevalence) and a clinical severity LD case (e.g., hospitalization and supportive care) risk of 0.0009. The calculated rates based on estimated human exposures for outbreaks used for the QMRA model validation are within an order of magnitude of the reported LD rates. These validation results suggest the LD QMRA animal model selection, dose-response modeling, and extension to human risk projections were appropriate.

A national study on the residential impact of biological aerosols from the land application of biosolids.

AIMS: The purpose of this study was to evaluate the community risk of infection from bioaerosols to residents living near biosolids land application sites. METHODS AND RESULTS: Approximately 350 aerosol samples from 10 sites located throughout the USA were collected via the use of six SKC Biosamplers. Downwind aerosol samples from biosolids loading, unloading, land application and background operations were collected from all sites. All samples were analysed for the presence of HPC bacteria, total coliform bacteria, Escherichia coli, Clostridium perfringens, coliphage, enteroviruses, hepatitis A virus and norovirus. Total coliforms, E. coli, C. perfringens and coliphage were not detected with great frequency from any sites, however, biosolids loading operations resulted in the largest concentrations of these aerosolized microbial indicators. Microbial risk analyses were conducted on loading and land application operations and their subsequent residential exposures determined. CONCLUSIONS: The greatest annual risks of infection occurred during loading operations, and resulted in a 4 x 10(-4) chance of infection from inhalation of coxsackievirus A21. Land application of biosolids resulted in risks that were <2 x 10(-4) from inhalation of coxsackievirus A21. Overall bioaerosol exposure from biosolids operations poses little community risk based on this study. SIGNIFICANCE AND IMPACT OF THE STUDY: This study evaluated the overall incidence of aerosolized micro-organisms from the land application of biosolids and subsequently determined that microbial risks of infection were low for residents close to biosolids application sites.

Estimation of bioaerosol risk of infection to residents adjacent to a land applied biosolids site using an empirically derived transport model.

AIM: The purpose of this study was to develop an empirically derived transport model, which could be used to predict downwind concentrations of viruses and bacteria during land application of liquid biosolids and subsequently assess microbial risk associated with this practice. METHODS AND RESULTS: To develop the model, coliphage MS-2 and Escherichia coli were aerosolized after addition to water within a biosolids spray application truck, and bioaerosols were collected at discrete downwind distances ranging from 2 to 70 m. Although coliphage were routinely detected, E. coli did not frequently survive aerosolization. Data on aerosolized coliphage was then used to generate a virus transport model. Risks of infection were calculated for various ranges of human virus concentrations that could be found in biosolids. CONCLUSIONS: A conservative estimate at 30.5 m (assumed to be nearest adjacent residences) downwind, resulted in risks of infection of 1 : 100,000, to the more realistic 1 : 10,000,000 per exposure. Conservative annual risks were calculated to be no more than 7 : 100,000 where as a more realistic risk was no greater than 7 : 10,000,000. Overall, the viral risk to residences adjacent to land application sites appears to be low, both for one time and annual probabilities of infection. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrated a simple approach towards modelling viral pathogens aerosolized from land applied liquid biosolids, and offers insight into the associated viral risk.

Quantitative assessment of risk reduction from hand washing with antibacterial soaps.

The Centers for Disease Control and Prevention have estimated that there are 3,713,000 cases of infectious disease associated with day care facilities each year. The objective of this study was to examine the risk reduction achieved from using different soap formulations after diaper changing using a microbial quantitative risk assessment approach. To achieve this, a probability of infection model and an exposure assessment based on micro-organism transfer were used to evaluate the efficacy of different soap formulations in reducing the probability of disease following hand contact with an enteric pathogen. Based on this model, it was determined that the probability of infection ranged from 24/100 to 91/100 for those changing diapers of babies with symptomatic shigellosis who used a control product (soap without an antibacterial ingredient), 22/100 to 91/100 for those who used an antibacterial soap (chlorohexadine 4%), and 15/100 to 90/100 for those who used a triclosan (1.5%) antibacterial soap. Those with asymptomatic shigellosis who used a non-antibacterial control soap had a risk between 49/100,000 and 53/100, those who used the 4% chlorohexadine-containing soap had a risk between 43/100,000 and 51/100, and for those who used a 1.5% triclosan soap had a risk between 21/100,000 and 43/100. The adequate washing of hands after diapering reduces risk and can be further reduced by a factor of 20% by the use of an antibacterial soap. Quantitative risk assessment is a valuable tool in the evaluation of household sanitizing agents and low risk outcomes.

Quantitative assessment of risk reduction from hand washing with antibacterial soaps.

The Centers for Disease Control and Prevention have estimated that there are 3,713,000 cases of infectious disease associated with day care facilities each year. The objective of this study was to examine the risk reduction achieved from using different soap formulations after diaper changing using a microbial quantitative risk assessment approach. To achieve this, a probability of infection model and an exposure assessment based on micro-organism transfer were used to evaluate the efficacy of different soap formulations in reducing the probability of disease following hand contact with an enteric pathogen. Based on this model, it was determined that the probability of infection ranged from 24/100 to 91/100 for those changing diapers of babies with symptomatic shigellosis who used a control product (soap without an antibacterial ingredient), 22/100 to 91/100 for those who used an antibacterial soap (chlorohexadine 4%), and 15/100 to 90/100 for those who used a triclosan (1.5%) antibacterial soap. Those with asymptomatic shigellosis who used a non-antibacterial control soap had a risk between 49/100,000 and 53/100, those who used the 4% chlorohexadine-containing soap had a risk between 43/100,000 and 51/100, and for those who used a 1.5% triclosan soap had a risk between 21/100,000 and 43/100. The adequate washing of hands after diapering reduces risk and can be further reduced by a factor of 20% by the use of an antibacterial soap. Quantitative risk assessment is a valuable tool in the evaluation of household sanitizing agents and low risk outcomes.

Progress and data gaps in quantitative microbial risk assessment.

Quantitative microbial risk assessment (QMRA) has emerged as a useful tool to develop criteria for human exposures to pathogens. There is opportunity to extend the usefulness of this tool in water and other applications if new fundamental information can be obtained to complement existing data. Such information includes effects of strain and host differences, population level disease dynamics, and ability of animal data to serve as a predictor of human potency. This paper reviews the development of QMRA and outlines the nature of additional data that would be useful for its development.

Development of a dose-response relationship for Escherichia coli O157:H7.

E. coli O157:H7 is an emerging food and waterborne pathogen. The development of acceptable guidelines for exposure to this organism based on quantitative microbial risk assessment requires a dose response curve. In this study, a prior animal study was used to develop a dose response relationship. The data was adequately fit by the beta-Poisson dose response relationship. This relationship was validated with reference to two outbreaks of this organism. It was found that the low dose extrapolation of the animal data using the beta-Poisson relationship provided estimates of risk concordant with those noted in the outbreaks. The fitted dose response relationship in conjunction with population estimates of the prevalence of E. coli O157:H7 illness indicates that the overall exposure is quite low in the US.

Epidemiology, microbiology, and risk assessment of waterborne pathogens including Cryptosporidium.

Cryptosporidium is one of a suite of relatively recently emerging pathogens of concern in drinking water. Based on human dose-response tests, guidelines for exposure yielding defined levels of endemic risk have been developed. This risk assessment procedure is grounded in the process used for chemical risk assessment. From outbreak data, critical concentrations in water that may lead to epidemic levels have been postulated. Development of these levels will be discussed. Validation of the information using outbreak reports from the 1993 Milwaukee incident can be made. Use of this approach must be tempered by the existence of substantial waterborne cases in the absence of detectable oocyst levels as in the Las Vegas outbreak, and (apparent) high levels of oocysts without (apparent) significant health effects as in the case of the (at the time of this writing) ongoing incident in Sydney, Australia.

A risk assessment framework for the evaluation of skin infections and the potential impact of antibacterial soap washing.

Antibacterial soaps may have an important role in the control of skin infection. However, quantitative estimation of their benefit is difficult because of the problems associated with conducting epidemiologic studies. An alternative benefit estimation approach, quantitative microbial risk assessment, has application to this problem. This article sets forth the quantitative microbial risk assessment method and applies it specifically to the estimation of the reduction in risk of dermal infection from Staphylococcus aureus resulting from use of antibacterial soaps. A dose-response model was formulated by using available information on growth kinetics of the organism on the skin and dose data based on the inoculation of the forearm skin in volunteers. A predictive relationship for microbial growth on the skin was developed. These data were limited, and clearly more studies are needed on inoculation at more than one site and growth leading to infection on the skin with and without the use of germicidal soaps.However, by using relationships based on extant data sets, it was estimated that the use of germicidal soap could result in a substantial reduction in the risk of infection by S aureus. The estimated risk reduction was in general concordance with published results from epidemiologic studies conducted on military cadets. The methodology of quantitative microbial risk assessment has thus been shown to be applicable to this problem and may have broader applicability in other personal hygiene contexts.

Use of quantitative microbial risk assessment for evaluation of the benefits of laundry sanitation.

The goal of this study was to evaluate the risk assessment process for quantifying the contribution of contamination in the home to microbial infections. Whereas risks of enteric pathogens spread through food has been assessed, the spread of fecal-oral pathogens through surfaces likely at low rates would be difficult to address through epidemiologic studies. An alternative is quantitative risk assessment. The 4-step process of hazard identification, dose-response, exposure assessment, and risk characterization can be used; however, exposure assessment may follow a complicated pathway consisting of survival and transference. Microbial hazards in the home have focused primarily on enteric bacteria. Dose-response data are available; however, the transfer from the hands to the dose is uncertain. Through day care studies, Shigella has been shown to be transferred in this manner, and a dose-response model is available. By using these data and information on the transference of bacteria between clothing and hands, risk estimates were made for contaminated laundry. Risks were calculated as high as 10 per million population to much lower levels associated with lower excretion rates of the bacteria in the feces. Approximately a 90% and 99% reduction in the probability of disease through laundering and use of a sanitizing detergent, respectively, were suggested by the models. Better data are needed on incidence of disease in the population, excretion rates over the course of an infection, amount of feces spread in the home, distribution of bacteria, survival, and the transfer of the bacteria from surfaces to the hands and to the mouth.