Universal decontamination of hospital surfaces in an occupied inpatient room with a continuous 405 nm light source.

BACKGROUND: Previous work has shown that a ceiling-mounted, 405 nm high-intensity narrow-spectrum light environmental decontamination system (HINS-light EDS) reduces bacterial contamination of environmental surfaces in a burns unit by between 27% and 75%. Examination of the efficacy of the light over extended exposure times and its probable mode of action was performed. AIM: To ascertain the correlation between bacterial kill achieved on sampled surface sites around the burns unit and both irradiance levels of the 405 nm light, and exposure time. METHODS: Seventy samples were taken using contact agar plates from surfaces within an occupied side-room in the burns unit before, during, and after a seven-day use of the HINS-light EDS. This was repeated in three separate studies. Statistical analysis determined whether there was significant decrease in environmental contamination during prolonged periods of HINS-light treatment, and whether there was an association between irradiance and bacterial kill. FINDINGS: A decrease of between 22% and 86% in the mean number of surface bacteria was shown during the use of the HINS-light EDS. When the light ceased to be used, increases of between 78% and 309% occurred. There was no correlation between bacterial kill and irradiance levels at each sampling site but strong correlation between bacterial kill and exposure time. CONCLUSION: Prolonged exposure to the HINS-light EDS causes a cumulative decontamination of the surfaces within a burns unit. The importance of exposure time and possible airborne effect over irradiance levels is emphasized.

405 nm light technology for the inactivation of pathogens and its potential role for environmental disinfection and infection control.

BACKGROUND: Although the germicidal properties of ultraviolet (UV) light have long been known, it is only comparatively recently that the antimicrobial properties of visible violet-blue 405 nm light have been discovered and used for environmental disinfection and infection control applications. AIM: To review the antimicrobial properties of 405 nm light and to describe its application as an environmental decontamination technology with particular reference to disinfection of the hospital environment. METHODS: Extensive literature searches for relevant scientific papers and reports. FINDINGS: A large body of scientific evidence is now available that provides underpinning knowledge of the 405 nm light-induced photodynamic inactivation process involved in the destruction of a wide range of prokaryotic and eukaryotic microbial species, including resistant forms such as bacterial and fungal spores. For practical application, a high-intensity narrow-spectrum light environmental disinfection system (HINS-light EDS) has been developed and tested in hospital isolation rooms. The trial results have demonstrated that this 405 nm light system can provide continuous disinfection of air and exposed surfaces in occupied areas of the hospital, thereby substantially enhancing standard cleaning and infection control procedures. CONCLUSION: Violet-blue light, particularly 405 nm light, has significant antimicrobial properties against a wide range of bacterial and fungal pathogens and, although germicidal efficacy is lower than UV light, this limitation is offset by its facility for safe, continuous use in occupied environments. Promising results on disinfection efficacy have been obtained in hospital trials but the full impact of this technology on reduction of healthcare-associated infection has yet to be determined.

Detection of emamectin benzoate tolerance emergence in different life stages of sea lice, Lepeophtheirus salmonis, on farmed Atlantic salmon, Salmo salar L.

Emamectin benzoate has been used to treat sea lice, Lepeophtheirus salmonis, infestations on farmed Atlantic salmon, Salmo salar. Recent evidence suggests a reduction in effectiveness in some locations. A major challenge in the detection of tolerance emergence can be the typically low proportion of resistant individuals in a population during the early phases. The objectives of this study were to develop a method for determining differences in temporal development of tolerance between sea lice life stages and to explore how these differences might be used to improve the monitoring of treatment effectiveness in a clinical setting. This study examined two data sets based on records of sea lice abundance following emamectin benzoate treatments from the west coast of Scotland (2002-2006) and from New Brunswick, Canada (2004-2008). Life stages were categorized into two groups (adult females and the remaining mobile stages) to examine the trends in mean abundance and treatment effectiveness. Differences in emamectin benzoate effectiveness were found between the two groups by year and location, suggesting that an important part of monitoring drug resistance development in aquatic ectoparasites may be the need to focus on key life stages.

Use of agent-based modelling to predict benefits of cleaner fish in controlling sea lice, Lepeophtheirus salmonis, infestations on farmed Atlantic salmon, Salmo salar L.

Sea lice, Lepeophtheirus salmonis, are ectoparasites of farmed and wild salmonids. Infestations can result in significant morbidity and mortality of hosts in addition to being costly to control. Integrated pest management programmes have been developed to manage infestations, and in some salmon farming areas, these programmes include the use of wrasse. Wrasse prey upon the parasitic life stages of L. salmonis and can be stocked on farms at varying densities. Despite considerable variation in the usage of wrasse, there are few quantitative estimates of how well they can control sea lice and how best to optimize their use. To explore at what densities wrasse should be stocked in order to meet specific control targets, we built an individual-based model that simulates sea lice infestation patterns on a representative salmonid host. Sea lice can be controlled through the use of chemical treatments as well as by wrasse predators. We found that the wrasse can effectively control sea lice, and the densities of wrasse needed for effective control depend upon the source of the infestation and the targeted level of control. Effective usage of wrasse can result in decreased use of chemical treatments and improved control of sea lice.

EU sampling strategies for the detection of veterinary drug residues in aquaculture species: are they working?

Over the past 50 years, the culture of aquatic species in controlled conditions to enhance production has grown in importance and now provides nearly 50% of the world's seafood supply. In part, this expansion has been made possible by the use of antibiotics, antifungals, and other veterinary medicines to control disease and improve welfare. Despite guidelines being available, the sampling programmes for drug residue surveillance of aquaculture products recommended by the CODEX Alimentarius Commission were withdrawn in 2008 and put under review. Directive 96/23/EC sets out legislation to govern how sampling programmes for drug residue surveillance should be conducted within the EU. This directive applies both to produce raised within the EU and also imported products from third countries. This communication examines the existing EU sampling regimen for aquaculture products and comments on its possible application in a global context. We examine UK statutory sampling data that, while indicating the effectiveness of the directive, also suggests that the directive may lead to unnecessary sampling. Regarding imports, examination of the Rapid Alert System for Food and Feed (RASFF) database using process control charts and statistical modelling suggests that the sampling regimen described in the directive is effective but not sufficiently flexible for the range of aquaculture practices that exist. Limitations of the directive, datasets, and practices are further discussed.

Herd-level risk factors of bovine tuberculosis in England and Wales after the 2001 foot-and-mouth disease epidemic.

OBJECTIVES: We present the results of a 2005 case-control study of bovine tuberculosis (bTB) breakdowns in English and Welsh herds. The herd management, farming practices, and environmental factors of 401 matched pairs of case and control herds were investigated to provide a picture of herd-level risk factors in areas of varying bTB incidence. METHODS: A global conditional logistic regression model, with region-specific variants, was used to compare case herds that had experienced a confirmed bTB breakdown to contemporaneous control herds matched on region, herd type, herd size, and parish testing interval. RESULTS: Contacts with cattle from contiguous herds and sourcing cattle from herds with a recent history of bTB were associated with an increased risk in both the global and regional analyses. Operating a farm over several premises, providing cattle feed inside the housing, and the presence of badgers were also identified as significantly associated with an increased bTB risk. CONCLUSIONS: Steps taken to minimize cattle contacts with neighboring herds and altering trading practices could have the potential to reduce the size of the bTB epidemic. In principle, limiting the interactions between cattle and wildlife may also be useful; however this study did not highlight any specific measures to implement.

Environmental decontamination of a hospital isolation room using high-intensity narrow-spectrum light.

The performance of a new decontamination technology, referred to as 'high-intensity narrow-spectrum light environmental decontamination system' (HINS-light EDS) was evaluated by a series of three studies carried out in a hospital isolation room used to treat burns patients. The ceiling-mounted HINS-light EDS emits high-intensity 405nm light which, although bactericidal, is harmless to patients and staff thereby permitting continuous environmental disinfection throughout the day. Performance efficacy was assessed by contact agar plate sampling and enumeration of staphylococcal bacteria on environmental surfaces within the room before, during and after HINS-light EDS treatment. When the room was unoccupied, use of HINS-light EDS resulted in ∼90% reduction of surface bacterial levels and when the room was occupied by an MRSA-infected burns patient, reductions between 56% and 86% were achieved, with the highest reduction (86%) measured following an extended period of HINS-light EDS operation. In an on/off intervention study, surface bacterial levels were reduced by 62% by HINS-light EDS treatment and returned to normal contamination levels two days after the system was switched off. These reductions of staphylococci, including Staphylococcus aureus and meticillin-resistant S. aureus, by HINS-light EDS treatment were greater than the reductions achieved by normal infection control and cleaning activities alone. The findings provide strong evidence that HINS-light EDS, used as a supplementary procedure, can make a significant contribution to bacterial decontamination in clinical environments.

The use of prevalence as a measure of lice burden: a case study of Lepeophtheirus salmonis on Scottish Atlantic salmon, Salmo salar L., farms.

This study investigates the benefits of using prevalence as a summary measure of sea lice infestation on farmed Atlantic salmon, Salmo salar L. Aspects such as sampling effort, the relationship between abundance and prevalence arising from the negative binomial distribution, and how this relationship can be used to indicate the degree of aggregation of lice on a site at a given time point are discussed. As a case study, data were drawn from over 50 commercial Atlantic salmon farms on the west coast of Scotland between 2002 and 2006. Descriptive statistics and formal analysis using a linear modelling technique identified significant variations in sea lice prevalence across year class, region and season. Supporting evidence of a functional relationship between prevalence and abundance of sea lice is provided, which is explained through the negative binomial distribution.

Temporal and spatial variations in lice numbers on salmon farms in the Hardanger fjord 2004-06.

The long and narrow Hardanger fjord in western Norway has a high density of salmon farms and has had severe salmon lice, Lepeophtheirus salmonis, problems. In the years 2004-06, salmon lice numbers were recorded in selected salmon farms in the fjord as part of a larger research project. Most farm sites participated in a strategic control programme and were deloused between November and January in each year. The aim of the programme was to achieve a mean abundance of <0.3 adult female lice at this time and to minimize the infection pressure on wild smolts in the spring. Dedicated teams carried out detailed counting of lice on farmed fish in April-September each year. Temperature conditions were fairly similar throughout the fjord and amongst years, but wide variations in salinities were observed. The two innermost zones, B and C, had the lowest lice mean abundances, whereas the outermost zones, D and E, consistently had more lice. General linear model analyses showed that differences in adult female lice abundance between the zones were associated with differing levels of salinity and emamectin benzoate treatments strategically administered. Mean fish weight was significantly positively correlated with mean abundance of adult female lice.

Changes in epidemiological patterns of sea lice infestation on farmed Atlantic salmon, Salmo salar L., in Scotland between 1996 and 2006.

Analyses of a unique database containing sea lice records over an 11 year period provide evidence of changing infestation patterns in Scotland. The data, collected from more than 50 commercial Atlantic salmon farms, indicate that both species of sea lice commonly found in Scotland, Lepeophtheirus salmonis and Caligus elongatus, have declined on farms over the past decade. Reductions for both species have been particularly marked since 2001 when more effective veterinary medicines became available. Treatment data were also available in the database and these show a growing trend towards the use of the in-feed medication emamectin benzoate (Slice), particularly in the first year of the salmon production cycle. However, this trend towards single product use has not been sustained in 2006, the latest year for which data are available. There is some evidence of region to region variation within Scotland with the Western Isles experiencing higher levels of infestation. However, compared to the levels observed between 1996 and 2000, all regions have benefited from reduced lice infestation, with the overall pattern showing a particular reduction in the second and third quarters of the second year of production.

Heart failure is common in diabetic cats: findings from a retrospective case-controlled study in first-opinion practice.

OBJECTIVES: To study the prognosis and cause of death in cats with diabetes mellitus. METHODS: Twenty consecutive cases of feline diabetes mellitus diagnosed in first-opinion practice were followed. Three control cats, without diabetes, were matched to each case of diabetes; these were also followed. RESULTS: One Somali cat with diabetes could not be matched, so complete data analysis considered only 19 diabetics and 57 matched controls. Death occurred in 14 of 20 diabetics and 23 of 57 controls although one control cat was eventually lost to follow-up. Heart disease and heart failure led to death in six diabetic cats. One of these was the non-matched Somali; nevertheless, the death rate from heart disease in the diabetics was five of 19 compared with two of 57 in controls. The relative risk of heart failure in diabetic cats was 10.4 times that of the controls; this difference in rates was statistically significant. Survival amongst diabetics was significantly worse than for controls. For the control cats median survival was 718 days after the index visit, whereas for the diabetic cases median survival was 385 days after diagnosis. CLINICAL SIGNIFICANCE: Heart disease and failure are common in diabetic cats. This observation deserves further attention.

The prevalence, distribution and severity of detectable pathological lesions in badgers naturally infected with Mycobacterium bovis.

The Randomized Badger Culling Trial (RBCT) began in 1998 to determine the impact of badger culling in controlling bovine tuberculosis in cattle. A total of 1166 badgers (14% of total) proactively culled during the RBCT were found to be tuberculous, offering a unique opportunity to study the pathology caused by Mycobacterium bovis in a large sample of badgers. Of these, 39% of adults (approximately 6% of all adults culled) had visible lesions (detectable at necropsy) of bovine tuberculosis; cubs had a lower prevalence of infection (9%) but a higher percentage of tuberculous cubs (55.5%) had visible lesions. Only approximately 1% of adult badgers had extensive, severe pathology. Tuberculous badgers with recorded bite wounds (approximately 5%) had a higher prevalence of visible lesions and a different distribution of lesions, suggesting transmission via bite wounds. However, the predominance of lesions in the respiratory tract indicates that most transmission occurs by the respiratory route.

Clustering of parasites within cages on Scottish and Norwegian salmon farms: alternative sampling strategies illustrated using simulation.

Within the literature, most discussion of sampling protocols for monitoring aquatic parasites is based on the assumptions of simple random sampling. Recent research has shown that in monitoring parasite abundance on fish farms composed of discrete cages, care must be taken to properly account for the clustering which naturally occurs. This paper illustrates the effect of clustering in the context of monitoring ectoparasitic sea lice Lepeophtheirus salmonis and Caligus elongatus in salmon farms. The degree of clustering of sea lice infections in fish within cages is measured using the intraclass correlation coefficient (ICC). A wide range of ICC values from sites in Scotland and Norway were estimated for the chalimus and mobile stages of L. salmonis, and for C. elongatus mobiles. The analyses indicate that significant clustering of lice infections within cages occurs across lice species and stages on both Scottish and Norwegian farms. A Monte-Carlo simulation using two sets of data from Scottish farms with ICC values for adult L. salmonis of 0.35 [0.08-0.73, 95% CI] and for adult C. elongatus of 0.39 [0.16-0.69, 95% CI] were used to illustrate the implications of clustering. The protocols simulated reflect those typically used across a range of countries and production environments in which salmon are currently reared. The findings demonstrate that the "few fish from many cages" approach results in a marked improvement in precision when sampling aquatic one-host parasites in cage-based production systems.

A simulation model to assess herd-level intervention strategies against E. coli O157.

A simulation model of a herd of grazing cattle, which has been developed to provide insight into the infection dynamics of E. coli O157 is described. The spatially explicit model enables the modelling of the infection transmission processes to be realistically addressed under field management conditions. The model is used to explore the efficacy of various potential control strategies in reducing the levels of within-herd infection. These measures include restricting the size of herds, niche engineering, improving housing hygiene and vaccination. While a vaccination strategy remains a hypothetical option, it has the potential to be particularly effective. It is likely that the most successful strategy will involve the implementation of a combination of measures.

Assessing the efficacy of within-animal control strategies against E. coli O157: a simulation study.

A stochastic simulation model was used to assess the efficacy of potential measures to control the levels of Escherichia coli O157 within the bovine host. The model described E. coli O157 population sizes at several sites along the bovine gut and therefore only interventions that operate at an individual animal level could be evaluated. In order to use the model to evaluate the control strategies, it was necessary to make assumptions about how each strategy affected E. coli O157 populations in vivo. The within-animal conditions under these control strategies were modelled by adjusting the growth rates of E. coli O157 at specific sites of interest in the gut, based on these assumptions. The model simulated the population dynamics of an initial dose of E. coli O157 inoculated into an animal in the presence of inhibitory probiotics or antibiotics, bactericidal antibiotics or probiotics, and following fasting. Of the control strategies considered, the use of inhibitory probiotics appeared most promising and continued development of a suitable product is to be encouraged.

A simulation model for the study of the within-animal infection dynamics of E. coli O157.

Escherichia coli 0157 can cause serious illness, even death, in humans. There is some consensus that the main reservoirs of this harmful bacterium are the rumens and intestines of cattle. Hence, a stochastic model of the bovine gut was developed to investigate the in vivo population dynamics of E. coli O157. Because bacterial numbers can reach minimal levels, a stochastic system was considered, with a birth-death process being used to represent bacterial growth and decay dynamics throughout the gastrointestinal tract. Reinfection through ingestion of bacteria present in the environment was allowed to occur and the required clustered distribution of inter-event times was implemented through the use of a random hazard doubly stochastic Poisson process. Due to the inclusion of multiple compartments, a feedback mechanism and an interest in the non-equilibrium dynamics of the process, it was not possible to obtain an analytical representation of the process and therefore, a simulation study was used to obtain results. The within-animal model can be used to explore the efficacy of control measures which act at an individual animal level.