SEARCH · PubMed Health

Results for “environmental persistence”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources

PubMed2005

Environmental contamination with an epidemic strain of Pseudomonas aeruginosa in a Liverpool cystic fibrosis centre, and study of its survival on dry surfaces.

We conducted an environmental survey in the Liverpool adult cystic fibrosis (CF) centre in order to determine the extent of environmental contamination with an epidemic strain of Pseudomonas aeruginosa that colonizes most CF patients in Liverpool, and to identify possible reservoirs and routes of cross-infection. In addition, we studied the survival of this strain on dry surfaces, compared with that of other CF P. aeruginosa strains, to explore factors that might contribute to its high transmissibility. Samples were collected from staff, patients and the environment (drains, bath tubs, showers, dry surfaces, respiratory equipment and air) in the inpatient ward and outpatient clinic. P. aeruginosa strains were tested using a new polymerase chain reaction amplification assay specific for the Liverpool epidemic strain (LES). LES was isolated from patients' hands, clothes and bed linen. Environmental contamination with LES was only detected in close proximity to colonized patients (external surfaces of their respiratory equipment, and spirometry machine tubing and chair) and was short-lived. No persistent environmental reservoirs were found. LES was detected in the majority of air samples from inside patients' rooms, the ward corridor and the outpatient clinic. Survival of LES on dry surfaces was significantly longer than that for some other strains tested, but not compared with other strains shown not to be transmissible. Improved environmental survival on its own, therefore, cannot explain the high transmissibility of this epidemic strain. Our study suggests that airborne dissemination plays a significant role in patient-to-patient spread of LES, and confirms the need to segregate those patients colonized by epidemic P. aeruginosa strains from all other CF patients.

Adult↗

PubMed2003

The second law of thermodynamics is the first law of psychology: evolutionary developmental psychology and the theory of tandem, coordinated inheritances: comment on Lickliter and Honeycutt (2003).

Organisms inherit a set of environmental regularities as well as genes, and these two inheritances repeatedly encounter each other across generations. This repetition drives natural selection to coordinate the interplay of stably replicated genes with stably persisting environmental regularities, so that this web of interactions produces the reliable development of a functionally organized design. Selection is the only known counterweight to the tendency of physical systems to lose rather than grow functional organization. This means that the individually unique and unpredictable factors in the web of developmental interactions are a disordering threat to normal development. Selection built anti-entropic mechanisms into organisms to orchestrate transactions with environments so that they have some chance of being organization-building and reproduction-enhancing rather than disordering.

Biological Evolution↗

PubMedDate not supplied

Is there a need for systematic blood lead screening in Canadian children?

Neuropsychological effects occurring in young children exposed to low blood lead levels are now better known. This paper reviews the need to systematically screen for blood lead levels compatible with subclinical lead poisoning in young Canadian children. Using standard criteria for judging the appropriateness of this measure, the authors found no evidence to support such a practice in Canada. Case-finding is recommended in clinical settings for children with disorders suggestive of lead poisoning, increased lead absorption or exposure to a potential source of lead. A population survey is also recommended in the presence of a well-documented community environmental lead source. There is a need for common protocols across Canada for evaluating and treating children with blood lead levels compatible with subclinical poisoning. Areas of priority research are: the impact of persistent environmental sources of lead such as old paint and lead in water; defining criteria for selective screening; and methods of cost-effective environmental remediation.

Canada↗

PubMedDate not supplied

Malathion and malaoxon environmental levels used for exposure assessment and risk characterization of aerial applications to residential areas of southern California, 1989-1990.

Between August 1989 and July 1990, California conducted a Mediterranean fruit fly eradication project in southern California which included repeated aerial applications of malathion bait to urban areas where approximately 1.6 million people resided. Concern about the safety of these applications prompted the California Department of Health Services to prepare a risk assessment. The current work presents the estimates of environmental levels of malathion and malaoxon, derived from mass deposition rates during application and monitoring of air. We estimated short and long-term malathion and malaoxon levels on outdoor surfaces, plants, and soils (0.1 and 1.0 cm mixing depth), using a simple first-order exponential decay model and literature half-life values ranging from three to nine days. Direct monitoring data were used to characterize short-term air levels. Average and upper-bound malathion levels immediately following an application were 0.091 microgram/m3 and 0.207 microgram/m3 in air; 22 and 52 mg/m2 on outdoor surfaces; 3.8 and 9.6 micrograms/g in plants; and 1.5 and 3.5 micrograms/g in soil (1 cm mixing depth). Malaoxon levels were 0.039 microgram/m3 and 0.110 microgram/m3 in air; 0.15 and 0.46 mg/m2, 0.03 and 0.09 microgram/g, and 0.01 and 0.03 microgram/g, respectively. Estimates of average and upper-bound levels over the duration of the eradication program were roughly one-third the immediate levels in all media. No field measurements were available for co-products other than malaoxon, for environmental persistence, or for concentrations on surfaces, soil, or plants after repeated applications. Because of limited monitoring data, and the likelihood that similar pest-eradication programs will be conducted, additional studies are warranted to more accurately characterize the environmental fate of malathion and human exposures after aerial application to residential communities.

Animals↗

PubMed2006

Transmissibility of cholera: in vivo-formed biofilms and their relationship to infectivity and persistence in the environment.

The factors that enhance the waterborne spread of bacterial epidemics and sustain the epidemic strain in nature are unclear. Although the epidemic diarrheal disease cholera is known to be transmitted by water contaminated with pathogenic Vibrio cholerae, routine isolation of pathogenic strains from aquatic environments is challenging. Here, we show that conditionally viable environmental cells (CVEC) of pathogenic V. cholerae that resist cultivation by conventional techniques exist in surface water as aggregates (biofilms) of partially dormant cells. Such CVEC can be recovered as fully virulent bacteria by inoculating the water into rabbit intestines. Furthermore, when V. cholerae shed in stools of cholera patients are inoculated in environmental water samples in the laboratory, the cells exhibit characteristics similar to CVEC, suggesting that CVEC are the infectious form of V. cholerae in water and that CVEC in nature may have been derived from human cholera stools. We also observed that stools from cholera patients contain a heterogeneous mixture of biofilm-like aggregates and free-swimming planktonic cells of V. cholerae. Estimation of the relative infectivity of these different forms of V. cholerae cells suggested that the enhanced infectivity of V. cholerae shed in human stools is largely due to the presence of clumps of cells that disperse in vivo, providing a high dose of the pathogen. The results of this study support a model of cholera transmission in which in vivo-formed biofilms contribute to enhanced infectivity and environmental persistence of pathogenic V. cholerae.

Animals↗

PubMed1990

Ecological toxicology and human health effects of heptachlor.

The chlorinated cyclodiene heptachlor was registered in 1952 as an agricultural and domestic insecticide. By early 1984, registration for all purposes, except subterranean termite control and for limited use in the control of fire ants, had been cancelled. This restriction of use arose primarily from concerns over the environmental persistance and bioaccumulation potential of the organochlorine pesticides. Currently, sale of heptachlor has been voluntarily suspended over questions about its carcinogenic potential, and the absence of safe and effective application methods. As a persistent organochlorine pesticide, heptachlor residues are detected in all components of the environment. In historical use, heptachlor was directly applied to terrestrial systems, while air and water were secondarily contaminated via volatilization and land run-off, respectively. Within each environmental compartment, heptachlor undergoes a variety of metabolic and abiotic transformations. In vivo studies indicate that heptachlor epoxide is the predominant metabolite, formed as a product of the mixed-function oxidase system, while 1-hydroxychlordene is the major soil metabolite. For quantification, heptachlor and its metabolites are extracted from air, soil and sediment, water, or biological materials using various organic solvents and analyzed by gas chromatography or thin-layer chromatography. Residue reports comprise most of the literature concerning the effects of heptachlor on the biota. In many such reports, toxic effects cannot be conclusively attributed to heptachlor exposure. Toxicity to organisms seems more dependent on acute exposure, while the chronic effects of low level exposure to heptachlor are poorly defined. Maximal terrestrial residues coincide with temporal and spatial proximity to application; peak residues in aquatic systems on the other hand, correlate to periods of maximum run-off. The lipophilic nature of both heptachlor and heptachlor epoxide results in the potential for significant bioaccumulation in all lipid-type compartments in the environment. The toxic effects of heptachlor are not specific for any one organ system. The liver and the central nervous system are most significantly affected by heptachlor, although effects can also be seen in the reproductive, hematopoietic, immune, and renal systems. An important consideration is the relation of relevant environmental exposure levels to toxicity. The concentrations necessary to elicit results in laboratory experiments do not translate directly to the same results upon environmental exposure, nor do experimental laboratory animal models absolutely equate with native-state organisms or with humans.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2026

Outbreaks of fluconazole-resistant Candida parapsilosis are driven by low-biofilm-producing isolates that emerge under host selection.

Candida parapsilosis is a major human fungal pathogen, with recent global outbreaks driven by fluconazole-resistant (FLCR-Cp) isolates that are difficult to eradicate and associated with poor clinical outcomes. However, the microbial traits enabling persistence of these outbreak lineages remain poorly defined. Here, we show that FLCR-Cp isolates responsible for prolonged, multi-country outbreaks consistently exhibit a striking low-biofilm-producing (LBP) phenotype. Contrary to the prevailing view that robust biofilm formation promotes persistence, LBP strains displayed enhanced stress tolerance, increased cell wall masking, and reduced immune recognition. These traits conferred resistance to neutrophil and macrophage killing and enhanced survival in immune cell-rich organs during systemic infection. Genome-wide transcriptomic profiling revealed extensive metabolic and regulatory rewiring in LBP strains. Whole-genome sequencing (WGS) of a global isolate collection further demonstrated that the LBP phenotype has emerged independently multiple times, supporting convergent evolution under host selection. Functional genomic analyses suggest that biofilm attenuation arises through multigenic changes, and disruption of key biofilm-associated transcriptional regulators enhanced fitness during immune interactions. Together, our findings overturn the assumption that robust biofilm formation drives outbreak persistence and instead identify biofilm attenuation as an adaptive tradeoff that promotes immune evasion and long-term survival. These results redefine our understanding of C. parapsilosis adaptation during healthcare-associated outbreaks and shift attention toward host-driven evolutionary processes than environmental persistence alone.

Biofilms↗

PubMed1996

Improper use of an insecticide at a kindergarten.

In a German kindergarten cockroaches were destroyed by a commercial firm. A preparation containing pyrethrum and its synergist piperonyl butoxide and the organic phosphorus pesticide chlorpyriphos was sprayed. While cleaning the rooms, the staff complained of health effects. Thereupon the kindergarten was closed until further notice, samples were taken by the health authorities for chemical analysis, and an environmental medical evaluation was initiated. The analytical results are presented. The toxicological significance of the employed insecticides, their environmental persistence, and the problems associated with pest control in such institutions are discussed and recommendations given.

Air Pollution, Indoor↗

PubMed2004

Environmental sources of prion transmission in mule deer.

Whether transmission of the chronic wasting disease (CWD) prion among cervids requires direct interaction with infected animals has been unclear. We report that CWD can be transmitted to susceptible animals indirectly, from environments contaminated by excreta or decomposed carcasses. Under experimental conditions, mule deer (Odocoileus hemionus) became infected in two of three paddocks containing naturally infected deer, in two of three paddocks where infected deer carcasses had decomposed in situ =1.8 years earlier, and in one of three paddocks where infected deer had last resided 2.2 years earlier. Indirect transmission and environmental persistence of infectious prions will complicate efforts to control CWD and perhaps other animal prion diseases.

Animals↗

PubMed2005

The potential impact of climate change on infectious diseases of Arctic fauna.

Climate change is already affecting Arctic species including infectious disease agents and greater changes are expected. Some infectious diseases are already increasing but future changes are difficult to predict because of the complexity of host-agent-environment relationships. However mechanisms related to climate change that will influence disease patterns are understood. Warmer temperatures will benefit free living bacteria and parasites whose survival and development is limited by temperature. Warmer temperatures could promote survivability, shorter development rates and transmission. Insects such as mosquitoes and ticks that transmit disease agents may also benefit from climate change as well as the diseases they spread. Climate change will have significant impacts on biodiversity. Disease agents of species that benefit from warming will likely become more prevalent. Host species stressed by changing environmental conditions may be more vulnerable to disease agents. Warming could lead to increased agriculture and other economic opportunities in the Arctic bringing people, domestic food animals, pets and invasive species and their disease agents into Northern regions. Climate warming may also favor the release of persistent environmental pollutants some of which can affect the immune system and may favor increased rates of some diseases.

Acclimatization↗

PubMed2004

Occupational exposure associated with reproductive dysfunction.

Evidence suggestive of harmful effects of occupational exposure on the reproductive system and related outcomes has gradually accumulated in recent decades, and is further compounded by persistent environmental endocrine disruptive chemicals. These chemicals have been found to interfere with the function of the endocrine system, which is responsible for growth, sexual development and many other essential physiological functions. A number of occupations are being reported to be associated with reproductive dysfunction in males as well as in females. Generally, occupations involving the manufacture/or application of some of the persistent chemicals that are not easily degradable as well as bio-accumulative chemicals, occupations involving intensive exposure to heat and radiation, occupations involving the use of toxic solvents as well as toxic fumes are reported to be associated with reproductive dysfunction. Occupational exposure of males to various persistent chemicals have been reported to have male mediated adverse reproductive outcomes in the form of abortion, reduction in fertility etc. with inconclusive or limited evidence. Nevertheless, there is a need for more well designed studies in order to implicate any individual chemical having such effects as in most occupations workers are exposed to raw, intermediate and finished products and there are also several confounding factors associated with lifestyles responsible for reproductive dysfunction. There is an urgent need to look at indiscriminate use of persistent chemicals especially pesticides and persistent organic pollutants (POP's) as these chemicals enter the food chain also and could be potential for exposure during the critical period of development. It is also necessary to impart information, and to educate about the safe use of these chemicals, as a very sensitive reproduction issue is involved with exposure to these chemicals. Occupational exposures often are higher than environmental exposures, so that epidemiological studies should be conducted on these chemicals, on a priority basis, which are reported to have adverse effects on reproduction in the experimental system.

Agricultural Workers' Diseases↗

PubMed1992

A source inventory and budget for chlorinated dioxins and furans in the United Kingdom environment.

Polychlorinated dibenzo-p-dioxins (PCDDs) and -furans (PCDFs) are ubiquitous in the environment. This paper estimates the present UK environmental loading of PCDD/Fs in soils, vegetation, air, water and sediments. Greater than 95% of the estimated total PCDD/F loading of 5.7 t in the UK environment is present in surface soils. Annual emissions from known primary sources of PCDDs and PCDFs are estimated. The most important of these include: municipal waste incinerator stack emissions (10.9 kg sigma PCDD/F per annum); industrial (7.7 kg/year) and domestic (5.1 kg/year) combustion of coal; clinical waste incinerators (1.7 kg/year); volatilisation from chlorophenol-treated substrates (1.7 kg/year) and combustion of leaded petrol by motor vehicles (0.7 kg/year). These sources are generally easy to define and reasonably reliable national estimates can be obtained. More difficult to quantify are secondary releases from the large UK stock of pentachlorophenol (PCP) and PCP-treated products, which may represent quantitatively one of the most important sources of total PCDD/Fs to the environment. Estimates of homologue-specific emissions indicate that combustion processes represent a far more significant source of tetra and penta CDD/Fs than do chlorophenols, which in turn constitute a greater source of hepta- and octachlorinated congeners. Direct emission of PCDD/Fs into the atmosphere from combustion processes facilitates their atmospheric transport to remote locations. This, coupled with the diffuse nature of combustion processes, means that the effects of PCDD/F contamination originating from anthropogenic combustion are more widespread than those from the use and disposal of chlorophenols. Contamination from chlorophenols will be more localised, owing to the insignificance of direct atmospheric release pathways for this source. Although there is reasonable agreement between the estimated current annual flux and the present UK environmental loading of PCDDs and PCDFs, a large discrepancy exists between the sum of the annual contributions from primary sources and this annual flux. Whilst the existence of an as yet unidentified source or sources or gross underestimates of known sources cannot be excluded, it is proposed that much of this discrepancy may be accounted for by secondary releases from the use and disposal of chlorophenols and the long-range transport, continued remobilisation and subsequent redeposition of PCDDs and PCDFs already present in the environment. Despite limited evidence for a modest decline in levels of PCDDs and PCDFs in some environmental compartments over the last 20 years, the environmental persistence of these chemicals means that they will remain in the UK environment for the foreseeable future despite recent action to curb primary emissions.

Air Pollutants↗

PubMed2000

Biological Monitoring of Pesticide Exposure: a review. Introduction.

Pesticides are used worldwide in agriculture, industry, public health and for domestic applications: as a consequence, a great part of the population may be exposed to these compounds. In spite of this extensive use, knowledge on the health risks associated with prolonged exposure is rather poor, and major uncertainties still exist. Epidemiological observations in man have so far produced little conclusive information, mainly because of weaknesses in exposure assessment. Therefore, information on the type and levels of exposure is fundamental in order to better understand and characterize risk to human health. Exposure assessment can be carried out via measurement of environmental concentrations, as well as via determination of the chemical or its metabolites in body tissues (biological monitoring). Besides indices of internal dose, biological monitoring also includes measurements of early effects attributable to interaction between the chemical agent and the human body. Biological monitoring has the advantage, over environmental monitoring, of determining the dose actually absorbed via any possible route: differences in absorption can be taken into account. whether they are due to biological variability or to use of protective equipment. When, in some cases, a combination of occupational and non-occupational exposure occurs, this also can be taken into consideration by biological monitoring. Few reference documents have been published on biological monitoring of pesticides. For this reason, the Office of Occupational Health of the World Health Organization gave ICPS a mandate to prepare a monograph specifically addressed to reviewing methods for biological monitoring of pesticide exposure. This review is based on more than 300 studies published over the period 1980-1999. For the most representative chemical classes, the available biological exposure indices are reported. Both indices of internal dose and. when available, of early effects are discussed. The reported tests were used to monitor exposure of pesticide applicators in agriculture and public health, manufacturing and formulating workers. subjects poisoned after accidental exposure or attempted suicide, volunteers involved in pharmacokinetic studies, as well as sub-groups of the general population exposed to environmentally persistent pesticides. Single chapters deal with organophosphorus insecticides, carbamate pesticides, dithiocarbamates, phenoxyacids, quaternary ammonium compounds. coumarin rodenticides, synthetic pyrethroids, organochlorine pesticides, chlorotriazines, and pentachlorophenol.

Animals↗

PubMedDate not supplied

Environmental contaminants in human milk.

Environmental contaminants can be stored in the mother's body or can be transiently present from current diet, occupational exposures or personal habits. These chemicals can be transferred prenatally to the developing fetus or postnatally from breast milk to the nursing infant. Exposures through breast milk can be substantial, especially when the mother has significant ongoing exposures or has accumulated an unusually high body burden of persistent chemicals. Several studies demonstrate that organochlorines (OCs) acquired from breast milk elevate a child's body burden for several years. The decline of persistent OC residues in Western countries suggests that these exposures through breast milk will also diminish. Heavy metals such as lead and mercury are also present in milk, but the pharmacokinetics are quite different from OCs. Less persistent environmental agents, including solvents, polycyclic aromatic hydrocarbons, certain pesticides, and nicotine, can also be detected in milk. There is little information on currently used pesticides and other more recently identified environmental agents for which exposures are common today. Epidemiologic research has established that pre- and postnatal exposures to environmental contaminants including lead and OCs are associated with developmental deficits in early childhood. Therefore, characterization of these contaminants in breast milk can add to our knowledge of potential environmental exposures among children.

Adult↗

PubMed1997

Dioxins and the Ah receptor: probes to uncover processes in neuroendocrine development.

The developing neuroendocrine system is thought to be a sensitive target for a number of environmental chemicals. Many of these chemicals act, not by directly damaging macromolecules but through the inappropriate modulation of normal cellular processes that regulate cell growth and differentiation patterns. As our knowledge of the specific hormones and signaling pathways involving in these functions has advanced, so has our understanding that these chemicals may act by a number of different molecular mechanisms. The dioxin-like compounds are persistent environmental contaminants. The findings that they affect cell proliferation and differentiation, are tumor promoters, and are potent immuno-, developmental, and reproductive toxicants by mechanisms not dependent on cytotoxicity, are consistent with the hypothesis that these compounds act by modulating normal cell and tissue growth processes. Furthermore, findings in exposed experimental animals and humans suggest that the developing neuroendocrine system is a sensitive target for these chemicals. All evidence to data indicates that these compounds produce their biological and toxicology affects by binding to a gene regulatory protein, the Ah receptor, whose normal function has not been clearly delineated and whose normal endogenous ligand has not been identified. Yet data on the biochemistry and molecular biology of this transcription factor indicates that well regulated and conserved pathways exist for it to mediate the transduction of biochemical signals for the control of a number of hormones and growth factors. These and other data provide evidence to suggest that the Ah receptor may be necessary for the normal development of many tissues including those in the neuroendocrine system. Further research is necessary to understand if and how it may function in this system, what the normal endogenous ligand is, and how perturbations in its activity may affect normal development processes.

Animals↗

PubMed2004

Modelling the fate of persistent organic pollutants in Europe: parameterisation of a gridded distribution model.

A regionally segmented multimedia fate model for the European continent is described together with an illustrative steady-state case study examining the fate of gamma-HCH (lindane) based on 1998 emission data. The study builds on the regionally segmented BETR North America model structure and describes the regional segmentation and parameterisation for Europe. The European continent is described by a 5 degrees x5 degrees grid, leading to 50 regions together with four perimetric boxes representing regions buffering the European environment. Each zone comprises seven compartments including; upper and lower atmosphere, soil, vegetation, fresh water and sediment and coastal water. Inter-regions flows of air and water are described, exploiting information originating from GIS databases and other georeferenced data. The model is primarily designed to describe the fate of Persistent Organic Pollutants (POPs) within the European environment by examining chemical partitioning and degradation in each region, and inter-region transport either under steady-state conditions or fully dynamically. A test case scenario is presented which examines the fate of estimated spatially resolved atmospheric emissions of lindane throughout Europe within the lower atmosphere and surface soil compartments. In accordance with the predominant wind direction in Europe, the model predicts high concentrations close to the major sources as well as towards Central and Northeast regions. Elevated soil concentrations in Scandinavian soils provide further evidence of the potential of increased scavenging by forests and subsequent accumulation by organic-rich terrestrial surfaces. Initial model predictions have revealed a factor of 5-10 underestimation of lindane concentrations in the atmosphere. This is explained by an underestimation of source strength and/or an underestimation of European background levels. The model presented can further be used to predict deposition fluxes and chemical inventories, and it can also be adapted to provide characteristic travel distances and overall environmental persistence, which can be compared with other long-range transport prediction methods.

Climate↗

PubMed1995

Evolution of biological regulation networks under complex environmental constraints.

This work investigates the influence of environmental inducers on the organization of cell regulation networks, using a connectionist approach. Protein interactions are modeled by an asymmetrical recurrent network, the units of which take continuous values. In contrast to classical models, we explicitly introduce a genome to encode the architecture of the system. This feature enables us to introduce an evolution model, in which a genetic algorithm that mimics the effects of evolution on proteins mutual interactions is used. We assume an efficient system to respond to persistent environmental stimuli, independently of their amplitude. Results are presented that show a structuration of the network with the emergence of specialized hierarchal structures. These structures seem to drive the system at the edge of chaos, so that it can present adapted responses to significant environmental changes.

Algorithms↗

PubMed2004

Molecular Subtyping and Tracking of Listeria monocytogenes in Latin-Style Fresh-Cheese Processing Plants.

Latin-style fresh cheeses, which have been linked to at least 2 human listeriosis outbreaks in the United States, are considered to be high-risk foods for Listeria monocytogenes contamination. We evaluated L. monocytogenes contamination patterns in 3 Latin-style fresh-cheese processing plants to gain a better understanding of L. monocytogenes contamination sources in the manufacture of these cheeses. Over a 6-mo period, 246 environmental samples were collected and analyzed for L. monocytogenes using both the Food and Drug Administration (FDA) method and the Biosynth L. monocytogenes detection system (LMDS). Finished cheese samples from the same plants (n = 111) were also analyzed by the FDA method, which was modified to include L. monocytogenes plating medium (LMPM) and the L. monocytogenes confirmatory plating medium (LMCM) used in the LMDS method. Listeria monocytogenes was detected in 6.3% of cheese and 11.0% of environmental samples. Crates, drains, and floor samples showed the highest contamination rates, with 55.6, 30.0, and 20.6% L. monocytogenes positive samples, respectively. Finished products and food contact surfaces were positive in only one plant. The FDA method showed a higher sensitivity than the LMDS method for detection of L. monocytogenes from environmental samples. The addition of LMPM and LMCM media did not further enhance the performance of the FDA method for L. monocytogenes detection from finished products. Molecular subtyping (PCR-based allelic analysis of the virulence genes actA and hly and automated ribotyping) was used to track contamination patterns. Ribotype DUP-1044A, which had previously been linked to a 1998 multistate human listeriosis outbreak in the United States, was the most commonly identified subtype (20/36 isolates) and was isolated from 2 plants. This ribotype was persistent and widespread in one factory, where it was also responsible for the contamination of finished products. We hypothesize that this ribotype may represent a clonal group with a specific ability to persist in food processing environments. While previous listeriosis outbreaks were linked to Latin-style fresh cheeses made from unpasteurized milk, the presence of this organism in pasteurized cheese products illustrates that persistent environmental contamination also represents an important source of finished product contamination.

Cheese↗