Non-outbreak Conditions Research Articles

Developments in microbiological risk assessment for drinking water.

1. SUMMARYThis paper considers the development of microbiologicalrisk assessment models for pathogenic agents in drinkingwater with particular reference to Cryptosporidium parvum,rotavirus and bovine spongiform encephalopathy (BSE).The available evidence suggests that there is potential forconsiderable variation in exposures to C. parvum oocyststhrough drinking water, during both outbreak and non-outbreak conditions. This spatial/temporal heterogeneityarises both from variation in oocyst densities in the rawwater and fluctuations in the removal efficiencies of drinkingwater treatment. In terms of risk prediction, modelling thevariation in doses ingested by individual drinking waterconsumers is not important if the dose–response curve islinear and the oocysts act independently during infection.Indeed, the total pathogen loading on the population asrepresented by the arithmetic mean exposure is sufficient forrisk prediction for C. parvum, BSE and other agents of lowinfectivity, providing the infecting particles (i.e. oocysts orBSE prions) are known to act independently. However, formore highly infectious agents, such as rotavirus, ignoring1. Summary, 1912. Introduction, 1922.1 Overview of the risk assessment approach, 1923. Pathogen exposures through drinking water, 1923.1 Pathogen exposures under non-outbreak condi-tions, 1933.1.1 Variation in micro-organism counts withinlarge volume samples, 1933.1.2 Effect of treatment on the spatial distribu-tion of micro-organisms, 1933.1.3 Implication for Cryptosporidium exposures todrinking water consumers under non-out-break conditions, 1953.2 A model for Cryptosporidium oocyst concentrationsin drinking water during an outbreak, 1964. Dose–response curves. Estimating the risk to humansfrom ingesting low pathogen doses, 1974.1 Cryptosporidium parvum, 1974.1.1 Experiments with salmonellas in mice suggestthat pathogens act independently and do notco-operate during infection, 1984.1.2 Acquired protective immunity for Cryptospo-ridium parvum, 1994.1.3 Virulence of different strains of Cryptospori-dium parvum, 1994.2 Human rotavirus, 1994.3 Bovine spongiform encephalopathy, 2004.3.1 The human oral ID

Prevention and control of epidemic kerato-conjunctivitis in a teaching eye institute

Purpose To determine if an ongoing infection control program is associated with a reduction in rates of nosocomial outbreaks of epidemic keratoconjunctivitis (EKC) and outbreak morbidity from nosocomial EKC in a large teaching eye institute. Methods The number of nosocomial EKC outbreaks, the number of affected patients, and the total number of patient visits were collected for each year between 1984 and 1997. An infection control program was implemented in 1992. The program included specified methods of patient screening and isolation, handwashing, instrument disinfection, medication distribution, and furlough of infected employees. The program included two levels of intensity of infection control measures, for non-outbreak and outbreak conditions. We compared rates per 100,000 patient visits of nosocomial outbreaks of EKC and affected patients for the 6-year period after the program was implemented, 1992-1997, with corresponding rates for 1984-1991. Results One to three nosocomial outbreaks of EKC occurred annually in the period 1984-1991. After the implementation of the infection control program, no nosocomial outbreaks occurred in three of six years studied. In the pre-infection control years 1984-1991, there were 3.89 outbreaks and 54.09 affected patients per 100,000 visits, respectively. For the post-infection control years 1992-1997, the corresponding rates were 0.54 outbreaks and 5.66 affected patients per 100,000 patient visits. Rates for both outbreaks and affected patients were significantly lower for the post-implementation period (p < 0.005 and p < 0.0005, respectively). Conclusions An ongoing infection control program was associated with decreased rates of nosocomial EKC outbreaks and outbreak morbidity from nosocomial EKC in our institute. Although several reports have described infection control measures that terminated individual outbreaks of nosocomial EKC, this study demonstrates that an ongoing infection control program may preemptively reduce nosocomial EKC outbreaks.

The applicability of available hazard rating systems for mountain pine beetle in lodgepole pine stands of southeastern Wyoming

Five hazard rating systems for Dendroctonusponderosae Hopkins in Pinuscontorta Dougl. stands were compared under nonoutbreak conditions in the Medicine Bow Mountains of southeastern Wyoming. The applicability of these systems, which were designed in other regions of the United States, to P. contorta stands in southeastern Wyoming was investigated. Thirty-two stands in four different age and diameter categories were sampled and rated by each system. Diameter at breast height did not correlate well with phloem width in any of the stands, as implied by the system of Amman and co-workers. A direct phloem width measurement could further refine this system. Periodic growth ratio, used in both the Berryman and Mahoney systems, did not differentiate between fast- and slow-growing trees. Crown competition factor did not positively correlate with increasing diameter at breast height, as implied by the system of Schenk and co-workers. Stand production ranged from 11.1 to 51.0 g wood•m leaf area−2•year−1, applying a modified system based on that designed by Mitchell and co-workers, indicating very high risk in every stand sampled. Further development and validation of hazard rating systems is necessary for improved analysis of risk to P. contorta stands from D. ponderosae in this region.