How reliable are test results from 17 laboratories on the basis of EN 1500 for a hand rub based on 80% (w/w)?

INTRODUCTION

A ring trial organized by the Association of Applied Hygiene (VAH) on the bactericidal efficacy of an ethanol-based hand rub was carried out in 17 laboratories according to EN 1500 with the aim of describing the variability of test results and fulfilment of the methodological acceptance criteria.

METHOD

As a test product, a hand rub based on 80% ethanol (w/w) was tested in comparison with the reference alcohol (60% iso-propanol, v/v) in a crossover design. After pre-washing and contamination following the norm, hands were treated either with the reference alcohol (2 × 3 mL for 2 × 30 s) or the test product (3 mL in 30 s). Post-decontamination values were determined immediately after the rub-in period. Validated neutralizers were used. The arithmetic means of all individual log10 pre-values, post-values and reduction values were calculated per laboratory. Non-inferiority was assumed when the Hodges-Lehmann 97.5% confidence limit was <0.6 in comparison with the reference. A z-score was calculated to determine the laboratory performance.

RESULTS

Two laboratories did not meet the acceptance criteria and were excluded from the analysis. The bactericidal efficacy of the test product was non-inferior to the reference product in four laboratories and not non-inferior in 11 laboratories. The z-score for the Hodges-Lehmann 97.5% confidence limit indicated a satisfactory performance in all laboratories.

CONCLUSION

We consider the EN 1500 test method to be robust in terms of the variability of test results. For products of borderline efficacy, the evaluation should be based on more than one test.

Failure of sodium hypochlorite to meet the EN 1500 efficacy requirement for hygienic hand disinfection

This study evaluated the bactericidal efficacy of two alternative hand antiseptics, based on sodium hypochlorite or sodium hypochlorite and hypochlorous acid, compared with isopropanol on the hands of volunteers artificially contaminated with Escherichia coli using EN 1500. The reference alcohol was applied according to the norm, and the study formulations were used as in common practice (3 mL for 30 s). The products showed mean log₁₀ reductions of 1.63 and 1.89, both of which were inferior to the reference treatment (4.78). Due to the failure to achieve sufficient bactericidal efficacy within 30 s, sodium hypochlorite (0.05-0.06%) should not be considered for hand disinfection.

Interlaboratory reproducibility of a test method following 4-field test methodology to evaluate the susceptibility of Clostridium difficile spores

BACKGROUND

Sporicidal surface disinfection is recommended to control transmission of Clostridium difficile in healthcare facilities. EN 17126 provides a method to determine the sporicidal activity in suspension and has been approved as a European standard. In addition, a sporicidal surface test has been proposed.

AIM

To determine the interlaboratory reproducibility of a test method for evaluating the susceptibility of a C. difficile spore preparation to a biocidal formulation following the 4-field test (EN 16615 methodology).

METHODS

Nine laboratories participated. C. difficile NCTC 13366 spores were used. Glutaraldehyde (1% and 6%; 15 min) and peracetic acid (PAA; 0.01% and 0.04%; 15 min) were used to determine the spores' susceptibility in suspension in triplicate.

FINDINGS

One-percent glutaraldehyde revealed a mean decimal log₁₀ reduction of 1.03 with variable results in the nine laboratories (0.37-1.49) and a reproducibility of 0.38. The effect of 6% glutaraldehyde was stronger (mean: 2.05; range: 0.96-4.29; reproducibility: 0.86). PAA revealed similar results. An exemplary biocidal formulation based on 5% PAA was used at 0.5% (non-effective concentration) and 4% (effective concentration) to determine the sporicidal efficacy (4-field test) under clean conditions in triplicate with a contact time of 15 min. When used at 0.5% it demonstrated an overall log₁₀ reduction of 2.68 (range: 2.35-3.57) and at 4% of 4.61 (range: 3.82-5.71). The residual contamination on the three primarily uncontaminated test fields was <50 cfu/25 cm² in one out of nine laboratories (0.5%) and in seven out of nine laboratories (4%).

CONCLUSION

The interlaboratory reproducibility seems to be robust.

Isopropanol at 60% and at 70% are effective against 'isopropanol-tolerant' Enterococcus faecium

The bactericidal activity of isopropanol was determined against Enterococcus faecium ATCC 6057, ST 796 (isopropanol-tolerant strain) and Enterococcus hirae ATCC 10541 (EN 13727). Isopropanol at 60% and 70% were effective (≥5.38 log₁₀-reduction) in 15 s against all strains but 23% isopropanol was not (<0.99 log₁₀-reduction in ≤15 min). Isopropanol at 70% was tested against E. faecium in the four-field test. Eight millilitres was not effective enough in 1 min (<5 log₁₀-reduction), whilst 16 mL was effective (≥5.85 log₁₀-reduction). Healthcare workers can be reassured that 60% and 70% isopropanol with an appropriate volume are effective against E. faecium.

Analysis of the oligomeric state and transactivation potential of TAp73α

The proteins p73 and p63 are members of the p53 protein family and are involved in important developmental processes. Their high sequence identity with the tumor suppressor p53 has suggested that they act as tumor suppressors as well. While p63 has a crucial role in the maintenance of epithelial stem cells and in the quality control of oocytes without a clear role as a tumor suppressor, p73's tumor suppressor activity is well documented. In a recent study we have shown that the transcriptional activity of TAp63α, the isoform responsible for the quality control in oocytes, is regulated by its oligomeric state. The protein forms an inactive, dimeric and compact conformation in resting oocytes, while the detection of DNA damage leads to the formation of an active, tetrameric and open conformation. p73 shows a high sequence identity to p63, including those domains that are crucial in stabilizing its inactive state, thus suggesting that p73's activity might be regulated by its oligomeric state as well. Here, we have investigated the oligomeric state of TAp73α by size exclusion chromatography and detailed domain interaction mapping, and show that in contrast to p63, TAp73α is a constitutive open tetramer. However, its transactivation potential depends on the cellular background and the promoter context. These results imply that the regulation of p73's transcriptional activity might be more closely related to p53 than to p63.

Detection of Helicobacter pylori in biofilms by real-time PCR

Helicobacter pylori is a cause of peptic ulcer disease and a causative agent of gastric cancer. Currently, a possible waterborne route of transmission or a possible survival in drinking water biofilms is discussed. H. pylori, like many other bacterial strains, has the ability to enter the viable but nonculturable state (vbnc) in case of unfavorable conditions. Therefore it is necessary to develop new analysis tools for vbnc bacteria. We established a fast and reliable method to detect H. pylori in drinking water biofilms by quantitative real-time PCR which makes it redundant to use difficult cultivation methods for nonculturable bacteria. With this method it was possible to identify water biofilms as a niche for H. pylori. The real-time PCR analysis targets the ureA subunit of the Helicobacter pylori urea gene which showed high specificity and sensitivity. The quantitative real-time PCR was used to detect H. pylori in biofilms of different age, unspiked and spiked with predetermined levels of cells. The drinking water biofilms were generated in a silicone-tube model. The DNA-sequences for probe and primers showed no cross-homologies to other related bacteria and it was possible to detect less than 10 genomic units of H. pylori. This novel method is a useful tool for a fast screening of drinking water biofilms for H. pylori. The results suggest that drinking water biofilms may act as a reservoir for H. pylori which raises new concerns about the role of biofilms as vectors for pathogens like Helicobacter pylori.

[Risk of infection in the home environment. Plea for a new risk assessment]

Within the last two decades risks posed by infectious diseases outside of hospitals and nursing homes had no high significance in the public perception. The home environment is regarded as a save shelter from infectious risks. In the mean time there have been dramatic socio-demographic, health policy and technological changes which have increased infectious risks outside medical facilities. In Germany up to 1.4 million people with multiple morbidities are nursed at home. Technological changes with the aim to protect the environment, like reduction of water temperature and water volumes in washing processes has lowered the efficacy to control pathogens. Thus it is time to revise the process of risk assessment in which not only aspects of environmental protection but also those of health protection must be taken into account. The article gives an overview of new risks and epidemiological changes and discusses the necessity of a new risk assessment and risk management approach which hopefully will lead to a changing paradigm.

Wasser als Infektionsquelle in medizinischen Einrichtungen, Prävention und Kontrolle

New epidemiological and microbiological investigations using molecular typing methods to link patient and environmental strains demonstrate a strong association between water-borne pathogens and nosocomial infections. Avoiding patient exposure to these pathogens results in a decreased incidence of water-borne nosocomial infections. There remains a tremendous potential to reduce hospital acquired infections previously viewed as inevitable and unavoidable through intervention and preventive measures. The characteristics of water application in health care facilities, the vulnerability of patients, the spectrum of relevant pathogens and their ecologic aspects, legal issues and important measures for prevention and control are discussed.

Process-independent quantitative assessment of residual biological contamination of medical devices reprocessed in washer-disinfectors

A method based on measuring a soil-induced fluorescence intensity response of 1,8-anilinonaphthalene sulfonate at two fixed wavelengths (460 and 510 nm) was used for determining residual contamination on test soil carriers simulating medical devices after passage through a hospital washer-disinfector. The fluorescence response can be satisfactorily calibrated to soil levels as low as approximately 1 microg/L. Practical tests were performed in two hospitals with washer-disinfectors of 3 types and with several chemical or enzymic cleansers-disinfectants. In combination with the previously developed system of standardized test soil carriers simulating both easily and poorly accessible parts of soiled medical devices, the liver-lactose-oil test soil and an efficient sonication procedure for stripping the residual soil off the carriers, this soil detection method permits the detection of very low contamination levels.

Prevention and control of health care-associated waterborne infections in health care facilities

The current article is a review of the public health risks attributable to waterborne pathogens in health care. The consequences of health care-associated infections (HAIs) are discussed. Not only are Legionella spp involved in HAIs, but also Pseudomonas aeruginosa, other gram-negative microorganisms, fungi, and amoeba-associated bacteria. This is particularly noteworthy among immunocompromised patients. New prevention strategies and control measures brought about through advanced planning, facility remodelling and reconstruction, disinfection, and filtration have resulted in a significant reduction of the incidence of waterborne HAIs. The positive consequences of a comprehensive multibarrier approach including prevention and control programs in health care facilities are discussed. Environmental cultures are now integrated within the infection control program of some European countries. In high-risk areas, the application of disposable sterile point-of-use filters for faucets and shower heads appears to be the practice of choice to efficiently control waterborne pathogens and to prevent infections.

Household cleaning and surface disinfection: new insights and strategies

Recently, new insights into the persistence of pathogens, their transfer from inanimate surfaces to humans and the risk of contamination and dissemination of pathogens by detergents have been gained. Furthermore, new experimental data on the interruption of chains of infection by disinfectants as well as results of outbreak-control studies are now available. Hence it has become necessary to reassess the potential benefits using disinfectants to prevent and control nosocomial infections. Based on the new findings and in view of the increasing incidence of nosocomial infections and antibiotic resistances, the German Robert-Koch-Institut has issued completely revised recommendations on Household Cleaning and Surface Disinfection. With respect to these recommendations we developed a new test method, which allows comparison of the efficacy of disinfection in reducing the microbial loads and their dissemination with that of cleaning procedures under practical conditions. In a multi-factor approach, mechanical properties (wet mop technique), utensils (different mop materials) and active agents (disinfectant, detergent) were taken into consideration. We found that under the given conditions, dissemination of the test organism Staphylococcus aureus did not take place when using aldehydes and peroxides, it did take place, however, when water, surfactants, and the disinfectants glycol derivatives, quaternary ammonium compounds and alkylamines were used.

Detection and differentiation of in vitro-spiked bacteria by real-time PCR and melting-curve analysis

We introduce a consensus real-time PCR protocol for the detection of bacterial DNA from laboratory-prepared specimens such as water, urine, and plasma. This prototype detection system enables an exact Gram stain classification and, in particular, screening for specific species of 17 intensive care unit-relevant bacteria by means of fluorescence hybridization probes and melting-curve analysis in a one-run experiment. One strain of every species was tested at a final density of 10(6) CFU/ml. All bacteria examined except Staphylococcus aureus and Staphylococcus epidermidis could be differentiated successfully; S. aureus and S. epidermidis could only be classified as "Staphylococcus species." The hands-on time for preparation of the DNA, performance of the PCR, and evaluation of the PCR results was less than 4 h. Nevertheless, this prototype detection system requires more clinical validation.

Standardized system for quantifying residual dirt on medical appliances cleansed in hospital washers--disinfectors: dirt detection by different methods

An easy-to construct, easy-to-operate standardized system was developed for determining the residual biological contamination of surgical instruments, endoscopes and other medical appliances subjected to hospital cleansing and/or disinfection. It consists of standard-sized pieces of glass, metal or endoscope plastic--dirt carriers--either bare or enclosed in truncated Eppendorf caps to simulate hard-to-access conditions. The surface of the carriers is covered with model dirt simulating biological contamination and the carriers are then affixed to sturdy metal holders. Conventional model dirt were found to peel or flake off the carrier surface, lowering the precision of residual soil determination. A newly developed model dirt consisting of liver mash, lactose and sunflower oil and exhibiting low tendency to peel off surfaces was therefore used. The whole setup was subjected to chemical or enzymic cleansing programs at elevated temperature in hospital washer-disinfectors of two types, and the residual dirt after cleansing was determined by three methods. The method using toxicant-doped dirt that quenches the luminescence of an indicator bacterium Photobacterium phosphoreum gave satisfactory data under laboratory conditions but with hospital-washed samples it exhibited excessive fluctuations caused by bacterium--dirt interactions and by physical influences. Both other methods gave better results but displayed some process sensitivity. The luciferin-luciferase-based ATP bioluminescence assay sometimes gave low or even negative dirt level values and showed a low effect of reduced dirt accessibility on cleansing of metal carriers. The Bradford protein assay showed about equal cleansing efficiency for both easily and poorly accessible carriers after enzymic cleansing. Our system can be used for determining low levels of residual contamination of medical appliances after cleansing/disinfection and assessing the efficiency of commercial washer-disinfectors; its efficiency can be further increased by using a cleansing process-insensitive method for soil detection and quantification.

Monitoring the kinetics and performance of yeast membrane ABC transporters by diS-C3(3) fluorescence

Kinetic features (initial start-up phase, drug pumping velocity and efficiency as dependent on drug concentration and growth phase) of yeast plasma membrane multidrug resistance ABC pumps were studied by monitoring the uptake of the fluorescent potentiometric dye diS-C3(3), which has been found to be expelled from the cells by these pumps. The monitoring was done with Saccharomyces cerevisiae mutants AD1-8 and AD1-3 deleted in different ABC pumps, and in their pump-competent parent strain US50-18C overexpressing transcriptional activators Pdr1p and Pdr3p. On addition to the cells, diS-C3(3) is expelled by the Pdr5p, Yor1p and Snq2p pumps with overlapping substrate specificity. The pump action can be assessed as a difference between the dye uptake curve for pump-competent and pump-deleted cells. The pump-mediated dye efflux, which shows an initial lag of various lengths, maintains a certain residual intracellular dye level. In the absence of external glucose the dye efflux ability of the pumps depends on the growth phase; late exponential and stationary cells can maintain the export for tens of minutes, whereas exponential cells keep up the pump action for limited time periods. This may reflect an insufficient number of pump molecules in the membrane or an effect of insufficient pump energization from endogenous sources. This effect is not mediated by changes in membrane potential because lowered membrane potential caused by inhibition of the plasma membrane H+-ATPase does not affect the pump action.

Microbial load of drinking water reservoir tributaries during extreme rainfall and runoff

Hygienic and microbiological examinations of watercourses are usually not carried out during heavy rainfall and runoff events. After rainfall or snowmelt, there are often massive increases in turbidity in flooding creeks in mountain ranges, which are frequently interpreted as an indication of microbial contamination. The aim of this study was to quantify the microbial loads of watercourses during such runoff events and to compare these loads with loads occurring during regular conditions. In a 14-month monitoring period we investigated the microbial loads of three tributaries of different drinking water reservoirs. A total of 99 water samples were taken under different runoff conditions and analyzed to determine physical, chemical, bacterial, and parasitic parameters. Thirty-two water samples were considered event samples during nine measuring series. The criteria for events, based on duration and intensity of precipitation, water depth gauge measurements, and dynamics, had been fixed before the investigation for each creek individually. Of the physical and chemical parameters examined, only the turbidity, pH, and nitrate values differed clearly from the values obtained for regular samples. Most of the bacteriological parameters investigated (colony, Escherichia coli, coliform, fecal streptococcal, and Clostridium perfringens counts) increased considerably during extreme runoff events. If relevant sources of parasitic contamination occurred in catchment areas, the concentrations of Giardia and Cryptosporidium rose significantly during events. The results show that substantial shares of the total microbial loads in watercourses and in drinking water reservoirs result from rainfall and extreme runoff events. Consequently, regular samples are considered inadequate for representing the microbial contamination of watercourse systems. The procedures for raw water surveillance in the context of multiple-barrier protection and risk assessment ought to include sampling during extreme runoff situations.

The higher disinfectant resistance of nosocomial isolates of Klebsiella oxytoca: how reliable are indicator organisms in disinfectant testing?

The Children's Clinic in Giessen, Germany recently reported several severe infections with Klebsiella oxytoca resulting in deaths of two neonates. The putative source of the infections was a contaminated infusion solution. The resistance to disinfectant of the K. oxytoca isolates was investigated in three independent laboratories and was indeed found to be significantly increased. Comparative tests with standard strains of K. oxytoca and other recommended bacterial surrogates showed the disinfection procedures used were fully effective. The higher resistance of the nosocomial isolates may have developed due to improper handling and storage of the cleaning utensils. This report describes the events and draws conclusions concerning the use of disinfectants, the treatment of cleaning utensils, the reliability of procedures for testing disinfectants, and suggests additional measures.

Serial [18F] fluorodeoxyglucose positron emission tomography after human neuronal implantation for stroke

OBJECTIVE

There is no known effective treatment for chronic stroke. In this report, we used positron emission tomography (PET) with [18F]fluorodeoxyglucose (FDG) to map the metabolic brain response to neuronal cell implantation in the first human neuroimplantation trial for stroke.

METHODS

Twelve patients (nine men, three women; mean age +/- standard deviation, 60.8+/-8.3 yr) with chronic basal ganglia infarction and persistent motor deficit underwent FDG PET within 1 week before and 6 and 12 months after stereotactic implantation of human neuronal cells. Serial neurological evaluations during a 52-week postoperative period included the National Institutes of Health stroke scale and the European stroke scale.

RESULTS

Alterations in glucose metabolic activity in the stroke and surrounding tissue at 6 and 12 months after implantation correlated positively with motor performance measures.

CONCLUSION

FDG PET performed as part of an initial open-label human trial of implanted LBS-Neurons (Layton BioScience, Sunnyvale, CA) for chronic stroke demonstrates a relationship between relative regional metabolic changes and clinical performance measures. These preliminary findings suggest improved local cellular function or engraftment of implanted cells in some patients.

Disinfectant activity against different morphological forms of Helicobacter pylori: first results

The pathogenic bacterium Helicobacter pylori, which has infected more than one-half of the world's human population, exists in two morphological forms; the viable helical form and the disputed viable-but-not-culturable coccoid form. Infection by the helical form proceeds through the oral-oral route, while that by the coccoid form, if possible at all, is by the faecal-oral and/or the oral-oral route. The present pilot study addresses the question of disinfectant efficacy against both forms of the bacterium.

Greater Cincinnati/Northern Kentucky Stroke Study: volume of first-ever ischemic stroke among blacks in a population-based study

BACKGROUND AND PURPOSE

The volume of ischemic stroke on CT scans has been studied in a standardized fashion in acute stroke therapy trials with median volumes between 10.5 to 55 cm(3). The volume of first-ever ischemic stroke in the population is not known.

METHODS

The first phase of the population-based Greater Cincinnati/Northern Kentucky Stroke Study identified all ischemic strokes occurring in blacks in the greater Cincinnati region between January and June of 1993. The patients in this phase of the study who had a first-ever ischemic clinical stroke were identified, and the volume of ischemic stroke was measured.

RESULTS

There were 257 verified clinical cases of ischemic stroke, of which 181 had a first-ever ischemic infarct. Imaging was available for 150 of these patients, and 79 had an infarct on the CT or MRI study that was definitely or possibly related to the clinical symptoms. For these patients, volumetric measurements were performed by means of the modified ellipsoid method. The median volume of first-ever ischemic stroke for the 79 patients was 2.5 cm(3) (interquartile range, 0.5 to 8.8 cm(3)). There was a significant relation between location of lesion and infarct size (P<0.001) and between volume and mechanism of stroke (P=0.001).

CONCLUSIONS

The volume of first-ever ischemic stroke among blacks in our population-based study is smaller than has been previously reported in acute stroke therapy trials. The large proportion of small, mild strokes in blacks may be an important reason for the low percentage of patients who meet the inclusion criteria for tissue plasminogen activator. Further study is necessary to see if these results are generalizable to a multiracial population.

Transplantation of cultured human neuronal cells for patients with stroke

Transplantation of cultured neuronal cells is safe in animal models and improves motor and cognitive deficits in rats with stroke. The authors studied the safety and feasibility of human neuronal cellular transplantation in patients with basal ganglia stroke and fixed motor deficits, including 12 patients (aged 44 to 75 years) with an infarct 6 months to 6 years previously (stable for at least 2 months). Serial evaluations (12 to 18 months) showed no adverse cell-related serologic or imaging-defined effects. The total European Stroke Scale score improved in six patients (3 to 10 points), with a mean improvement 2.9 points in all patients (p = 0. 046). Six of 11 PET scans at 6 months showed improved fluorodeoxyglucose uptake at the implant site. Neuronal transplantation is feasible in patients with motor infarction.

Incidence rates of first-ever ischemic stroke subtypes among blacks: a population-based study

BACKGROUND AND PURPOSE

The aim of this study was to determine the incidence rates of ischemic stroke subtypes among blacks.

METHODS

Hospitalized and autopsied cases of stroke and transient ischemic attack among the 187 000 blacks in the 5-county region of greater Cincinnati/northern Kentucky From January 1, 1993, through June 30, 1993, were identified. Incidence rates were age- and sex-adjusted to the 1990 US population. Subtype classification was performed after extensive review of all available imaging, laboratory data, clinical information, and past medical history. Case-control comparisons of risk factors were made with age-, race-, and sex-matched control subjects.

RESULTS

Annual incidence rates per 100 000 for first-ever ischemic stroke subtypes among blacks were as follows: uncertain cause, 103 (95% confidence interval [CI], 80 to 126); cardioembolic, 56 (95% CI, 40 to 73); small-vessel infarct, 52 (95% CI, 36 to 68); large vessel, 17 (95% CI, 8 to 26); and other causes, 17 (95% CI, 9 to 26). Of the patients diagnosed with an infarct of uncertain cause, 31% underwent echocardiography, 45% underwent carotid ultrasound, and 48% had neither. Compared with age-, race-, and sex- (proportionally) matched control subjects from the greater Cincinnati/northern Kentucky region, the attributable risk of hypertension for all causes of first-ever ischemic stroke is 27% (95% CI, 7 to 43); for diabetes, 21% (95% CI, 11 to 29); and for coronary artery disease, 9% (95% CI, 2 to 16). For small-vessel ischemic stroke, the attributable risk of hypertension is 68% (95% CI, 31 to 85; odds ratio [OR], 5.0), and the attributable risk of diabetes is 30% (95% CI, 10 to 45; OR, 4.4). For cardioembolic stroke, the attributable risk of diabetes is 25% (95% CI, 4 to 41; OR, 3.1).

CONCLUSIONS

Stroke of uncertain cause is the most common subtype of ischemic stroke among blacks. Cardioembolic stroke and small-vessel stroke are the most important, identifiable causes of first-ever ischemic stroke among blacks. The incidence rates of cardioembolic and large-vessel stroke are likely underestimated because noninvasive testing of the carotid arteries and echocardiography were not consistently obtained in stroke patients at the 18 regional hospitals. Most small-vessel strokes in blacks can be attributed to hypertension and diabetes.

The Greater Cincinnati/Northern Kentucky Stroke Study: preliminary first-ever and total incidence rates of stroke among blacks

BACKGROUND AND PURPOSE

The Greater Cincinnati/Northern Kentucky Stroke Study was designed to be the first large, population-based metropolitan study of temporal trends in stroke incidence rates and outcome within a biracial population.

METHODS

We are identifying all hospitalized and autopsied cases of stroke and transient ischemic attack (TIA) among the 1.3 million inhabitants of a five-county region of Greater Cincinnati/Northern Kentucky for the period 7/1/93-6/30/94. We have already prospectively monitored for out-of-hospital stroke and TIAs for this same time period at 128 screening sites, including a random sample of all primary care physicians and nursing homes in the region. We have already identified all hospitalized and autopsied cases of stroke and TIA among blacks for 1/1/93-6/30/93 and report preliminary incidence rates for this 6-month period.

RESULTS

The overall incidence rate for all first-ever hospitalized or autopsied stroke (excluding TIAs) among blacks in the Greater Cincinnati region was 288 per 100000 (95% CI, 250 to 325, age- and sex-adjusted to 1990 US population). The overall incidence rate for first-ever and recurrent stroke (excluding TIAs) was 411 per 100000 (95% CI, 366 to 456). By comparison, the overall incidence rate of first-ever stroke among whites in Rochester, Minn, during the period 1985-1989 was 179 per 100000 (95% CI, 164 to 194, age- and-sex adjusted to 1990 US population). The incidence rates among blacks in Greater Cincinnati were substantially greater than the rates among whites in Rochester, Minn, for all age categories except ages 75 and older, for which the rates were similar.

CONCLUSIONS

We conservatively estimate that 731100 first-ever or recurrent strokes occurred in the United States during 1996. Studies of first-ever as well as total stroke among biracial and representative populations are critical for understanding temporal trends in the incidence rate and the burden of stroke in the US population.

Influence of geometrical parameters in different irradiation vessels on UV disinfection rate

Possible differences in the disinfection rate of two irradiation concepts, e.g. irradiation in cuvettes and petri dishes, were examined and quantified on a UV laboratory irradiation plant unit. In addition the geometrical parameters of the irradiation vessels and mixing of the bacterial suspension during UV irradiation were considered. The results showed differences in disinfection rates of more than 2 log between different sample areas in the vessels. The mixing caused an improvement of the disinfection rates in unfavourable irradiation areas of the cuvettes and in contrast a deterioration in all irradiation areas in the petri dishes.

Changes in photosynthetic capacity, carboxylation efficiency, and CO2 compensation point associated with midday stomatal closure and midday depression of net CO2 exchange of leaves of Quercus suber

The carbon-dioxide response of photosynthesis of leaves of Quercus suber, a sclerophyllous species of the European Mediterranean region, was studied as a function of time of day at the end of the summer dry season in the natural habitat. To examine the response experimentally, a "standard" time course for temperature and humidity, which resembled natural conditions, was imposed on the leaves, and the CO2 pressure external to the leaves on subsequent days was varied. The particular temperature and humidity conditions chosen were those which elicited a strong stomatal closure at midday and the simultaneous depression of net CO2 uptake. Midday depression of CO2 uptake is the result of i) a decrease in CO2-saturated photosynthetic capacity after light saturation is reached in the early morning, ii) a decrease in the initial slope of the CO2 response curve (carboxylation efficiency), and iii) a substantial increase in the CO2 compensation point caused by an increase in leaf temperature and a decrease in humidity. As a consequence of the changes in photosynthesis, the internal leaf CO2 pressure remained essentially constant despite stomatal closure. The effects on capacity, slope, and compensation point were reversed by lowering the temperature and increasing the humidity in the afternoon. Constant internal CO2 may aid in minimizing photoinhibition during stomatal closure at midday. The results are discussed in terms of possible temperature, humidity, and hormonal effects on photosynthesis.