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Objective.To determine the relationship between methicillin-resistant Staphylococcus aureus(MRSA) colonization density, colonization site, and probability of infection in a frequently screened cohort of intensive care unit (ICU) patients.Methods.Patients had swab samples tested for MRSA at admission to the ICU, discharge from the ICU, and twice weekly during their ICU stay, and they were followed up for development of MRSA infection. Swab test results were analyzed to determine the proportion of patients colonized and the proportion colonized at each screening site. Hazard of MRSA infection (rate of infection per day at risk) was calculated using a Cox proportional hazards analysis, and risk factors for MRSA infection, including presence of MRSA, degree of colonization, and pattern of colonization were determined.Results.Among the 4,194 patient episodes, 238 (5.7%) had screening results that were positive for MRSA, and there were 34 cases of MRSA infection. The hazard ratio (HR) for developing an infection increased as more sites were colonized (HR, 3.4 for being colonized at more than 1 site compared with colonization at 1 site [95% confidence interval, 1.2-9.9]). Colonization site was predictive of developing infection (HR for nose or throat colonization compared with no colonization, 168 [95% confidence interval, 69-407]).Conclusion.This study demonstrated that the hazard of developing an infection was higher when more sites were colonized and that certain sites were more predictive of infection than others. These results may be useful for predicting infection in ICU patients and may influence treatment.

Monodisperse polymer-mediated platinum (Pt) nanoparticles (NPs) have been synthesized by photoreduction in the presence of poly(ethylenimine) (PEI), a hyperbranched polymer. The formation process of the Pt NPs is pursued by UV−vis spectroscopy, and the formation mechanism is discussed. The morphology and size of the Pt NPs were characterized by transmission electron microscopy (TEM). TEM imaging shows that the Pt NPs’ average diameter is 2.88 ± 0.53 nm. The PEI/Pt NPs were immobilized on glassy carbon electrodes, and the electrocatalytic activity of the catalysts was investigated by cyclic voltammetry. PEI/Pt NPs exhibit very high catalytic activity for a methanol oxidation reaction. PEI/Pt NPs on glassy carbon electrodes are robust, showing good tolerance to poisoning even after many cycles. The electrocatalytic activity of PEI/Pt NPs compares favorably with other polymer-mediated Pt NPs. The results indicate that PEI is an appropriate complexing reducing agent for the photochemical production of Pt NPs and a good capping agent, allowing immobilization of the NPs on the working electrode.

Following complexation with certain dendrimer functionalities, metal ions can be reduced to zerovalent metal nanoparticles via UV irradiation and with the dendrimer oxidized to a radical cation. EPR-silent Zn(II) ions can serve as the oxidizing agent, enabling the nature of the dendrimer radical cation to be examined. Spectral simulations and quantum chemical calculations were carried out to elucidate the nature of the free radicals. Spectral simulations in conjunction with electronic structure calculations suggest that the electron spin density is localized on the central N−C−C−N core structure and delocalized over the N and C atoms in the core. The radical cations of model structures with the ethylenediamine (EDA) core and that of the G0-NH2 polyamidoamine (PAMAM) were found to have a weak central one-electron C−C bond. The description of the molecular structure of the cation falls between the limit of two iminium-type ions with a charge of +0.5 e on each (1/2+R2N= CH21/2•) interacting by a one-electron C−C bond and the other limit of a 1/2+1/2•NR2−CH2−CH2−NR21/2+1/2•structure with a spin of 1/2 and a charge of 1/2 on each N. For EDA, our calculated ionization energies and heats of formation at the coupled cluster (CCSD(T)) level are in good agreement with available experimental data. The ionization energy of the G0-NH2PAMAM was found to be substantially lower than that of EDA. The reduction in the ionization energies for the dendrimers and other effects such as metal−ligand interaction and solvation contribute to the reduction of metal cations by dendrimers with UV irradiation. Similar experiments with the G0-NH2poly(propylene imine) (PPI) did not produce metal nanoparticles, indicating these effects are not as favorable as those for G0-NH2PAMAM.

Objective. To implement and evaluate the effect of a computerized decision support tool on antibiotic use in an intensive care unit (ICU).Design. Prospective before-and-after cohort study.Setting. Twenty-four bed tertiary hospital adult medical/surgical ICU.Participants. All consecutive patients from May 2001 to November 2001 (N = 524) and March 2002 to September 2002 (N = 536).Intervention. A real-time microbiology browser and computerized decision support system for isolate directed antibiotic prescription.Main outcome measures. Number of courses of antibiotic prescribed, antibiotic utilization (defined daily doses (DDDs)/100 ICU bed-days), antibiotic susceptibility mismatches, and system uptake.Results. There was a significant reduction in the proportion of patients prescribed carbapenems [odds ratio (OR) = 0.61, 95% confidence interval (CI) = 0.39–0.97, P = 0.04], third-generation cephalosporins (OR = 0.58, 95% CI = 0.42–0.79, P = 0.001), and vancomycin (OR = 0.67, 95% CI = 0.45–1.00, P = 0.05) after adjustment for risk factors including Apache II score, suspected infection, positive microbiology, intubation, and length of stay. The decision support tool was associated with a 10.5% reduction in both total antibiotic utilization (166–149 DDDs/100 ICU bed days) and the highest volume broad-spectrum antibiotics. There were fewer susceptibility mismatches for initial antibiotic therapy (OR = 0.63, 95% CI = 0.39–0.98, P = 0.02) and increased de-escalation to narrower spectrum antibiotics. Uptake of the program was high with 6028 access episodes during the 6-month evaluation period.Conclusions. This tool streamlined collation and clinical use of microbiology results and integrated into the daily ICU workflow. Its introduction was accompanied by a reduction in both total and broad-spectrum antibiotic use and an increase in the number of switches to narrower spectrum antibiotics.

The proportion of human immunodeficiency virus type 1 (HIV-1) among Vietnamese injecting drug users (IDUs) in Melbourne, Australia exceeds that of the background population. To investigate the molecular epidemiology of HIV-1 among this group, the C2-V4 region of the HIV-1 envelope was directly sequenced from 11 Vietnamese Australians and 19 non-Vietnamese Australian controls. A significant difference in the distribution of the HIV-1 subtypes was demonstrated, with greater than 50% of Vietnamese Australian IDU shown to be infected with CRF01_AE—the predominant subtype in Southeast Asia, rather than subtype B, which dominates the Australian epidemic and which was found in 89.5% of the non-Vietnamese controls. The genetic diversity of the CRF01_AE epidemic in Vietnamese Australian IDUs was substantially lower that that of the background subtype B, consistent with a more recent introduction of a limited number of viral strains from Vietnam. These results support public health policy targeting Australian IDUs of Vietnamese ethnicity as a distinct vulnerable population.

Microcontact printing (μCP) is a soft lithographic technique used to transfer patterned thin organic films to surfaces with submicrometer resolution. Here, various concentrations of fourth-generation NH2-terminated polyamidoamine dendrimers are used as the “ink” in μCP. A patterned monolayer is formed from dilute solution (1 μmol); however, this structure is not stable under ambient conditions. Increasing the dendrimer concentration (up to 1 mmol) results in stable multilayer structures up to roughly 60 nm in height, as characterized by atomic force microscopy. The relationship between dendrimer concentration and layer thickness is explored.

We have prepared Langmuir−Blodgett monolayers of hexadecylquinolinium tricyanoquinodimethanide (C16H33Q⁺-3CNQ^-) on gold surfaces and characterized the structure by surface plasmon resonance (SPR), X-ray photoelectron spectroscopy (XPS), reflection−absorption infrared spectroscopy (RAIRS), Raman spectroscopy, and water contact angle measurements. We compare the IR and UV−vis spectra of C16H33Q⁺-3CNQ^- to a series of compounds that contain the key functional groups in the titled compound to help assign the spectral features. The surface spectroscopic measurements indicate that the molecules in the monolayer are aligned such that the two terminal cyano groups are adsorbed on the Au surface, and that the aliphatic chain is away from that surface. The thickness of the monolayer was measured by XPS to be ~ 26 Å and suggests that the molecules are tilted ~40° away from the surface normal. High-resolution XPS and spectroelectrochemical measurements of C16H33Q⁺-3CNQ^- strongly suggest that it is a ground-state zwitterion in both the adsorbed and solvated forms.

Focuses on the Clarion River as a habitat for brown trouts in Pennsylvania. Size of the river; Impact of the paper mill on the viability of the river; Branches of the river.

Evidence is presented here for very significant improvements in film quality when Au is deposited on a self-assembled monolayer of amine-terminated poly(amidoamine) (PAMAM) dendrimers (generation G8) on SiOx. In addition, the nanomechanical response of the monolayer dendrimer film itself and the Au/dendrimer bilayer configuration is reported for the first time. Ultrathin (12.5 nm) Au grown on the native oxide of Si(100) results in an apparently continuous but poorly adherent film with vertical RMS roughness, ≈1 nm, and occasional, very much larger scale (≈75 nm) features. Dendrimer-mediated Au films have substantially reduced roughness (≈0.4 nm) and no large-scale features. Nanoindentation studies demonstrate surprisingly large differences in the mechanical responses of Au films with and without a dendrimer interlayer. The nanoindentation hardness (a measure of resistance to plastic deformation) of the dendrimer-mediated 12.5-nm Au film is significantly higher than that of the 12.5-nm Au layer alone. This mechanical strengthening is attributed to the compressed and confined nature of the dendrimer interlayer and points to the possibility of using hybrid organic/inorganic nanocomposites as tribomaterials.

Highly ordered alkanethiol self-assembled monolayers (SAMs) on gold substrates are suitable models of boundary layer lubricants and may be used in actual nanoscale device applications. Here, such monolayers were studied by spectroscopic methods as a function of tribological wear (rubbing) using a pin-on-disk microtribometer. The coefficient of friction (COF) (ratio of the frictional force to the load) was measured with the tribometer, and reflectance infrared spectra and X-ray photoelectron spectra were obtained as the monolayer film failed and the COF changed. The results show that it is possible to correlate disorder in the monolayer film with tribological failure of the film, and that continued rubbing produces a chemical change in the monolayer film. Disorder in the monolayer is distinct from the influence of wear in the underlying gold substrate. Aged SAMs, having sulfonate rather than thiol headgroups and initially less well ordered, behave differently to the well-ordered freshly prepared SAMs. Interestingly, they show a lower COF over many more cycles of exposure to the rubbing pin. The impact of the mechanism of film failure in boundary layer lubrication is discussed.

Stress fractures in women athletes may be the presentation of more serious underlying medical conditions, such as the female athlete triad. This article presents a general overview of stress injury to the bone among women athletes. The history of women in sports, basic bone biology, the female athlete triad, and risk factors for stress fractures are discussed. Stress fractures can occur at any anatomic site in women; however, they tend to occur more frequently in the pelvis, sacrum, and femoral neck. Stress fractures at these sites, therefore, are discussed in detail. Surgical indications are also reviewed.

Experimental investigations of β-hydrogen elimination from alkoxy and alkyl groups bound to a Cu(111) surface have been coupled with computational studies of gas-phase analogues to provide insight into the transition state for catalytic hydrogenation and dehydrogenation on metal surfaces. Previous studies have shown that fluorination increases the activation barrier (ΔEact) to β-hydrogen elimination in ethoxy groups (RCH2O(ad) → RCH&dbd;O(ad) + H(ad), where R = CH3, CFH2, CHF2, CF3) and propyl groups (RCH2CH2,(ad) → RCH&dbd;CH2,(ad) + H(ad), where R = CH3, CF3) on the Cu(111) surface. The increase in barrier height with increasing fluorination was attributed to the inductive influence of fluorine, which energetically destabilizes a hydride-like transition state of the form [RC^δ+···H^δ-]^‡. In this paper, deuterium kinetic isotope effects (DKIE) show that fluorination does not alter the mechanism for β-hydrogen elimination from ethoxy groups. Furthermore, the DKIE measurements confirm that the effects of fluorine on the kinetics of β-hydrogen elimination do not result from the change in mass when hydrogen is substituted by fluorine. A systematic study of fluorine substitution of surface-bound isopropoxy groups reveals combined steric and electronic effects. An excellent correlation is found between the ΔEact for β-hydrogen elimination in adsorbed alkoxy groups and the calculated reaction energetics (ΔHrxn) for gas-phase dehydrogenation of fluorinated alcohols in trans antiperiplanar conformations (e.g., RCH2OH(g) → RCH&dbd;O(g) + H2,(g), where the hydroxyl hydrogen is antiperiplanar to a carbon and the oxygen is antiperiplanar to a fluorine). Hammett plots for β-hydrogen elimination give a reaction parameter of ρ = −26. These correlations both suggest that the transition state for β-hydrogen elimination develops a greater partial positive charge on the carbinol carbon than is found in the adsorbed reactant. Furthermore, the transition state is energetically late in the reaction coordinate for β-hydrogen elimination.

Cobalt–carbon thin films proposed for use as granular magnetic media are generally prepared by co-deposition sputtering. An alternative method is nanolamination of the component layers (media and matrix) followed by annealing. We have produced and characterized thin-film granular structures prepared from nanolaminate layers of Co and CNx. For the as-deposited samples, only metallic cobalt is observed with XPS and a constant nitrogen concentration of x ~ 0.15 was measured for the carbon nitride layers. The annealed films have oxidized cobalt in the very near surface region. Atomic force microscopy measurements show that the surface of the film roughens significantly upon annealing, with the RMS roughness increasing from 0.2 to 1.0 nm. Thus, it appears that the nanostructural evolution caused by the annealing process, which gives rise to grain formation, also degrades the smooth surface of the CNx capping layer and exposes some of the cobalt to ambient. The potential implications of these observations on tribological performance are explored. Copyright © 2000 John Wiley & Sons, Ltd.

Cobalt–carbon thin films proposed for use as granular magnetic media are generally prepared by co‐deposition sputtering. An alternative method is nanolamination of the component layers (media and matrix) followed by annealing. We have produced and characterized thin‐film granular structures prepared from nanolaminate layers of Co and CNx. For the as‐deposited samples, only metallic cobalt is observed with XPS and a constant nitrogen concentration of x∼ 0.15 was measured for the carbon nitride layers. The annealed films have oxidized cobalt in the very near surface region. Atomic force microscopy measurements show that the surface of the film roughens significantly upon annealing, with the RMS roughness increasing from 0.2 to 1.0 nm. Thus, it appears that the nanostructural evolution caused by the annealing process, which gives rise to grain formation, also degrades the smooth surface of the CNxcapping layer and exposes some of the cobalt to ambient. The potential implications of these observations on tribological performance are explored. Copyright © 2000 John Wiley & Sons, Ltd.

Hexadecylquinolinium tricyanoquinodimethanide (1), a unimolecular rectifier of electrical current with a large ground-state dipole moment (43 ± 8 D), reveals large hypsochromic shifts of the absorption spectrum. Two fluorescent emissions were observed:  one in the visible region (quantum yield φ ≈ 0.01, not solvatochromic) and one in the near-infrared spectrum (weakly solvatochromic). Using a prolate spheroidal cavity model and the absorption maxima measured in eight solvents, the excited-state dipole moment of 1 is estimated as 8.7 D. The NMR spectral lines broaden above 330 K and lose the multiplet structure. The core-level N 1s XPS spectrum reveals the three expected N valence states. The valence-level XPS spectrum can be correlated with theory. Simultaneous cyclic voltammetry and electron spin resonance of the radical anion of 1 shows that the spin density in the LUMO of 1 is concentrated on the tricyanoquinodimethanide portion of the anion. The molecule is clearly zwitterionic in the ground state, both in LB films and in solution, and is undissociated (“neutral”) in its first excited state.

The range of diecasting machines has increased, in size and locking force, making possible the production of engine cylinder blocks, transmission housings, and other large and complex components, especially in aluminium alloys. Instrumentation has been developed to measure and control the speed and pressure of metal injection, temperature control of the dies, measurement of machine locking force, and oscillographic monitoring of the diecasting process, sometimes with a computer built into the equipment. Large diecasting plants can now receive molten aluminium alloy consignments direct from the secondary metal smelter. In molten-metal handling in the diecasting plant, further developments are being made in furnace design, both for bulk metal melting of scrap, runners, and ingots and in the bale-out furnaces adjacent to the diecasting machines. Several producers of zinc alloy diecastings are now making their own alloy, under carefully controlled conditions. During the past ten years most diecasting companies have been successful in mechanizing at least part of their production. Most zinc alloy diecastings are now produced automatically and considerable development in the much more difficult automation of aluminium diecasting has been. achieved. Methods of automatic ladling, lubrication, and trimming and machining processes linked with automatic diecasting production are discussed. New deburring processes and specialpurpose machines and robots used in handling all stages of the manufacturing processes are described. The positioning and the correct dimensioning of runners and gates has received much attention during the past ten years. Die designers are obtaining valuable help from the mathematical formulae and monographs which have been developed. While the major production of zinc, aluminium, and magnesium alloy diecastings involves standard alloys that were well known ten years ago, some new alloys have been developed. The hypereutectic aluminium–silicon alloys used in the production of some cylinder blocks are described. The development of new die materials, including those based on molybdenum, has helped to make possible the diecasting of high melting point alloys, including stainless steel. Some new diecasting techniques are discussed, including the possibilities of the oxygen-purging or pore-free diecasting process, developed in Japan, but so far little explored in the West. Improved finishing processes for the electroplating of zinc alloy diecastings are described.

Liver mitochondria from α-tocopherol deficient rats swell more rapidly, both spontaneously and in the presence of GSH, than those from control animals. The increased swelling of deficient mitochondria induced by GSH was completely eliminated when mitochondria were left longer than two hours at 0° in the suspending medium. GSH-induced swelling of liver mitochondria from α-tocopherol deficient rats is reversed by ATP, polyvinyl pyrrolidone (PVP), and by oral administration of α-tocopherol (2 mg/day per rat). Swelling of mitochondria in the above system was completely inhibited by the respiratory chain inhibitor, cyanide (0.001 M), and partially by azide (0.001 M). We suggest that the swelling tendency of liver mitochondria from α-tocopherol deficient rats might be associated with an altered respiratory mechanism and/or an alteration in membrane permeability.

Fourier-transform infrared reflection absorption spectra (FT-IRAS) have been obtained for 1-propoxide and a set of deuterated 1-propoxides at saturation coverages on the Cu(111) surface. These stable species are formed by the reaction of 1-propanol with the preoxidized Cu(111) surface. At elevated temperatures the propoxides undergo β-hydride elimination and desorb as propanals. Temperature programmed reaction (TPR) spectra for the decomposition process reveal both a primary isotope effect and secondary isotope effects. The FT-IRAS spectra have been compared to the reflection infrared spectra of self-assembled monolayers containing long alkyl chains. The spectra show evidence for both crystalline-like packing and conformational disorder in the adlayer. This suggests the presence of both ordered and disordered domains of the alkoxides on the Cu(111) surface.

The silylcobalt complexes [R2R′SiCo(CO)4] (R, R′ = Ph, Me) reacted with dinitrogen complexes of the type [M(N2)2(P)4] (M = Mo, W; P = tertiary phosphine) to give new silyldiazenido complexes trans-[M(NNSiR2R′)(P)4][(μ-OC)Co(CO)3], which were further converted to silylhydrazido(2−) complexes such as trans-[WX(NNHSiR2R′)(dpe)2][Co(CO)4] by treatment with HX (dpe = Ph2PCH2CH2PPh2; X = OH, OMe, Br).

AbstractA cross-sectional serological survey was undertaken in 82 randomly selected high-risk healthcare workers previously vaccinated with the hepatitis B vaccine. The study design allowed for the identification and testing for hepatitis B surface antibody in equal numbers of employees in six-month intervals up to five years after vaccination. The results showed a consistent decline in antibody level with time, and an increasing proportion of participants with antibody levels below the commonly accepted protective level of =10 S/N (sample counts/negative control counts) radioimmunoassay units. The percent of vaccinees whose S/N ratio was greater than 10 fell from 10% at one year, to 25% at two years, to over 50% at four years. Based on these figures, as well as the financial costs of hepatitis B in employees and the predictability of booster immunization, it was possible to assess the cost benefit of a hospital policy for reimmunization. At our institution, a strategy of revaccination at fixed intervals could save up to $200,000 over a ten-year period if revaccination was not offered and vaccine efficacy declined. The information obtained should help determine the need for revaccination and the advantages and disadvantages of alternative revaccination strategies.

By using small fluorinated ethers as models for perfluoropolyalkyl ether lubricants, we have been able to determine the effect of fluorine on the bonding and orientation of the alkylethers adsorbed on the Cu(111) surface. The desorption energies have been determined by using temperature-programmed desorption and the orientations by Fourier transform infrared absorption reflection spectroscopy (FT-IRAS). The model compounds studied were dioxolane (CH2OCH2OCH2) and perfluorodioxolane (CF2OCF2OCF2), diethyl ether ((CH3CH2)2O) and perfluorodiethyl ether ((CF3CF2)2O), dimethoxymethane ((CH3O)2CH2) and perfluorodimethoxymethane ((CF3O)2CF2), dimethyl ether ((CH3)2O) and perfluorodimethyl ether ((CF3)2O). All of the molecules studied adsorb molecularly and reversibly on the Cu(111) surface exhibiting first-order desorption kinetics. Upon fluorination of the alkyl ethers, the adsorbate−metal bond was weakened by 5−7 kcal/mol. The hydrogenated ethers exhibit repulsive adsorbate−adsorbate interactions, while the fluorinated ethers have attractive adsorbate−adsorbate interactions. At saturation coverages, the FT-IRAS spectra show that the diethyl ethers are oriented with their molecular axes parallel to the Cu(111) surface. 1,3-Dioxolane was oriented with its ring plane parallel to the metal surface.

1. Heteronuclear 1H/15N n.m.r. experiments are described in which 15N labelling of cellular metabolites is detected via their proton resonances. 2. These n.m.r. experiments have been used to monitor label redistribution amongst extracellular metabolites in cultures of mammalian cells incubated with L-[2-15N]glutamine, L-[5-15N]glutamine and 15NH4Cl. Label redistribution was monitored in two HeLa cell lines and in two CHO cell lines which showed a range of extractable activities of glutamate dehydrogenase, glutaminase and glutamine synthetase. 3. In cells incubated with L-[2-15N]glutamine the 15N label was subsequently found in a number of metabolites including alanine, aspartate, glycine and pyrrolidone-5-carboxylic acid. There was no detectable production of 15NH4+, showing that most of the glutamate formed in the reaction catalysed by glutaminase was subsequently transaminated rather than oxidatively deaminated by glutamate dehydrogenase. 4. Incubation of cells with L-[5-15N]glutamine showed that the ammonia in the cultures was derived predominantly from the amide group of glutamine. 5. The rate of formation of L-[5-15N]glutamine in cells incubated with 15NH4Cl was used to estimate glutamine synthetase flux in vivo. Flux in this reaction was only observable in the two CHO cell lines which express relatively high levels of the enzyme.

The results of an initial study on the feasibility of using the phosphonium analog of choline to follow the metabolism of phosphatidylcholine in tumors in vivousing 31P NMR are reported. C3H/He mice bearing a mammary carcinoma tumor on the foot pad were fed a choline‐free diet supplemented with the phosphonium analog of choline. Metabolites of this compound, including the phosphonium analogs of phosphatidylcholine, phosphocholine, glycerophosphocholine, and betaine were observed noninvasively in vivoin tumors by 31P NMR after 2–3 weeks of feeding. Clearance of these phosphonium‐labeled metabolites from tumors was measured after a change to a choline‐containing diet. Significant decreases were seen in the levels of the analogs of betaine (P< 0.003) and phosphatidylcholine (P< 0.004) by Day 4. A significant increase in the level of authentic phosphocholine (P< 0.003) occurred over the same time period.

Fourier transform infrared reflection absorption spectra (FT-IRAS) have been obtained for adsorbed monolayers of propene and a set of fluorinated propenes (CFH2CH&dbd;CH2, CF3CH&dbd;CH2, and CF3CF&dbd;CF2) on the Cu(111) surface. These species interact weakly with the copper surface. The FT-IRAS spectra indicate that the molecules lie flat with the plane of the molecule defined by the C&sbd;C&dbd;C atoms essentially parallel to the surface regardless of the degree of fluorination. Quantitative analysis of the orientation of hexafluoropropene determines the tilt of the molecular plane with respect to the surface to be 11°. The results for propene indicate a molecular tilt of 20°. Where the ν(C&dbd;C) mode can be identified in the spectra of the adsorbed molecules, there is no perturbation of its frequency, which indicates that there is little backdonation between the metal and the π* orbital of the propene.

Mycobacterium ulcerans, the organism which causes Buruli or Bairnsdale ulcer, has never been isolated in culture from an environmental sample. Most foci of infection are in tropical regions. The authors describe the first 29 cases of M. ulcerans infection from a new focus on an island in temperate southern Australia, 1992–5. Cases were mostly elderly, had predominantly distal limb lesions and were clustered in a small region in the eastern half of the main town on the island. The authors suspected that an irrigation system which lay in the midst of the cluster was a source of infection. Limitation of irrigation was associated with a dramatic reduction in the number of new cases. These findings support the hypothesis that M. ulcerans has an aquatic reservoir and that persons may be infected directly or indirectly by mycobacteria disseminated locally by spray irrigation.