Cost-effectiveness of selective decontamination of the digestive tract to decrease infectious complications in colorectal cancer surgery: An analysis of the SELECT trial.

INTRODUCTION: Selective decontamination of the digestive tract (SDD) is effective in reducing infectious complications in elective colorectal cancer (CRC) surgery. However, it is unclear whether SDD is cost-effective compared to standard antibiotic prophylaxis. MATERIAL & METHODS: Economic evaluation alongside multicenter randomized controlled trial, the SELECT-trial, from a healthcare perspective. Patients included underwent elective surgery for non-metastatic CRC. The intervention group received oral non-absorbable colistin, tobramycin and amphotericin B (SDD) next to standard antibiotic prophylaxis. Both groups received a single shot intravenous cefazolin and metronidazole preoperatively as standard prophylaxis. Occurrence of postoperative infectious complication in the first 30 postoperative days was extracted from medical records, Quality-Adjusted Life-Years (QALYs) based on the ED-5D-3L, and healthcare costs collected from the hospital's financial administration. RESULTS: Of the 455 patients, 228 were randomly assigned to intervention group and 227 patients to the control group. SDD significantly reduced the number of infectious complications compared to control (difference = -0.13, 95 % CI -0.05 to -0.20). No difference was found for QALYs (difference = 0.002, 95 % CI -0.002 to 0.005). Healthcare costs were statistically significantly lower in the intervention group (difference = -€1258, 95 % CI -2751 to -166). The ICER was -9872 €/infectious complication prevented and -820,380 €/QALY gained. For all willingness-to-pay thresholds, the probability that prophylactic SDD was cost-effective compared to standard prophylactic practice alone was 1.0. CONCLUSION: The addition of SDD to the standard preoperative intravenous antibiotic prophylaxis is cost-effective compared to standard prophylactic practice from a healthcare perspective and should be considered as the standard of care.

Selective Decontamination with Oral Antibiotics in Colorectal Surgery: 90-day Reintervention Rates and Long-term Oncological Follow-up.

BACKGROUND: Oral antibiotics (OAB) in colorectal surgery have been shown to reduce surgical site infections (SSIs) and possibly anastomotic leakage. However, evidence on long-term follow-up, reintervention rates and 5-year oncological follow-up is lacking. The current study aims at elucidating this knowledge gap. METHODS: This study evaluated the long-term effectiveness of perioperative 'Selective decontamination of the digestive tract' (SDD) in colorectal cancer surgery. The primary outcome was anastomotic leakage within 90 days, secondary outcomes included infectious complications, reinterventions, readmission, hospital stay, and 5-year overall and disease-free-survival. Statistical analysis including univariate and multivariate analysis was performed to identify predictors of 90-day outcomes, and Kaplan-Meier survival analysis was used for the 5-year survival outcomes. RESULTS: In total 455 patients were analyzed, 228 participants in the SDD group and 227 in the control group. Anastomotic leakage rate was not statistically different between the SDD and control group (6.6% versus 9.7%). One or more infectious complications occurred in 15.4% of patients in the SDD group and in 28.2% in the control group (OR 0.46, 95% C.I. 0.29 - 0.73). In the SDD group 8,8% of patients required a reintervention compared to 16,3% of patients in the control group (OR 0.47, 95% C.I. 0.26 - 0.84). After multivariable analysis SDD remained significant in reducing both infectious complications and reinterventions after 90-days follow-up. There was no difference between SDD and control group in 5-year overall survival and disease-free-survival. CONCLUSION: SDD as OAB is effective in reducing 90-days postoperative infectious complications and reinterventions. As such, SDD as standard OAB in elective colorectal surgery is highly recommended.

Environmental life cycle assessment of production of the high intensity sweetener steviol glycosides from Stevia rebaudiana leaf grown in Europe: The SWEET project.

Purpose: There is an increasing interest in the use of non-nutritive sweeteners to replace added sugar in food and beverage products for reasons of improving consumer health. Much work has been done to understand safety of sweeteners, but very little on sustainability. To address that gap, this study presents the results of a life cycle assessment (LCA) of production of rebaudioside A 60%, 95% pure (RA60) steviol glycoside mix from Stevia rebaudiana leaf grown in Europe. Methods: An attributional cradle-to-factory-gate life cycle assessment was conducted on growing of stevia leaves and extraction of steviol glycosides in Europe. Primary data were used from a case study supply chain. Results are reported in impact categories from the ReCiPe 2016 (H) method, with focus given to global warming potential, freshwater eutrophication, water consumption, and land use. Impacts are expressed both in terms of production mass and sweetness equivalence, a common metric for understanding high intensity sweetener potency. Sweetness equivalence of RA60 is typically 200 to 300 times that of sugar. Comparison of environmental impact is made to sugar (sucrose) produced from both cane and beets. The research is part of the EU project SWEET (sweeteners and sweetness enhancers: impact on health, obesity, safety, and sustainability). Results and discussion: Global warming potential for production of RA60 was found to be 20.25 kgCO2-eq/kgRA60 on a mass basis and 0.081 kgCO2-eq/kgSE on a sweetness equivalence basis. Field production of stevia leaves was found to be the main source of impact for most impact categories, and for all four focus categories. Extraction of the RA60 was the main source of impact for the others. Leaf processing and seedling propagation were minor contributors to life cycle impact. Removal of international transport from the supply chain reduced global warming potential by 18.8%. Compared with sugar on a sweetness equivalence basis, RA60 has approximately 5.7% to 10.2% the impact for global warming potential, 5.6% to 7.2% the impact for land use, and is lower across most other impact categories. Conclusion: This is the first LCA of steviol glycoside mix RA60 produced from leaf in Europe. The results indicate that RA60 can be used to reduce environmental impact of providing a sweet taste by replacing sugar across all impact categories. However, it is important to note that specific formulations in which RA60 is used will have a bearing on the final environmental impact of any food or beverage products. For solid foods, this requires further research. Supplementary Information: The online version contains supplementary material available at 10.1007/s11367-022-02127-9.

Robust impurity detection and tracking for tokamaks.

A robust impurity detection and tracking code, able to generate large sets of dust tracks from tokamak camera footage, is presented. This machine learning-based code is tested with cameras from the Joint European Torus, Doublet-III-D, and Magnum-PSI and is able to generate dust tracks with a 65-100% classification accuracy. Moreover, the number dust particles detected from a single camera shot can be up to the order of 1000. Several areas of improvement for the code are highlighted, such as generating more significant training data sets and accounting for selection biases. Although the code is tested with dust in single two-dimensional camera views, it could easily be applied to multiple-camera stereoscopic reconstruction or nondust impurities.

Ionic Liquid-Stabilized Titania Quantum Dots Applied in Adhesive Resin.

Quantum dots (QDs; 1 to 10 nm) were recently synthesized by sol-gel and used as nonagglomerated nanoparticles in adhesive resin. The sol-gel process presented a low yield and resulted in a liquid product without stability. In this study, an imidazolium ionic liquid (IL; 1- n-butyl-3-methylimidazolium tetrafluoroborate, BMI.BF4) was used as stabilizing agent to synthesize titanium dioxide QDs (TiO2QDs/BMI.BF4) via a chemical route. The product was isolated as powder after washing, centrifuging, and drying. An experimental adhesive resin was formulated by mixing methacrylate monomers and a photoinitiator system. The TiO2QDs/BMI.BF4 powder was incorporated at 2.5 (G2.5%) and 5 (G5%) wt% in the adhesive resin, and one group remained without TiO2QDs/BMI.BF4 powder as the control (Gctrl). The TiO2QDs/BMI.BF4 powder was analyzed by micro-Raman spectroscopy, thermogravimetry, and transmission electron microscopy. The dispersion of TiO2QDs/BMI.BF4 powder was analyzed in the polymerized adhesive resin with transmission electron microscopy and fluorescence microscopy. The adhesive resins were evaluated for immediate and long-term antibacterial activity, cytotoxicity, polymerization behavior, degree of conversion, softening in solvent, immediate and long-term microtensile bond strength, and fracture pattern. The TiO2QDs/BMI.BF4 powder showed peaks of anatase and rutile and 26 wt% of BMI.BF4. TiO2QDs/BMI.BF4 presented a minimum size of 1.19 nm, a maximum size of 7.11 nm, and a mean ± SD size of 3.54 ± 1.08 nm. TiO2QDs/BMI.BF4 was dispersed in the adhesive resin without agglomeration, presenting intermittent luminescence by blinking. The addition of any tested concentration of TiO2QDs/BMI.BF4 powder provided immediate and long-term antibacterial activity without cytotoxic effect against the pulp fibroblasts. Furthermore, compared with Gctrl, G2.5% showed reliable polymerization behavior and degree of conversion without differences for softening in solvent with maintenance of bond adhesion to tooth immediately and over time. Thus, the incorporation of 2.5 wt% of TiO2QDs/BMI.BF4 in adhesive resin showed reliable physical, chemical, and biological properties.

Advanced Thomson scattering system for high-flux linear plasma generator.

An advanced Thomson scattering system has been built for a linear plasma generator for plasma surface interaction studies. The Thomson scattering system is based on a Nd:YAG laser operating at the second harmonic and a detection branch featuring a high etendue (f/3) transmission grating spectrometer equipped with an intensified charged coupled device camera. The system is able to measure electron density (n(e)) and temperature (T(e)) profiles close to the output of the plasma source and, at a distance of 1.25 m, just in front of a target. The detection system enables to measure 50 spatial channels of about 2 mm each, along a laser chord of 95 mm. By summing a total of 30 laser pulses (0.6 J, 10 Hz), an observational error of 3% in n(e) and 6% in T(e) (at n(e) = 9.4 × 10(18) m(-3)) can be obtained. Single pulse Thomson scattering measurements can be performed with the same accuracy for n(e) > 2.8 × 10(20) m(-3). The minimum measurable density and temperature are n(e) < 1 × 10(17) m(-3) and T(e) < 0.07 eV, respectively. In addition, using the Rayleigh peak, superimposed on the Thomson scattered spectrum, the neutral density (n(0)) of the plasma can be measured with an accuracy of 25% (at n(0) = 1 × 10(20) m(-3)). In this report, the performance of the Thomson scattering system will be shown along with unprecedented accurate Thomson-Rayleigh scattering measurements on a low-temperature argon plasma expansion into a low-pressure background.

Underwater in situ measurements of radionuclides in selected submarine groundwater springs, Mediterranean Sea.

The application of the in situ measurement system 'KATERINA' for monitoring of radon progenies in submarine groundwater discharge (SGD) was investigated at different locations in the Mediterranean Sea (Chalkida, Stoupa, Korfos and Cabbé). At Chalkida and Stoupa radon progenies concentration exhibited almost constant values of 1.2 ± 0.1 and 2.5 ± 0.2 Bq l(-1), respectively. At Korfos these activities ranged between 1.4 ± 0.1 and 2.3 ± 0.2 Bq l(-1) exhibiting inverse relationship with salinity. At Cabbé the in situ measured data were compared with radon measurements obtained by liquid scintillation counter. The system also resolved radon progeny variations of SGD on time scales above 1 h. The radioactivity levels of radon progenies from all sites were found considerably lower (approximately 2 orders of magnitude) than the commonly accepted limits for radon in drinking water.

Occurrence of mycotoxins in feedstuffs of dairy cows and estimation of total dietary intakes.

A survey was conducted to determine the occurrence of mycotoxins in feedstuffs of dairy cows in the Netherlands and to estimate total dietary intakes of these compounds. Twenty-four dairy farms were visited twice and samples taken of all diet ingredients. Feed intake data were collected by means of questionnaires. A total of 169 feed samples were collected and analyzed for 20 mycotoxins using a liquid chromatography tandem mass spectrometry multimethod. Silage and compound feed were the main diet ingredients, representing on average 67 and 23% of dry matter intake, respectively. Deoxynivalenol (DON), zearalenone, roquefortine C, and mycophenolic acid were the mycotoxins with the highest incidence. The incidence of DON in silage, compound feed, and feed commodity samples was 38 to 54%. The incidence of zearalenone in silage, compound feed, and feed commodity samples was 17 to 38%. The DON and zearalenone had a low incidence in forage samples and were not detected in ensiled by-product samples. Roquefortine C and mycophenolic acid were only detected in silage and ensiled by-product samples (incidence 7 to 19%). Fumonisins B(1) and B(2) were detected in 2 compound feed samples and one feed commodity sample. Aflatoxins B(1), B(2), G(1), and G(2), ochratoxin A, T-2 and HT-2 toxin, 3-acetyl-DON, 15-acetyl-DON, diacetoxyscirpenol, sterigmatocystin, fusarenon-X, ergotamine, and penicillinic acid were not detected in any of the samples. Average concentrations of DON, zearalenone, roquefortine C, and mycophenolic acid in complete diets were 273, 28, 114, and 54 microg/kg, respectively. Maximum concentrations were 969, 203, 2,211, and 1,840 microg/kg, respectively. Calculated average daily intakes of these mycotoxins were 5.0, 0.5, 2.0, and 0.9 mg/animal, respectively, and maximum daily intakes 19.3, 3.5, 38.9, and 32.3 mg/animal, respectively. Corn silage was the major source of all 4 of these mycotoxins in the diet. Extremely high concentrations of roquefortine C and mycophenolic acid (up to 45 and 25 mg/kg, respectively) were detected in visibly molded areas in surface layers of corn silage. These areas appeared to be the main source of roquefortine C and mycophenolic acid in the diet. Because carry-over of DON, zearale-none, roquefortine C, and mycophenolic acid into milk is negligible, their occurrence in feedstuffs is not considered of significant concern with respect to the safety of dairy products for consumers. Potential implications for animal health are discussed.

Under-reporting of HIV infection among cohorts of TB patients in the WHO European Region, 2003-2004.

SETTING: The World Health Organization (WHO) European Region, which includes 52 countries. OBJECTIVE: To assess an epidemiological data collection tool implemented in 2004 for recording human immunodeficiency virus (HIV) status among tuberculosis (TB) patients. DESIGN: Based on WHO estimates, the reported number of TB patients with HIV was compared with the number expected. The analysis included all forms of TB and was restricted to adults, wherever possible. The numbers of TB patients detected from HIV/acquired immune-deficiency syndrome (AIDS) programmes (NAPs) were also assessed. RESULTS: In 2003, 20 (38%) National TB Programmes (NTPs) reported 4602 (35%) HIV-infected TB cases of 13117 expected; in 2004, 23 (44%) NTPs reported 5902 (42%) cases of 13901 expected. In 2003, 47 (90%) NAPs reported 3575 (27%) TB cases as a new AIDS diagnosis, while in 2004, 40 (77%) NAPs reported 3901 (28%) TB cases. Those countries that did report, reported on average 60-65% of expected cases, irrespective of the kind of programme and the year. CONCLUSION: Most NTPs did not report TB cases with HIV infection. Overall, the number of cases reported in countries that reported data from either NTPs or NAPs was significantly lower than expected. Improved surveillance requires concerted efforts from both NTPs and NAPs.

Occurrence of mycotoxins in maize, grass and wheat silage for dairy cattle in the Netherlands.

The occurrence of mycotoxins in 140 maize silages, 120 grass silages and 30 wheat silages produced in the Netherlands between 2002 and 2004 was determined using a liquid chromatography coupled with tandem mass spectrometry detection (LC-MS/MS) multi-method. Deoxynivalenol (DON) was detected above the limit of quantification (LOQ) of 250 µg kg⁻¹ in 72% of maize and 10% of wheat silages. Average DON concentrations were 854 and 621 µg kg⁻¹, respectively, and maximum concentrations 3142 and 1165 µg kg⁻¹, respectively. Zearalenone was detected above the LOQ of 25 µg kg⁻¹ in 49% of maize and 6% of grass silages. Average zearalenone concentrations were 174 and 93 µg kg⁻¹, respectively, and maximum concentrations 943 and 308 µg kg⁻¹, respectively. The incidences and average concentrations of DON and zearalenone in maize silage were highest in 2004. The incidence of other mycotoxins was low: fumonisin B1 and 15-acetyl-DON were detected in 1.4 and 5% of maize silages, respectively, and roquefortin C in 0.8% of grass silages. None of the silages contained aflatoxins, ochratoxin A, T2-toxin, HT2-toxin, sterigmatocystin, diacetoxyscirpenol, fusarenon-X, ergotamine, penicillinic acid, or mycophenolic acid. This study demonstrates that maize silage is an important source of DON and zearalenone in the diet of dairy cattle. Since the carryover of these mycotoxins into milk is negligible, their occurrence in feed is not considered to be of significant concern with respect to the safety of dairy products for consumers. Potential implications for animal health are discussed.

Quantifying submarine groundwater discharge in the coastal zone via multiple methods.

Submarine groundwater discharge (SGD) is now recognized as an important pathway between land and sea. As such, this flow may contribute to the biogeochemical and other marine budgets of near-shore waters. These discharges typically display significant spatial and temporal variability making assessments difficult. Groundwater seepage is patchy, diffuse, temporally variable, and may involve multiple aquifers. Thus, the measurement of its magnitude and associated chemical fluxes is a challenging enterprise. A joint project of UNESCO and the International Atomic Energy Agency (IAEA) has examined several methods of SGD assessment and carried out a series of five intercomparison experiments in different hydrogeologic environments (coastal plain, karst, glacial till, fractured crystalline rock, and volcanic terrains). This report reviews the scientific and management significance of SGD, measurement approaches, and the results of the intercomparison experiments. We conclude that while the process is essentially ubiquitous in coastal areas, the assessment of its magnitude at any one location is subject to enough variability that measurements should be made by a variety of techniques and over large enough spatial and temporal scales to capture the majority of these changing conditions. We feel that all the measurement techniques described here are valid although they each have their own advantages and disadvantages. It is recommended that multiple approaches be applied whenever possible. In addition, a continuing effort is required in order to capture long-period tidal fluctuations, storm effects, and seasonal variations.

Tuberculosis outcome monitoring--is it time to update European recommendations?

We discuss tuberculosis treatment outcome monitoring and the adherence of countries in the WHO European Region to modifications introduced in 2001 to enhance inter-country comparability. Outcomes for definite pulmonary tuberculosis cases were compared for cases reported in 2001 and 2000. Reporting was considered complete if 98% or more of cases originally notified had outcome reported. In both years, maximal period of observation was 12 months from start of treatment. In 2000, countries reported outcome as 'cured', 'completed', 'died', 'failed', 'defaulted', 'transferred' and 'other, not evaluated' for cohorts of new and retreated cases. In 2001, following changes, countries were also requested to monitor cases with unknown treatment history and two outcome categories were added--'still on treatment' and 'unknown'. Of 42 countries reporting outcomes in 2001, 74% (31) had nationwide, complete data, up from 50% (19/38) in 2000. Twelve of 21 countries that reported on observation period complied with that recommended. 'Defaulted' and 'transferred' were applied interchangeably with 'unknown'. Among new cases, 'still on treatment' was used by 15/31 countries (range: 1%-15%). 'Failed' was rarely recorded in western European countries (<1%). European tuberculosis outcome monitoring should include all definite pulmonary cases, applying the standard period of observation and revised categories, and preferably reported using individual data.

Sample comminution for mycotoxin analysis: dry milling or slurry mixing?

A comparison was made between dry milling and slurry mixing as a comminuting step preceding mycotoxin analysis. Sample schemes of up to 30 kg are mandated by European Commission legislation. Cocoa, green coffee, almonds and pistachio samples of 10 kg were milled by a Romer analytical sampling mill and all three subsamples were analysed for aflatoxin B1 or ochratoxin A content. The homogenization process was evaluated in terms of the analytical results, coefficients of variation for different mills and particle size distributions. Coefficients of variation for the comminuting step were higher for dry milling than for slurry mixing. This difference was explained based on measured particle size distributions for both milling types. Measurements also showed slight differences in mycotoxin content of samples based on milling procedures. This might lead to lots being wrongly accepted or rejected based on an erroneous subsample result. It was concluded that sample comminution was best performed by slurry mixing, which produced smaller particles and, consequently, homogeneous samples with lowest coefficients of variation. Additional data are given on analytical results in 10-kg subsamples that originate from the aggregate 30-kg sample as described in Commission Directive 98/53/EC.

Molecular analysis of the sulfate reducing and archaeal community in a meromictic soda lake (Mono Lake, California) by targeting 16S rRNA, mcrA, apsA, and dsrAB genes.

Sulfate reduction is the most important process involved in the mineralization of carbon in the anoxic bottom waters of Mono Lake, an alkaline, hypersaline, meromictic Lake in California. Another important biogeochemical process in Mono Lake is thought to be sulfate-dependent methane oxidation (SDMO). However little is known about what types of organisms are involved in these processes in Mono Lake. Therefore, the sulfate-reducing and archaeal microbial community in Mono Lake was analyzed by targeting 16S rRNA, methyl-coenzyme M reductase (mcrA), adenosine-5'-phosphosulfate (apsA), and dissimilatory sulfite reductase (dsrAB) genes to investigate the sulfate-reducing and archaeal community with depth. Most of the 16S rRNA gene sequences retrieved from the samples fell into the delta-subdivision of the Proteobacteria. Phylogenetic analyses suggested that the clones obtained represented sulfate-reducing bacteria, which are probably involved in the mineralization of carbon in Mono Lake, many of them belonging to a novel line of descent in the delta-Proteobacteria. Only 6% of the sequences retrieved from the samples affiliated to the domain Euryarchaeota but did not represent Archaea, which is considered to be responsible for SDMO [Orphan et al. 2001: Appl Environ Microbiol 67:1922-1934; Teske et al.: Appl Environ Microbiol 68:1994-2007]. On the basis of our results and thermodynamic arguments, we proposed that SDMO in hypersaline environments is presumably carried out by SRB alone. Polymerase chain reaction (PCR) amplifications of the mcrA-, apsA-, and dsrAB genes in Mono Lake samples were, in most cases, not successful. Only the PCR amplification of the apsA gene was partially successful. The amplification of these functional genes was not successful because there was either insufficient "target" DNA in the samples, or the microorganisms in Mono Lake have divergent functional genes.

Displacement of the medial meniscus within the passive motion characteristics of the human knee joint: an RSA study in human cadaver knees.

The objective of this study was to validate an in vitro human cadaver knee-joint model for the evaluation of the meniscal movement during knee-joint flexion. The question was whether our model showed comparable meniscal displacements to those found in earlier meniscal movement studies in vivo. Furthermore, we determined the influence of tibial torque on the meniscal displacement during knee-joint flexion. Three tantalum beads were inserted in the medial meniscus of six human-cadaver joints. The knee joints were placed and loaded in a loading apparatus, and the movements of the beads were determined by means of RSA during knee-joint flexion and extension with and without internal tibial (IT) and external tibial (ET) torque. During flexion without tibial torque, all menisci moved in posterior and lateral direction. The anterior horn showed significantly greater excursions than the posterior horn in both posterior and lateral direction. Internal tibial torque caused an anterior displacement of the pathway on the tibial plateau. External tibial torque caused a posterior displacement of the pathway. External tibial torque restricted the meniscal displacement during the first 30 degrees of knee-joint flexion. The displacements of the meniscus in this experiment were similar to the displacements described in the in vivo MRI studies. Furthermore, the application of tibial torque confirmed the relative immobility of the posterior horn of the meniscus. During external tibial torque, the posterior displacement of the pathway on the tibial plateau during the first 30 degrees of flexion might be restricted by the attached knee-joint capsule or the femoral condyle. This model revealed representative meniscal displacements during simple knee-joint flexion and also during the outer limits of passive knee-joint motion.

Prosthetic replacement of the medial meniscus in cadaveric knees: does the prosthesis mimic the functional behavior of the native meniscus?

UNLABELLED: Meniscus replacement by a polymer meniscus prosthesis in dogs resulted in generation of new meniscal tissue. HYPOTHESIS: Optimal functioning of the prosthesis would involve realistic deformation and motion patterns of the prosthesis during knee joint motion. STUDY DESIGN: Controlled laboratory study. METHODS: The movements of the meniscus were determined during knee joint flexion and extension with and without internal and external tibial torque by means of roentgen stereophotogrammetric analysis. Subsequently, the meniscus in 6 human cadaveric knee joints was replaced by a meniscus prosthesis. RESULTS: All different parts of the meniscus showed a posterior displacement during knee joint flexion. The anterior horn was more mobile than the posterior horn. The prosthesis mimicked the movements of the meniscus. However, the excursions of the prosthesis on the tibial plateau were less. The knee joint laxity was not significantly higher after replacement with the meniscus prosthesis. CONCLUSIONS: The prosthesis approximated the behavior of the native meniscus. Improvement in both the gliding characteristics of the prosthetic material and the fixation of the prosthesis may improve the function. CLINICAL RELEVANCE: The meniscus prosthesis needs to be optimized to achieve a better initial function in the knee joint.

Contact investigations in congregate settings, New York City.

SETTING: Large urban tuberculosis control program. OBJECTIVE: To evaluate results of procedures implemented for systematic investigation of tuberculosis exposures in congregate settings. DESIGN: Between October 1995 and December 2000, a unit consisting of epidemiologists, health educators and tuberculin screening staff investigated exposures in sites with >15 persons. Transmission at the site was defined as likely, possible, unlikely or unknown. RESULTS: Among 100 investigations, 12 were tuberculosis case clusters, five were source case investigations, and 83 were exposures to single infectious cases. Transmission was likely in 24 (21%), possible in eight (8%), unlikely in 62 (62%), and could not be assessed in four (4%). Among the 83 exposures to single infectious cases, 2740 contacts were tested; 502 (18%) were infected. Among 1202 close contacts, 996 (82%) were tested, 197 (20%) were infected and started treatment of latent tuberculosis infection (LTBI) and 102/197 (52%) completed treatment. Sites with likely transmission had index patients with longer duration of cough (13 vs. 6 weeks, P = 0.01) and cavitary lesions (84% vs. 44%, P = 0.01) compared to sites with unlikely transmission. CONCLUSION: A systematic approach for conducting contact investigations in congregate settings is useful for assessing transmission. As such investigations are resource intensive and transmission is not common, performing tuberculin skin testing after most persons would have converted should be considered in low-risk groups. Additional efforts are needed to increase completion of treatment for LTBI in contacts identified in these settings.