An Experimental Assessment of Depth Estimation in Transparent and Translucent Scenes for Intel RealSense D415, SR305 and L515.

RGB-D cameras have become common in many research fields since these inexpensive devices provide dense 3D information from the observed scene. Over the past few years, the RealSense™ range from Intel® has introduced new, cost-effective RGB-D sensors with different technologies, more sophisticated in both hardware and software. Models D415, SR305, and L515 are examples of successful cameras launched by Intel® RealSense™ between 2018 and 2020. These three cameras are different since they have distinct operating principles. Then, their behavior concerning depth estimation while in the presence of many error sources will also be specific. For instance, semi-transparent and scattering media are expected error sources for an RGB-D sensor. The main new contribution of this paper is a full evaluation and comparison between the three Intel RealSense cameras in scenarios with transparency and translucency. We propose an experimental setup involving an aquarium and liquids. The evaluation, based on repeatability/precision and statistical distribution of the acquired depth, allows us to compare the three cameras and conclude that Intel RealSense D415 has overall the best behavior namely in what concerns the statistical variability (also known as precision or repeatability) and also in what concerns valid measurements.

Error Sources and Distinctness of Materials Parameters Obtained by THz-Time Domain Spectroscopy Using an Example of Oxidized Engine Oil.

Gasoline engine oil (SAE 5W-20) was subjected to thermal oxidization (TO) for four periods of time (0 h, 48 h, 96 h and 144 h) and exposed to THz-time domain spectroscopy (TDS) measurement. Error contributions from various error sources, such as repeatability errors, assembly errors of the probe volume and errors caused by the TDS system were evaluated with respect to discernibility and significance of measurement results. The most significant error source was due to modifications of the TDS setup, causing errors in the range of 0.13% of the refractive index for samples with a refractive index around 1.467 and a probe volume length between 5 and 15 mm at 1 THz. The absorption coefficient error was in the range of 8.49% for an absorption around 0.6 cm−1. While the average of measurements taken with different setup configurations did not yield significant differences for different TO times, a single, fixed setup would be able to discern all investigated oil species across the entire frequency range of 0.5⁻2.5 THz. The absorption coefficient measurement showed greater discernibility than the measurement of the refractive index.

Geo-Positioning Accuracy Improvement of Multi-Mode GF-3 Satellite SAR Imagery Based on Error Sources Analysis.

The GaoFen-3 (GF-3) satellite is the only synthetic aperture radar (SAR) satellite in the High-Resolution Earth Observation System Project, which is the first C-band full-polarization SAR satellite in China. In this paper, we proposed some error sources-based weight strategies to improve the geometric performance of multi-mode GF-3 satellite SAR images without using ground control points (GCPs). To get enough tie points, a robust SAR image registration method and the SAR-features from accelerated segment test (SAR-FAST) method is used to achieve the image registration and tie point extraction. Then, the original position of these tie points in object-space is calculated with the help of the space intersection method. With the dataset clustered by the density-based spatial clustering of applications with noise (DBSCAN) algorithm, we undertake the block adjustment with a bias-compensated rational function model (RFM) aided to improve the geometric performance of these multi-mode GF-3 satellite SAR images. Different weight strategies are proposed to develop the normal equation matrix according to the error sources analysis of GF-3 satellite SAR images, and the preconditioned conjugate gradient (PCG) method is utilized to solve the normal equation. The experimental results indicate that our proposed method can improve the geometric positioning accuracy of GF-3 satellite SAR images within 2 pixels.

Traceability of On-Machine Tool Measurement: A Review.

Nowadays, errors during the manufacturing process of high value components are not acceptable in driving industries such as energy and transportation. Sectors such as aerospace, automotive, shipbuilding, nuclear power, large science facilities or wind power need complex and accurate components that demand close measurements and fast feedback into their manufacturing processes. New measuring technologies are already available in machine tools, including integrated touch probes and fast interface capabilities. They provide the possibility to measure the workpiece in-machine during or after its manufacture, maintaining the original setup of the workpiece and avoiding the manufacturing process from being interrupted to transport the workpiece to a measuring position. However, the traceability of the measurement process on a machine tool is not ensured yet and measurement data is still not fully reliable enough for process control or product validation. The scientific objective is to determine the uncertainty on a machine tool measurement and, therefore, convert it into a machine integrated traceable measuring process. For that purpose, an error budget should consider error sources such as the machine tools, components under measurement and the interactions between both of them. This paper reviews all those uncertainty sources, being mainly focused on those related to the machine tool, either on the process of geometric error assessment of the machine or on the technology employed to probe the measurand.

[Trial sequential analysis : Sample size calculation for reliable meta-analyses]. / Sequenzielle Studienanalyse : "Fallzahlberechnung" für verlässliche Metaanalysen.

BACKGROUND: Meta-analyses have a great impact on medical decision-making. Random errors are, however, often the reason for misinterpretation of interventional effects in meta-analyses. OBJECTIVE: The aim of this article is to introduce authors and readers of meta-analyses to the problem of random errors. The article presents trial sequential analysis (TSA) as a suitable and user-friendly method that adjusts for the risk of random errors in meta-analyses. MATERIAL AND METHODS: The practical application of TSA is illustrated and exemplified using regional anesthesiology procedures versus conventional pain therapy with respect to the prevention of persistent postoperative pain after breast cancer surgery or thoracotomy. The results were compared with those from conventional meta-analytical methods. RESULTS: Conventional meta-analytical methods showed a significant advantage for patients after breast cancer surgery as well as after thoracotomy for regional anesthesia procedures with respect to the reduction of persistent postoperative pain. By means of TSA it could be concluded for thoracotomy that the evidence of this meta-analysis was sufficient. In contrast, the TSA for breast cancer surgery showed that based on the current data set and on the basis of relevant assumptions, it is potentially a false indication of an effect. There is currently no evidence that regional anesthesia leads to a significant reduction of persistent postoperative pain. CONCLUSION: The TSA is a suitable tool to minimize the risk of random errors and for a more reliable assessment of the evidence for the results of a meta-analysis.

An interlaboratory comparison program on ELF electric and magnetic fields measurements performed in Greece: Second round of the scheme.

The second round of an interlaboratory comparison program for extremely low frequency electric and magnetic fields measurements was performed at the High Voltage Laboratory of the National Technical University of Athens (Greece). The 16 participating laboratories measured the following: (i) electric field produced by a scale transmission line; (ii) magnetic field produced by a medium voltage cable; and (iii) magnetic field and frequency at the center of a standard square coil and their delivered results were evaluated in all measurement scenarios with use of performance statistics z-scores. Deviations between z-scores based on usual estimators (mean value, standard deviation) and robust estimators (derived with the robust algorithm described by the International Organization for Standardization [ISO, 2005]) highlight improved performance of the robust algorithm. An overall comparison to measurement procedure and performance results of the first round proves effectiveness and necessity of the scheme. Improper instrumentation or calibration, instability of the field source and measurement position uncertainty are factors that may cause unsatisfactory performance of the participants.

Analysis of Main Error Sources for the Error Motion Measurement of a Precision Shafting Using a T-Type Capacitive Sensor.

As a key indicator reflecting the working accuracy of rotary functional units, the error motions of the precision shafting are very necessary to be measured. In this paper, the main error sources for the error motion measurement of a precision shafting using a T-type capacitive sensor were investigated. The theoretical modeling error due to the approximate simplification for the output capacitance expressions was firstly analyzed. By means of the 3D-FEA method, the influence of fringe effects was subsequently investigated. Finally, the analysis of electrode installation errors was emphasized on the tilt error of the cylindrical electrode and coaxiality error of the fan-shaped electrode by establishing mathematical models and numerical simulation. Based on the theoretical analysis and simulation results, the methods of decreasing the approximate error and the nonlinear error caused by fringe effects were subsequently proposed; for the installation errors, the tilt error of cylindrical electrode only makes the solution of phase angle have a certain deviation and has almost no effect on solving the radial displacement, especially for the measurement range less than 0.1 mm; the measurement of the rotor tilt displacement was basically not affected by the coaxiality error of the fan-shaped electrode.

Guidewire simulation of endovascular intervention: A systematic review.

BACKGROUND: Endovascular intervention is an important minimally invasive surgery that requires professional skills to operate surgical instruments. Such skills are mainly gained through the traditional training paradigm of "see one, do one, teach one", rather than the guidewire simulation system. METHODS: To identify limitations of existing guidewire simulation research and suggest further research orientations, a comprehensive search on literature published from 2007 to 2021 is performed in 11 selected electronic databases. Through our scrutiny and filtration, 34 articles are selected as major studies for careful examinations. RESULTS: We identify challenges faced in the field of endovascular intervention guidewire simulation. We examine and classify guidewire simulation techniques (including guidewire models, collision detection methods and collision response methods), accuracy evaluation methods, error sources, and performance optimization methods. CONCLUSIONS: Guidewire simulation can satisfy the urgent need to train surgeons, thus more efforts should be dedicated enabling its wide application in clinical environment.

Radiomics analysis of EPID measurements for patient positioning error detection in thyroid associated ophthalmopathy radiotherapy.

PURPOSE: Electronic portal imaging detector (EPID)-based patient positioning verification is an important component of safe radiotherapy treatment delivery. In computer simulation studies, learning-based approaches have proven to be superior to conventional gamma analysis in the detection of positioning errors. To approximate a clinical scenario, the detectability of positioning errors via EPID measurements was assessed using radiomics analysis for patients with thyroid-associated ophthalmopathy. METHODS: Treatment plans of 40 patients with thyroid-associated ophthalmopathy were delivered to a solid anthropomorphic head phantom. To simulate positioning errors, combinations of 0-, 2-, and 4-mm translation errors in the left-right (LR), superior-inferior (SI), and anterior-posterior (AP) directions were introduced to the phantom. The positioning errors-induced dose differences between measured portal dose images were used to predict the magnitude and direction of positioning errors. The detectability of positioning errors was assessed via radiomics analysis of the dose differences. Three classification models-support vector machine (SVM), k-nearest neighbors (KNN), and XGBoost-were used for the detection of positioning errors (positioning errors larger or smaller than 3 mm in an arbitrary direction) and direction classification (positioning errors larger or smaller than 3 mm in a specific direction). The receiver operating characteristic curve and the area under the ROC curve (AUC) were used to evaluate the performance of classification models. RESULTS: For the detection of positioning errors, the AUC values of SVM, KNN, and XGBoost models were all above 0.90. For LR, SI, and AP direction classification, the highest AUC values were 0.76, 0.91, and 0.80, respectively. CONCLUSIONS: Combined radiomics and machine learning approaches are capable of detecting the magnitude and direction of positioning errors from EPID measurements. This study is a further step toward machine learning-based positioning error detection during treatment delivery with EPID measurements.

Performance Evaluation of Terrestrial Laser Scanners - A Review.

Terrestrial laser scanners (TLSs) are increasingly used in several applications such as reverse engineering, digital reconstruction of historical monuments, geodesy and surveying, deformation monitoring of structures, forensic crime scene preservation, manufacturing and assembly of engineering components, and architectural, engineering, and construction (AEC) applications. The tolerances required in these tasks range from few tens of millimeters (for example, in historical monument digitization) to few tens of micrometers (for example, in high precision manufacturing and assembly). With numerous TLS instrument manufacturers, each offering multiple models of TLSs with idiosyncratic specifications, it is a considerable challenge for users to compare instruments or evaluate their performance to determine if they meet specifications. As a result, considerable efforts have been made by research groups across the world to model TLS error sources and to develop specialized performance evaluation test procedures. In this paper, we review these efforts including recent work to develop documentary standards for TLS performance evaluation and discuss the role of these test procedures in establishing metrological traceability of TLS measurements.

Error and bias in determining exposure potential of children at school locations using proximity-based GIS techniques.

BACKGROUND: The widespread availability of powerful tools in commercial geographic information system (GIS) software has made address geocoding a widely employed technique in spatial epidemiologic studies. OBJECTIVE: The objective of this study was to determine the effect of the positional error in geocoding on the analysis of exposure to traffic-related air pollution of children at school locations. METHODS: For a case study of Orange County, Florida, we determined the positional error of geocoding of school locations through comparisons with a parcel database and digital orthophotography. We used four different geocoding techniques for comparison to establish the repeatability of geocoding, and an analysis of proximity to major roads to determine bias and error in environmental exposure assessment. RESULTS: RESULTS INDICATE THAT THE POSITIONAL ERROR IN GEOCODING OF SCHOOLS IS VERY SUBSTANTIAL: We found that the 95% root mean square error was 196 m using street centerlines, 306 m using TIGER roads, and 210 and 235 m for two commercial geocoding firms. We found bias and error in proximity analysis to major roads to be unacceptably large at distances of < 500 m. Bias and error are introduced by lack of positional accuracy and lack of repeatability of geocoding of school locations. CONCLUSIONS: These results suggest that typical geocoding is insufficient for fine-scale analysis of school locations and more accurate alternatives need to be considered.

Error and discrepancy in radiology: inevitable or avoidable?

Errors and discrepancies in radiology practice are uncomfortably common, with an estimated day-to-day rate of 3-5% of studies reported, and much higher rates reported in many targeted studies. Nonetheless, the meaning of the terms "error" and "discrepancy" and the relationship to medical negligence are frequently misunderstood. This review outlines the incidence of such events, the ways they can be categorized to aid understanding, and potential contributing factors, both human- and system-based. Possible strategies to minimise error are considered, along with the means of dealing with perceived underperformance when it is identified. The inevitability of imperfection is explained, while the importance of striving to minimise such imperfection is emphasised. TEACHING POINTS: • Discrepancies between radiology reports and subsequent patient outcomes are not inevitably errors. • Radiologist reporting performance cannot be perfect, and some errors are inevitable. • Error or discrepancy in radiology reporting does not equate negligence. • Radiologist errors occur for many reasons, both human- and system-derived. • Strategies exist to minimise error causes and to learn from errors made.

Experts confer on vasectomy and prostate cancer risk.

PIP: In March 1993, physicians attended a US National Institutes of Health (NIH) conference on a possible association between vasectomy and prostate cancer. Participants learned that some studies have found an association while others have not. The strongest evidence of an association is a small association. The inconsistency of the results of various studies and the lack of a convincing biological mechanism satisfied participants that no need exists to recommend changes in clinical and public health practice. 2 recent, well-controlled studies, conducted by researchers at Brigham and Women's Hospital in Boston, Massachusetts, published in the Journal of the American Medical Association found around a 60% increase in risk of developing prostate cancer in men with vasectomies. It found a decreased risk for overall mortality among vasectomized men, however. These studies prompted a call for this NIH conference. Studies prior to these Boston studies had methodological flaws, especially detection bias. Specifically, urologists are more likely to examine men with vasectomies and, therefore, diagnose prostate cancer. A well-controlled, large-scale, case control study in California published in 1991 and its follow-up study did not find an increased risk of prostate cancer in vasectomized men. The follow-up study found a decreased risk for overall mortality among men with vasectomies. The lack of knowledge about the etiology of prostate cancer is the biggest roadblock to understanding the link between vasectomy and prostate cancer. Suggested mechanisms explaining vasectomy's ability to increase prostate cancer risk include changes in hormone levels, immunologic responses, and changes in levels of cancer-promoting growth factors or inhibitors of these factors.^ieng

Induced abortion and risk for breast cancer: reporting (recall) bias in a Dutch case-control study.

BACKGROUND: In general, no association has been found between spontaneous abortion (naturally occurring termination of a pregnancy) and the risk for breast cancer. With respect to induced abortion (termination of a pregnancy by artificial means), the results have been more inconclusive. A positive association was found in five studies, no association was found in six studies, and a negative association was found in the only cohort study. It is thought that part of the inconsistency of the reported results may be attributable to reporting (recall) bias, since all but two studies on induced abortion used the case-control design and were based only on information obtained from study subjects. In comparison with breast cancer case patients, healthy control subjects may be more reluctant to report on a controversial, emotionally charged subject such as induced abortion. Thus, differential underreporting may be a cause of spurious associations in case-control studies. PURPOSE: Our goal was threefold: 1) to evaluate the relationship between a history of induced or spontaneous abortion and the risk for breast cancer in a Dutch population-based, case-control study; 2) to examine reporting bias by comparing risks between two geographic areas (i.e., western regions and southeastern regions in The Netherlands that differ in prevalence of and attitudes toward induced abortion); and 3) to compare reporting bias in data on induced abortion with reporting bias in data on oral contraceptive use. METHODS: Data analyzed in this study were obtained from 918 women (20-54 years of age at diagnosis) who were diagnosed with invasive breast cancer during the period from 1986 through 1989 and had been initially enrolled in a population-based, case-control study investigating oral contraceptive use and breast cancer risk. The women resided in one of four geographic areas that were covered by Regional Cancer Registries: two western regions (Amsterdam and West) and two southeastern regions (East and Eindhoven). Each case patient was pair-matched, on the basis of age (within 1 year) and region, with a control subject who was randomly selected from municipal registries that fully covered the Dutch population. Both the case patients and the control subjects were interviewed at home by the same trained interviewer, who used a structured questionnaire. Reporting bias was examined indirectly by comparing risks between the western and the southeastern regions of the country, which differ in the prevalence of and attitude toward induced abortion. Multivariate conditional logistic regression methods for individually matched case-control studies were used to estimate relative risks (RRs). Reported P values are two-sided. RESULTS AND CONCLUSION: Among parous women, a history of induced abortion was associated with a 90% increased risk for breast cancer (adjusted RR = 1.9; 95% confidence interval [CI] = 1.1-3.2). Among nulliparous women, no association between induced abortion and breast cancer was found. Neither among parous women nor among nulliparous women was a history of spontaneous abortion related to the risk for breast cancer. The association between induced abortion and breast cancer was stronger in the southeastern regions of the country, which have a predominantly Roman Catholic population, than in the western regions (adjusted RR = 14.6 [95% CI = 1.8-120.0] versus adjusted RR = 1.3 [95% CI = 0.7-2.6], respectively; test of difference between regions, P = .017), suggesting reporting bias. Support for reporting bias as an explanation for the regional differences was also found in data supplied by both study subjects and their physicians on the use of oral contraceptives. In comparison with physicians, control subjects in the southeastern regions underreported the duration of their oral contraceptive use by 6.3 months more than control subjects in the western regions (P = .007)...

PIP: Data were analyzed from 918 women aged 20-54 years at diagnosis with invasive breast cancer during 1986-89. The women had initially enrolled in a population-based, case-control study investigating oral contraceptive use and the risk of breast cancer. Each case was pair-matched according to age and region of residence, and cases and controls interviewed at home. Among parous women, a history of induced abortion was associated with a 90% increased risk of breast cancer. Among nulliparous women, no association was found between induced abortion and breast cancer. Neither among parous women nor nulliparous women was a history of spontaneous abortion related to the risk of breast cancer. The association between induced abortion and breast cancer was stronger in the southeastern regions of the country, where there is a predominantly Roman Catholic population, suggesting reporting bias. Support for reporting bias as an explanation for regional differences was also found in data supplied by study participants and their physicians on the use of oral contraception. The authors conclude that reporting bias is a real problem in case-control studies of induced abortion and breast cancer risk if study findings are based solely upon information from study subjects.

Her-2/neu and INT2 proto-oncogene amplification in malignant breast tumors in relation to reproductive factors and exposure to exogenous hormones.

In previous studies in southern Sweden, early use of oral contraceptives has been found to be accompanied by an increased risk of developing premenopausal breast cancer, and the tumors developing in these patients have shown a more aggressive behavior. In the present study, amplification of the proto-oncogenes Her-2/neu (also known as ERBB2) and INT2 was studied in primary tumor specimens from 72 premenopausal women and was related to starting age of oral contraceptive use and other reproductive risk factors. Amplification of Her-2/neu was more common among early oral contraceptive users (i.e., those starting at less than or equal to 20 years of age) than among nonusers or late users (odds ratio [OR], 5.3; 95% confidence interval [CI], 1.6-16.7), whereas INT2 amplification did not differ significantly among those groups (OR, 0.9; 95% CI, 0.1-5.0). The likelihood of INT2 amplification was greater among users of progestins and those with a history of abortions before the first full-term pregnancy (OR, 9.0; 95% CI, 1.3-51.7; and OR, 18.6; 95% CI, 2.2-165.8, respectively). No significant relationships were found between proto-oncogene amplification and the variables of parity, age at first full-term pregnancy, or late abortion. The increased ORs persisted after adjustment for age at diagnosis and other risk factors. The findings suggest that the higher rate of Her-2/neu amplification among early oral contraceptive users is an effect of the oral contraceptive use per se rather than of the relative youth of the users. Moreover, the relationship between progestin use and early abortion and amplification of the INT2 gene is biologically plausible.

Vector velocity volume flow estimation: Sources of error and corrections applied for arteriovenous fistulas.

A method for vector velocity volume flow estimation is presented, along with an investigation of its sources of error and correction of actual volume flow measurements. Volume flow errors are quantified theoretically by numerical modeling, through flow phantom measurements, and studied in vivo. This paper investigates errors from estimating volumetric flow using a commercial ultrasound scanner and the common assumptions made in the literature. The theoretical model shows, e.g. that volume flow is underestimated by 15%, when the scan plane is off-axis with the vessel center by 28% of the vessel radius. The error sources were also studied in vivo under realistic clinical conditions, and the theoretical results were applied for correcting the volume flow errors. Twenty dialysis patients with arteriovenous fistulas were scanned to obtain vector flow maps of fistulas. When fitting an ellipsis to cross-sectional scans of the fistulas, the major axis was on average 10.2mm, which is 8.6% larger than the minor axis. The ultrasound beam was on average 1.5mm from the vessel center, corresponding to 28% of the semi-major axis in an average fistula. Estimating volume flow with an elliptical, rather than circular, vessel area and correcting the ultrasound beam for being off-axis, gave a significant (p=0.008) reduction in error from 31.2% to 24.3%. The error is relative to the Ultrasound Dilution Technique, which is considered the gold standard for volume flow estimation for dialysis patients. The study shows the importance of correcting for volume flow errors, which are often made in clinical practice.

Patient cueing, a type of diagnostic error.

Diagnostic failure can be due to a variety of psychological errors on the part of the diagnostician. An erroneous diagnosis rendered by previous clinicians can lead a diagnostician to the wrong diagnosis. This report is the case of a patient who misdiagnosed herself and then led an emergency room physician and subsequent treating physicians to the wrong diagnosis. This mechanism of diagnostic error can be called patient cueing.

Rapid and simple screening and supplemental testing for HIV-1 and HIV-2 infections in west Africa.

OBJECTIVE: To evaluate a combination of rapid tests as a strategy for screening and supplemental testing of serum for HIV-1 and/or HIV-2 antibodies. DESIGN: Cross-sectional evaluation. SETTING: Projet RETRO-CI, an AIDS research project in Abidjan, Côte d'Ivoire. METHODS: Serum specimens were collected from 1000 consecutive women giving birth in an Abidjan maternal and child health centre and from 185 hospitalized patients. All serum specimens were tested for HIV-1 and HIV-2 antibodies by whole-virus enzyme immunoassay; repeatedly reactive specimens were further tested by virus-specific Western blot and synthetic peptide-based tests. This was the reference strategy against which the algorithm under evaluation was compared. All specimens were subsequently tested by a mixed (HIV-1 and HIV-2) recombinant antigen-based test (Abbott Testpack), followed, if positive, by a rapid synthetic peptide-based test (Genetic Systems Genie) as a supplemental test. RESULTS: According to the reference strategy the prevalence of HIV-1 and/or HIV-2 infection was 13% among the pregnant women and 78% among the hospitalized patients. Compared with the reference strategy, the combination of rapid tests was associated with a sensitivity of 99.6%, a specificity of 99.9%, and positive and negative predictive values of 99.6 and 99.9%, respectively. Four per cent of HIV-2-positive and 1% of HIV-1-positive specimens were considered dually reactive by the rapid test combination. CONCLUSIONS: Synthetic peptide-based tests provide an alternative to Western blots for supplemental testing for HIV-1 and HIV-2. This combination of rapid tests offers performance characteristics comparable to an enzyme immunoassay and Western blot-based strategy, without requiring running water, electricity, or a well-developed laboratory. High-quality serodiagnosis of HIV-1 and HIV-2 infections is possible at the most peripheral levels of the health-care system in developing countries, the limiting factors being the costs of tests and training of staff.

PIP: Researchers from an AIDS research project took blood samples from 1000 consecutive women during childbirth at a maternal and child health center in Abidjan, Cote d'Ivoire, and from 185 hospitalized patients to compare the results of a combination of synthetic peptide-based rapid tests (product names, Testpack and Genie), which check for HIV-1 and HIV-2 antibodies, with those of the Western Blot-based test. They also wanted to see whether the rapid test-based strategy could replace the Western Blot-based test as a supplemental test. The Western Blot indicated the HIV-1 and/or HIV-2 prevalence to be 13% among the new mothers and 78% among the hospitalized patients for an overall prevalence of 23%. 3.3% of all people were positive for both HIV-1 and HIV-2. 17.4% tested positive for just HIV-1. 2.1% were positive for HIV-2. The rapid tests had a sensitivity of 99.6% and a specificity of 99.9%. The positive predictive value was 99.6% and the negative predictive value was 99.9%. The rapid tests identified 4% of the HIV-2 positive samples and 1% of the HIV-1 samples to be dually reactive. These findings demonstrated that rapid synthetic peptide-based assays reliably detect HIV-1 and HIV-2 antibodies and can be supplemental tests. High quality HIV serology can be performed in a setting without running water and electricity which was the case in this study. A further advantage of this strategy is that each test takes only 10 minutes. These tests would have significant effects on HIV testing and counseling, diagnosis, and screening of blood for transfusion in rural areas of developing countries.

Estimating the incubation period of paediatric AIDS in Rwanda.

OBJECTIVE: To estimate the distribution of the incubation period of paediatric AIDS in Rwanda. DESIGN: Data were collected between February 1984 and December 1990 at the Centre Hospitalier de Kigali (CHK), the capital city of Rwanda, Central Africa. PATIENTS: We used a sample of 685 AIDS cases registered consecutively in the Department of Paediatrics of the CHK, in which the proportion of perinatally acquired HIV-1 infection was estimated to be 98.6%. METHODS: We performed both non-parametric and parametric analyses. The methods of estimation were adapted to truncated data, using essentially the same methods as Auger et al. in their analysis of data from the New York City and the New York State AIDS case registries in 1988. RESULTS: We found that a double Weibull model fitted the data very well and that the risk of developing AIDS was high for subjects under 18 months of age, but lower for older subjects. CONCLUSIONS: Our results were qualitatively similar to those of Auger et al.. There were quantitative differences between the two studies, but it was not possible to compare median survival periods. Parameters such as median or mean survival times cannot be validly estimated using only data from registers because these data exclude infected subjects who have not yet developed AIDS.

PIP: The authors used nonparametric and parametric methods and data on 685 AIDS cases at the Centre Hospitalier de Kigali, collected between February 1984 and December 1990, to estimate the distribution of pediatric AIDS in Kigali, Rwanda. 98.6% of the cases probably acquired AIDS via vertical transmission. A combination of the 2 Weibul distributions (parametric method) resulted in a good fit, suggesting that the sample population consisted of a subpopulation with a short incubation period and an other with a longer incubation period. The researchers could not deduce proof of heterogeneity from the shape of the distribution, however. The probability of developing AIDS during the first year of life was 0.29, which corresponded with that of the European Collaborative Study (0.26). The risk of developing pediatric AIDS increased considerably for children less than 18 months old but fell and became constant for older children. The qualitative findings matched those of a study in New York City. Even though quantitative differences between this study and the other study existed, the researchers could not compare median survival times. Since data from registers did not include HIV-infected children who had not yet developed AIDS, the researchers were not able to estimate median and mean survival periods. A possible source of bias was that the data were from a surveillance system based on cases at just 1 hospital, which probably did not see all pediatric AIDS cases. In conclusion, truncated data determined rather well the distribution of incubation periods, but could not provide much information about the scale parameters of the model.

Evaluation of two staging systems for HIV infection for use in developing countries.

OBJECTIVE: To evaluate the clinical axis of the World Health Organization (WHO) clinical staging system and the modified WHO staging system proposed by Montaner et al. using the lymphocyte strata > 1500, 1500-1000 and < 1000 cells x 10(6)/l. DESIGN: Cross-sectional study. PATIENTS: Four hundred and fifteen consecutive patients with HIV infection attending three HIV reference centres in Belgium. METHODS: Absolute CD4 lymphocyte counts were compared between stages within the two staging systems. RESULTS: Median CD4 lymphocyte counts decreased with increasing stage of disease in both staging systems. Differences in median CD4 lymphocyte counts between stages of each staging system were statistically significant (Kruskal-Wallis one-way analysis of variance, P < 0.001). The WHO clinical stage 1 and the modified WHO stage I had positive predictive values of 56 and 58%, respectively, for identifying patients with CD4 lymphocyte levels > 500 cells x 10(6)/l. The WHO clinical stage 4 and the modified WHO stage IV had positive predictive values of 79 and 80%, respectively, for identifying patients with CD4 lymphocyte levels < 200 cells x 10(6)/l. CONCLUSIONS: The WHO clinical staging system or a modified version of this system using lymphocytes stratification may be a good alternative in developing countries to the CD4 lymphocyte count-based HIV staging system used in the developed world. Cohort studies in developing countries are needed to assess their prognostic value.

PIP: In 1990, Belgium, physicians enrolled 415 consecutive patients attending HIV reference centers in Antwerp, Brussels, and Ghent in a cross-sectional study designed to evaluate the clinical axis of the WHO staging system with and without the lymphocyte stratification proposed by Montaner el al. (that is, modified WHO staging system) (1500, 1500- 1000, and 1000 cells x 1 million/l). They filled in a standardized questionnaire with all criteria of the WHO staging system. Laboratory personnel used standard hematology and flow cytometry techniques to determine absolute and CD4 lymphocyte counts. 80% of the patients were Caucasians. 46% of all patients were homosexual and 42% were heterosexual; 79.2% were men. Median CD4 lymphocyte counts fell in both staging systems as the stage of HIV infection increased. There were significant differences in median CD4 counts between stages of each staging system (p .001). The modified WHO staging system's stage I was more sensitive at identifying patients with CD4 lymphocyte counts of more than 500 cells x 1 million/l than the WHO clinical stage 1 (83% sensitivity vs. 48% sensitivity). The positive predictive value of WHO clinical stage 4 and of the modified WHO staging system's stage IV for identifying people with CD4 lymphocyte counts of less than 200 cells x 1 million/l was quite high (79% and 80%, respectively). The researchers suggested that clinicians use stages 4 and IV as end-points is clinical trials in developing countries. Clinicians completing the questionnaire knew the patients' earlier CD4 lymphocyte count, which may have introduced a bias in the study. For example, they may have more thoroughly examined patients with low CD4 lymphocyte counts than those with normal counts. Nevertheless, the study's results indicated that either one of these systems may be a good alternative in developing countries to the technical equipment-dependent CD4 lymphocyte count-based HIV staging system used in developed countries. Cohort studies in developing countries would evaluate their prognostic value.