Biomedical subjects
Publications and source records attributed to A Hadgu.
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OBJECTIVES: This analysis describes trends in the prevalence of genital chlamydial infection in economically disadvantaged young women entering a national job training program. METHODS: We examined chlamydia test data for May 1990 through June 1997 for women aged 16 to 24 years who enrolled in the program. The significance of trends was evaluated with the chi 2 test for trend. RESULTS: Prevalence of chlamydial infection declined 32.9%, from 14.9% in 1990 to 10.0% in 1997 (P < .001). Prevalence decreased significantly in all age groups, racial/ethnic groups, and geographic regions. CONCLUSIONS: The decrease in prevalence of chlamydial infection suggests that prevention activities have reached disadvantaged women across the United States; however, prevalence of chlamydial infection remains high, and enhanced prevention efforts in disadvantaged communities are urgently needed.
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Discrepant analysis is a widely used technique for estimating test performance indices (sensitivity, specificity, etc.) of DNA-amplification tests for detecting infectious diseases. It has recently been claimed that the discrepant analysis-based estimates of specificity are typically less biased than those based on culture and that the discrepant analysis-based specificity shows little appreciable bias. In this article, I show that those conclusions are incorrect. Using a typical example from the published literature, I show that the discrepant analysis-based estimates of sensitivity and specificity can generate a significant and clinically important overestimation of the true sensitivity and specificity values. Moreover, I demonstrate that the concept of discrepant analysis is profoundly flawed and unscientific. It violates a fundamental principle of diagnostic testing-the principle that the new test should not be used to determine the true disease status. Thus, the major problem with discrepant analysis is not only that it is biased but that it is unscientific. Therefore, discrepant analysis should not be adopted for the evaluation of any diagnostic or screening test.
Longitudinal data present statistical problems of interest in clinical trials and epidemiologic studies. In this article, we consider a dental clinical trial in which the outcome measurements are taken on each subject at two follow-up times, and the primary interest is in the dependence of the outcome variable on covariates. The common data structure of these studies is the presence of an intraclass or serial correlation within primary sampling units or subjects. Recently generalized linear models have had extensions to methods for generalized estimating equations that take correlations within primary sampling units into account. We review and apply the Liang-Zeger methodology to a dental clinical trial. In this study, 109 adult male and female volunteers with pre-existing dental plaque were randomized to two mouth rinses (A and B) or a control mouth rinse with double blinding. The major research question in this analysis was: Are the two experimental mouth rinses more effective than the control mouth rinse in inhibiting the development of dental plaque? And if so, what is the effect of baseline plaque measurement?
Nucleic acid amplification tests offer superior sensitivity for the detection of Chlamydia trachomatis infection, but many laboratories still use nonamplification methods because of the lower cost and ease of use. In spite of their availability for more than a decade, few studies have directly compared the nonamplification tests. Such comparisons are still needed in addition to studies that directly compare individual nonamplification and amplification tests. The purpose of this study was to evaluate and compare the performance characteristics relative to culture of five different tests for the detection of C. trachomatis with and without confirmation of positive results. The tests were applied to endocervical specimens from 4,980 women attending family planning clinics in the northwestern United States. The five nonculture tests included Chlamydiazyme (Abbott), MicroTrak direct fluorescent antibody (DFA) (Syva), MicroTrak enzyme immunoassay (EIA) (Syva), Pace 2 (Gen-Probe), and Pathfinder EIA (Sanofi/Kallestad). All positive results obtained with a nonculture test (except MicroTrak DFA) were confirmed by testing the original specimens with a blocking antibody test (Chlamydiazyme), a cytospin DFA (MicroTrak EIA and Pathfinder EIA), and a probe competition assay (Pace 2). The prevalence of culture-proven chlamydia was 3.9%. The sensitivities of the nonculture tests were in a range from 62 to 75%, and significant differences between tests in terms of sensitivity were observed. The positive predictive value for each test was 0.85 or higher. The specificities of the nonculture tests without performance of confirmations were greater than 99%. Performing confirmatory tests eliminated nearly all of the false positives.
OBJECTIVE: To study infectious pathology at index ectopic pregnancy and to determine what other factors predispose a woman to repeat ectopic pregnancy. METHODS: All women (n = 697) with their first (index) ectopic pregnancy histologically verified between January 1, 1978, and December 31,1993, at the only two hospitals in one Norwegian county were eligible. Included were permanent residents of the county who were 37 years of age or younger and who had not had tubal surgery before the index pregnancy. When the study closed on November 1, 1994, the participants had been observed prospectively for fertility events from approximately 1 to 17 years. Included in the final analyses were 353 women who had from one to five natural conceptions, for a total of 555 pregnancies. Chi-square test was used in univariate analysis, and the generalized estimating equations approach was used to analyze correlated responses and covariates that changed over time. RESULTS: Pregnancy order is the stronger correlate of subsequent ectopic pregnancy. The frequency of repeat ectopic pregnancy decreased by one-third for each pregnancy from the first to the third pregnancy. The odds of having another ectopic pregnancy were nearly three times higher for women with a diagnosis of infectious pathology than for women who had no infectious pathology. Other correlates of repeat ectopic pregnancy include age 24 years or younger at first ectopic pregnancy, history of repeat ectopic pregnancy, initiation of infertility work-up, and conception with an intrauterine device at index pregnancy. Method of surgery was not associated with repeat ectopic pregnancy. CONCLUSION: The most crucial reproductive event after first ectopic pregnancy is the first event to occur. Women who have experienced two ectopic pregnancies should be considered candidates for assisted reproduction.
This work is motivated by a longitudinal study of women and their ectopic pregnancy outcomes in Lund, Sweden. In this article, we review and apply the Liang-Zeger methodology to the Lund ectopic pregnancy data set. We further analyse the ectopic pregnancy data using conditional modelling approaches suggested by Rosner and Bonney. From the Lund ectopic pregnancy data, we learned that PID is the strongest predictor of subsequent development of ectopic pregnancy and that there is a monotone relationship between PID severity and ectopic pregnancy. We also learned that the presence of mycoplasma from lower or upper genital tract sites at index laparoscopy is also a strong predictor of ectopic pregnancy. Other correlates of ectopic pregnancy include age at pregnancy and history of gynaecologic surgery.
The purpose of this paper is to show that the sensitivity and specificity estimates obtained by 'discrepant analysis' are biased. Discrepant analysis is a widely used technique that attempts to provide estimates of sensitivity and specificity in the presence of an imperfect gold standard. Many researchers have applied this technique to estimate the sensitivity and specificity of DNA-amplification tests for Chlamydia trachomatis such as the plasmid based ligase chain reaction (LCR) and polymerase chain reaction (PCR) tests. Moreover, the June 1993 package insert of the PCR AMPLICOR Chlamydia trachomatis test contains estimates of sensitivity and specificity based on 'discrepant analysis'. Even if one employs a perfect test to resolve the discrepant results, discrepant analysis estimates of test sensitivity and specificity remain biased. Thus, one should not adopt this technique to evaluate the performance of a diagnostic test.
AIMS: To evaluate demographic characteristics of women terminating their pregnancy for sentinel surveillance of Chlamydia trachomatis infection and to report changing prevalences of C trachomatis over time within this study population. DESIGN: Screening for C trachomatis in women seeking induced abortion was introduced in 1984 at the Department of Gynecology, Regional Hospital, Trondheim, Norway. Over the study years our department has used a precoded medical record covering sociodemographic, medically relevant data, also recording outcome of the C trachomatis test. Throughout the study the Department of Microbiology applied cell culture, enzyme immunoassay, and, during the most recent years a nucleic acid test to identify C trachomatis. STATISTICAL METHODS: Chi square test for linear trend and unconditional logistic regression. RESULTS: Over the study period, women having induced abortion were characterised by being most often single and more often at younger age. The overall age-adjusted prevalence of C trachomatis declined from 9.2% in 1985 to 3.6% in 1995, the major decline occurring from 1987 to 1991, and affected all age-groups simultaneously. There was a 60% decrease in odds ratio of having a C trachomatis infection from 1985 to 1991, and the crude and the adjusted odds ratios did not differ for any year examined. CONCLUSION: Women deciding on pregnancy termination have demographic characteristics that identify high-risk groups for C trachomatis infection. Despite these characteristics, which were relatively constant over the study period, the study population changed from being a high- to a low-prevalence population of C trachomatis.
OBJECTIVES: The purpose of this analysis was to derive potential gonorrhea screening criteria for women. METHODS: Data corresponding to 44,366 gonorrhea cultures from women 15 through 44 years of age in Columbus, Ohio, were analyzed. RESULTS: Characteristics that were associated with gonococcal infection and were suitable for screening decisions included patient's age and marital status and previous prevalence of gonorrhea at provider site. Probabilities of infection ranged from .001 for married women 25 through 44 years of age at low-prevalence provider sites to .078 for unmarried women 15 through 19 years of age at high-prevalence sites. CONCLUSIONS: Patient's age and marital status and prevalence of gonorrhea at provider site can be used as indicators to ensure testing of high-prevalence groups.
Discrepant analysis is a widely used technique that attempts to provide estimates of sensitivity and specificity in the presence of an imperfect gold-standard. This technique has been applied by many researchers to estimate the sensitivity and specificity of DNA-amplification tests for Chlamydia trachomatis such as the plasmid-based ligase chain-reaction and polymerase chain-reaction tests. However, the sensitivity and specificity estimates obtained by discrepant analysis are upwardly biased, and this bias remains even when a perfect test is used to resolve the discrepant results. This technique should not be adopted for evaluating the performance of a diagnostic test.
A general estimating equation approach is used to obtain estimates of sensitivity and specificity when the data consist of correlated binary outcomes. First order approximations to the variances of estimated sensitivity and specificity for prospective and retrospective studies are given. Data from a dental study are used to motivate and illustrate the methods.
Four hundred and fifty patients were enrolled into a randomised clinical trial in a public sexually transmitted diseases clinic to evaluate the efficacy of podophyllin, cryotherapy, and electrodesiccation for treatment of external genital warts. Complete clearance of warts was observed in 41%, 79%, and 94% of patients who received up to six weekly treatments of podophyllin, cryotherapy, and electrodesiccation, respectively. Relapses occurred in 25% of all patients, yielding 3 month clearance rates of 17%, 55%, and 71% for podophyllin, cryotherapy, and electrodesiccation, respectively. Wart volume and duration did not influence treatment outcome. Response to therapy was greater in women than in men, and did not differ by treatment modality. Electrodesiccation and cryotherapy were more effective than podophyllin for the treatment of external genital warts, but none of these three treatments were highly successful.
To examine the validity of cervical cytologic diagnosis of sexually transmitted diseases, we reviewed the literature and calculated the efficacy of the Papanicolaou smear as a diagnostic technique. The predictive value of a positive test varied widely, but was generally higher for Trichomonas vaginalis (0.81-1.00) than for other organisms. For Chlamydia trachomatis, the predictive value of a positive test ranged from 0.40-1.00. Cytologic diagnosis of sexually transmitted diseases has not been studied adequately, but the available literature suggests that its sensitivity is low. In general, the Papanicolaou smear should not be used to diagnose sexually transmitted diseases, and treatment should not be based on cytologic findings alone. At best, cytologic indications of sexually transmitted diseases should prompt a definitive laboratory test.
A multivariate logistic regression analysis of patient symptoms and signs and laboratory findings associated with the diagnosis of acute pelvic inflammatory disease was performed with use of data from 628 women who were clinically diagnosed as having the disease for the first time at the University of Lund, Sweden. In 414 women (65.9%) acute pelvic inflammatory disease was laparoscopically confirmed. We developed a mathematical model that correctly predicted 87.0% of the cases of acute pelvic inflammatory disease and had an overall correct classification rate of 75.6%. Variables that were good predictors of acute pelvic inflammatory disease were purulent vaginal discharge, erythrocyte sedimentation rate greater than or equal to 15 mm/hr, positive gonorrhea result, adnexal swelling on bimanual examination, and rectal temperature greater than or equal to 38 degrees C. Furthermore, we developed "mixed model I" and "mixed model II," which combine simple clinical parameters and laparoscopy in varying degrees. In mixed model I the sensitivity, specificity, and overall classification values were 93%, 67.2%, and 84.5%; in mixed model II these values were 100%, 67.2%, and 89.2%. Use of relatively simple and reproducible clinical parameters can identify those women who would most benefit from laparoscopy to diagnose acute pelvic inflammatory disease.
We provide a brief summary of the theory of ridge regression, regress reported rates of congenital syphilis on three stages of adult syphilis using both ridge regression and least squares techniques, and discuss the results. We also develop a principal components regression model for the same example and compare the results. The example demonstrates the usefulness of ridge regression to handle multicollinearity in data. Problems of overestimation and instability associated with ordinary least squares estimates of these non-orthogonal data diminish with use of the ridge regression techniques.
A generalized estimating equation (GEE) approach is used to estimate the sensitivity and specificity of five non-culture screening tests for detecting Chlamydia trachomatis in endocervical specimens from women attending family planning clinics. Since the estimates of these parameters can be very close to the upper limit of one, confidence interval construction based on the traditional approaches, such as the delta method or a back-transformation approach, may not have the stated coverage. We compare different approaches to calculating confidence intervals for the sensitivity and specificity from the results of the GEE approach. These methods include the delta method, a back-transformation approach, and a bootstrap approach. In addition, we use simulations to investigate the estimated coverage rates of the delta method and the back-transformation approach. Published in 2001 by John Wiley & Sons, Ltd.