Interpretation of the tuberculin skin test.

Objective: To reinterpret epidemiologic information about the tuberculin test (purified protein derivative) in terms of modern approaches to test characteristics; to clarify why different cutpoints of induration should be used to define a positive test in different populations; and to calculate test characteristics of the intermediate-strength tuberculin skin test, the probability of Mycobacterium tuberculosis infection at various induration sizes, the area under the receiver operating characteristic (ROC) curve, and optimal cutpoints for positivity.

Methods: Standard epidemiologic assumptions were used to distinguish M. tuberculosis-infected from -uninfected persons; also used were data from the U.

In vitro glycolysis of whole blood can detect primed neutrophils in septic ICU patients.

The purpose of this study was to develop a bedside assay based on the in vitro glycolysis of a whole blood sample that could detect primed neutrophils (PMNs). A mathematical index of the PMN response to exogenous stimulation with phorbol myristate 13-acetate (PMA), called the Delta value, was derived by comparing the increase in glycolysis for paired blood samples with and without PMA to that expected from normal subjects. Delta values for systemic inflammatory response syndrome/sepsis patients (9.

Mixed venous O2 saturation: measured by co-oximetry versus calculated from PVO2.

Objective: The objectives of our study were (1) to compare mixed venous saturations calculated by a blood gas machine with those measured directly by a co-oximeter; and (2) to compare the sensitivities and specificities of VO2s derived from these values.

Methods: Charts were retrospectively reviewed of all MICU patients [n = 16] between December 1, 1991 and January 31, 1992, who required pulmonary artery catheters for their usual care and who had hemoglobin saturations of mixed venous blood concurrently measured by both a co-oximeter (Co-Ox Model 482, Instrumentation Lab, Lexington, MA) and a blood gas analyzer (Nova Biomedical StatLab5, Waltham, MA) which uses a variant of the Severinghaus equation to calculate SVO2 from PVO2). Data used at the time of each SVO2 measurement to calculate oxygen consumption (VO2) further was collected.

Compliance in the care of disposable contact lenses: the effect of patients' health beliefs.

We used Becker and Maiman's Health Belief Model to study the compliance of 100 disposable contact lens patients using a recommended lens care routine. Compliance was defined as continuous lens wear for no more than two consecutive weeks. A telephone survey found 90 of 100 patients to be complaint.

Decision analysis in formulary decision making.

Although decision making about what drugs to include in an institutional formulary appears to lend itself readily to quantitative techniques such as decision analysis and cost-benefit analysis, a review of the literature reveals that very little has been published in this area. Several of the published decision analyses use non-standard techniques that are, at best, of unproved validity, and may seriously distort the underlying issues through covert under-counting or double-counting of various drug attributes. Well executed decision analyses have contributed to establishing that drug acquisition costs are not an adequate measure of the total economic impact of formulary decisions and that costs of labour and materials associated with drug administration must be calculated on an institution-specific basis to reflect unique staffing patterns, bulk purchasing practices, and the availability of surplus capacity within the institution which might be mobilised at little marginal cost.

Decreased efficacy of inhaled pentamidine in the prevention of Pneumocystis carinii pneumonia among HIV-infected patients with severe immunodeficiency.

Study Objective: To determine the relationship between the degree of immune deficiency and the risk of Pneumocystis carinii pneumonia (PCP) among HIV-infected patients receiving inhaled pentamidine prophylaxis.

Design: Retrospective chart review.

Setting: AIDS clinic of inner-city hospital.

Influenza and pneumococcal vaccination of HIV-infected patients: a policy analysis.

Objective: To analyze the policy of vaccinating human immunodeficiency virus (HIV)-infected young adults against influenza and pneumococcal infections.

Methods: Transition state model of clinical immune deterioration of HIV infection, published data, and experts' estimates for the uncertain variables. Outcome measures are the number of influenza and pneumococcal infection hospitalizations and deaths prevented over 10 years and cost-effectiveness ratios.

Preventive medicine for HIV-infected patients: an analysis of isoniazid prophylaxis for tuberculin reactors and for anergic patients.

Objective: To analyze the policies of isoniazid prophylaxis for human immunodeficiency virus (HIV)-infected tuberculin reactors and for HIV-infected anergic patients with unknown tuberculin status.

Methods: Transition-state model of clinical immune deterioration of HIV-infection over ten years, review of published data, and a survey of AIDS experts. Outcome measures are the numbers of tuberculosis cases and deaths prevented and isoniazid toxicity cases and deaths occurring with prophylaxis.

Cost effectiveness of cervical cancer screening for the elderly.

Objective: To analyze the costs and benefits of alternative cervical cancer screening schedules among elderly women.

Setting: Population-based screening programs.

Design: A Markov model predicts the outcomes of periodic screening, diagnosis, and treatment for cervical cancer among women from 65 to 109 years of age.

Ambulatory blood pressure monitoring: is it cost-effective?

The detection and treatment of hypertension can prevent cerebrovascular disease and, to some extent, coronary heart disease. For mild hypertension this process is not efficient because many patients must be treated with antihypertensive medication to benefit only a few. The costs of identification, diagnosis and drug treatment of mild hypertension are significant.

Development of faculty consultants in a problem-based third year community medicine clerkship.

This paper describes the development of consultancy groups in behavioral science, epidemiology and biostatistics, and information science in a required community medicine rotation with a twenty year history. The addition of consultants to individual student tutors and field preceptors has led to a structure which promotes student-project flexibility, development of critical assessment skills and independent learning while maximizing faculty expertise and effectiveness.

Tuberculosis in house staff. A decision analysis comparing the tuberculin screening strategy with the BCG vaccination.

The BCG vaccination is not recommended for health-care workers in the United States. The current strategy against tuberculosis in tuberculin-negative house staff is an annual tuberculin screening test followed by chemoprophylaxis with isoniazid for a positive result. We performed a decision analysis that unequivocally concluded that the BCG vaccination leads to fewer cases of tuberculosis in this population over a 10-yr period.

Clinical implications of screening for cervical cancer under Medicare. The natural history of cervical cancer in the elderly: what do we know? What do we need to know?

Despite the recent passage of coverage for Papanicolaou test screening under Medicare, several aspects of the natural history of cervical cancer in the elderly remain uncertain. This article reviews what we know about cervical cancer in elderly women to provide clinicians with the background necessary for assessments of screening recommendations, integration of new data into practice, and development of consensus approaches to screening in the elderly. Two central questions that affect a screening program for the elderly are how long the neoplastic process takes from preinvasive disease to the development of invasive cancer, and how likely is it that a given neoplastic state observed in an elderly woman will, in fact, progress to a more severe state.

Sequential decision making with continuous disease states and measurements: II. Application to diastolic blood pressure.

The model and strategy for sequential decision making using normally distributed measurements proposed in a companion paper are applied to the problem of diagnosing diastolic hypertension. The assumptions of the model are discussed and justified clinically. Methods for assigning values to the model's parameters are explained and illustrated in the context of a hypothetical "generic" patient.

Sequential decision making with continuous disease states and measurements: I. Theory.

The question of whether to perform a continuous valued test to assess a continuous valued health state such as blood pressure or serum cholesterol is explored by decision analysis. Principal assumptions are that the underlying health state and measurement variability are both normally distributed, and that the impact of treatment on the utility of outcomes varies linearly with the underlying health state. Using Bayes' theorem, an expression for the expected utility of performing the test is derived and compared with immediate treatment or decision to withhold treatment.

Tuberculin screening: cost-effectiveness analysis of various testing schedules.

Because there is no tuberculin screening schedule currently recommended for adults, we used a Markov process in a cost-effectiveness analysis to determine an optimal strategy. We simulated the prognosis of a cohort of black 20-year-olds to evaluate the effects of various screening schedules with intradermal tuberculin and administration of isoniazid prophylaxis to those with positive results. The schedule with the lowest cost-effectiveness ratio is a single screening at 50 years of age, which costs $41,672 per quality-adjusted life year (QALY) gained.

Evaluating women's attitudes and perceptions in developing mammography promotion messages.

Breast cancer is a leading cause of cancer deaths in women. Although mammography is recognized as the most effective early detection method for breast cancer, it remains underutilized. Communications theory and practice, with its emphasis on formative research, can provide a basis for developing strategies effective in changing mammography-related behaviors.

Sequential analysis in a Bayesian model of diastolic blood pressure measurement.

A sequential method for diagnosing or excluding hypertension based on the Bayesian model of diastolic blood pressure presented in a companion article is presented. The likelihood ratio method of Wald is modified to include the effects of a prior probability distribution and to constrain the strategy to achieve specified positive and negative predictive values. The resulting formulas for upper and lower limits to diagnose and exclude diastolic hypertension can be evaluated using a hand calculator and a table of areas of the standard normal distribution.

Bayesian analysis of diastolic blood pressure measurement.

A mathematical model is presented for measurements that include substantial fluctuation and error. Under the assumptions that the fluctuation-error variance is the same for all subjects, and that the distributions of fluctuation-error variance within subjects and "true" values of the measurements in the population are normal, Bayes' theorem produces a simple estimate of the "true" value of a measurement, and a standard error, conditional on a single observation. The model is easily extended to several observations.

Tuberculosis prevention: cost-effectiveness analysis of isoniazid chemoprophylaxis.

Isoniazid chemoprophylaxis is not recommended for all persons infected with tubercle bacilli. Because of the small but significant risk of isoniazid hepatotoxicity, chemoprophylaxis is reserved for only those at the highest risk of tuberculosis activation. To evaluate this policy, we performed a cost-effectiveness analysis of isoniazid chemoprophylaxis for two populations with positive tuberculin skin tests: recent tuberculin converters, who are at high risk for activation, and older tuberculin reactors, who have a low risk for activation and for whom chemoprophylaxis is not now recommended.