Estimates Of Infection Prevalence Research Articles

Cellular responses and disease expression in oysters ( Crassostrea virginica) exposed to suspended field — contaminated sediments

Exposure of oysters to water soluble fractions derived from field-contaminated sediments (FCS) containing predominantly lower molecular weight organic aromatic compounds, has been previously demonstrated to enhance pre-existing infections caused by the protozoan parasite, Perkinsus marinus (Dermo), and the prevalence of experimentally induced infections. To further explore the role of pollution on the onset and progression of disease, effects of suspended FCS from an estuarine creek in Virginia, USA, dominated by higher molecular weight polycyclic aromatic hydrocarbons (PAHs) on cellular responses and Dermo disease expression in oysters ( Crassostrea virginica) were examined. Sediments were collected from a PAH polluted estuarine creek in Virginia, USA. To test effects on cellular response, oysters from Maine were exposed daily to 0, 1.0, 1.5, or 2.0 g suspended FCS (corresponding to 0, 70.2, 105, or 140 μg PAHs, respectively) for 5, 10, 20, and 40 days. Hemocyte activities and plasma lipid, protein and lactate dehydrogenase (LDH) levels were then measured. Exposure stimulated neutral red uptake, MTT reduction, and 3H-leucine incorporation in oyster hemocytes at various exposure times, but did not affect the plasma protein, lipid and LDH levels. To test effects on Dermo expression, oysters from a Dermo enzootic area, with an initial estimated infection prevalence of 39%, were exposed daily to 0, 1.0, 1.5, or 2.0 g suspended FCS (corresponding to 0, 75.0, 113, or 150 μg PAHs, respectively) for 30 days. Exposure enhanced disease expression in oysters. However, no significant change was noted in any measured cellular or humoral parameters.

Logistic discrimination of mixtures of M. tuberculosis and non-specific tuberculin reactions.

Interpretation of the Mantoux test for tuberculous infection can be complicated by cross-reactions caused by infection with non-specific mycobacteria. Thus, the distribution of positive indurations is a mixture of two distributions. To estimate tuberculous infection prevalence, the marginal distribution of indurations needs to be separated into its component distributions. Observations from several populations with different mixes of the two types of infection are required. Homogeneity across populations of distributions of indurations for each type of infection is assumed. A logistic model is specified for the probability of having tuberculous infection conditional on the observed induration size. No other assumptions about the two distributions are made. Maximum likelihood is used to estimate the logistic function. Goodness-of-fit criteria are discussed. The method is applied to a series of tuberculin surveys carried out in (South) Korea. Estimated infection prevalence agrees reasonably well with several ad hoc criteria. The goodness-of-fit test rejects underlying assumptions of homogeneity. One reason appears to be a decline over time in induration sizes caused by tuberculous infection. However, not all reasons for this rejection are obvious. The proposed method of mixture analysis provides an additional tool for the interpretation of prevalence survey data where the diagnostic test lacks specificity as a result of cross-reactions.

Methodological issues in the estimation of the tuberculosis problem from tuberculin surveys

Setting: National tuberculin skin test surveys. Objectives: To review the operating characteristics of the tuberculin skin test, to ascertain the validity of estimating prevalence and risk of infection from tuberculin skin test surveys under various conditions, and to review constraints in the estimation of the magnitude of the tuberculosis problem in the community from such surveys. Methods: This report utilizes hypothetical and selected real data obtained in regional and national surveys at various points in time to exemplify methodological issues. Results: Risk of infection, the essence to be abstracted from tuberculin skin test surveys, theoretically allows for a comparison of the extent of transmission of tubercle bacilli in various populations. However, the conduct of tuberculin skin test surveys and the analysis and interpretation of their results are not free from important technical problems. Accurate estimation of infection prevalence is particularly vulnerable to the great variability of the test's specificity under various circumstances. Furthermore, the annual risk of infection has averaging characteristics that preclude a rapid assessment of changes in transmission patterns. Finally, estimates of infection risk do not necessarily provide a standardized parameter to derive incidence of infectious cases, because of variations in the quality of intervention and varying risks of progression from latent infection to overt tuberculosis. Conclusions: While tuberculin skin test surveys provide the currently most widely used means of assessing tuberculosis transmission patterns over prolonged periods of time in a community, results from such surveys must be interpreted with caution when accurate estimates of the tuberculosis problem are sought.