Profiling advanced disease in an Asian clinical human immunodeficiency virus cohort: comparison of two definitions for acquired immunodeficiency syndrome.

OBJECTIVE: To compare advanced human immunodeficiency virus disease defined immunologically and clinically by evaluating the characteristics of human immunodeficiency virus patients in Hong Kong. DESIGN: Retrospective observational study. SETTING: A human immunodeficiency virus cohort database established at a university and the major human immunodeficiency virus specialist services in Hong Kong. PATIENTS: Patients diagnosed with acquired immunodeficiency syndrome at the study centres between 1985 and 2006 were included. MAIN OUTCOME MEASURES: Comparison of advanced human immunodeficiency virus disease defined (a) clinically as World Health Organization stage IV, and (b) immunologically as a CD4 count lower than 350/microL. RESULTS: Between 1985 and 2006, a total of 1317 patients, a majority of whom Chinese, were evaluated. Of these, 914 (69%) and 335 (25%) fulfilled the criteria for immunologically and clinically defined advanced disease, respectively. The mean age of the study population was 38 years and male-to-female ratio 4:1. There were two peaks in the frequency distribution of CD4 counts, one at a low count of less than 100/microL and the other between 200 and 400/microL. All except four with clinically defined advanced disease had CD4 counts lower than 350/microL on presentation. Of those with immunologically defined advanced disease, men having sex with men accounted for a lower proportion in the clinically advanced category, and Pneumocystis pneumonia was the commonest advanced disease at presentation. CONCLUSIONS: Both clinical and immunological definitions provide a consistent means for assessing advanced disease, the implications of which are different. Such profiling has been made possible through the operation of a standardised cohort database, which is useful in (1) enhancing human immunodeficiency virus epidemiology studies, and (2) evaluating the performance of public health services.

Fluid shear influences on the performance of hydraulic flocculation systems.

Gravity driven hydraulic flocculators that operate in the absence of reliable electric power are better suited to meet the water treatment needs of green communities, resource-poor communities, and developing countries than conventional mechanical flocculators. However, current understanding regarding the proper design and operation of hydraulic flocculation systems is insufficient. Of particular interest is the optimal fluid shear level needed to produce low turbidity water. A hydraulic tube flocculator was used to study how fluid shear levels affect the settling properties of a flocculated alum-kaolin suspension. A Flocculation Residual Turbidity Analyzer (FReTA) was used to quantitatively compare the sedimentation velocity distributions and the post-sedimentation residual turbidities of the flocculated suspensions to see how they were affected by varying fluid shear, G, and hydraulic residence time, θ, while holding collision potential, Gθ, constant. Results show that floc breakup occurred at all velocity gradients evaluated. High floc settling velocities were correlated with low residual turbidities, both of which were optimized at low fluid shear levels and long fluid residence times. This study shows that, for hydraulic flocculation systems under the conditions described in this paper, low turbidity water is produced when fluid shear is kept at a minimum. Use of the product Gθ for design of laminar flow tube flocculators is insufficient if residual turbidity is used as the metric for performance. At any Gθ within the range tested in this study, best performance is obtained when G is small and θ is long.

Method for quantitative analysis of flocculation performance.

The sedimentation rate and the post-sedimentation residual turbidity of flocculated suspensions are properties central to the design and operation of unit processes following flocculation in a water treatment plant. A method for comparing flocculation performance based on these two properties is described. The flocculation residual turbidity analyzer (FReTA) records the turbidity of flocculent suspensions undergoing quiescent settling. The fixed distance across which flocs must travel to clear the measurement volume allows sedimentation velocity distributions of the flocculent suspension to be calculated from the raw turbidity data. By fitting the transformed turbidity data with a modified gamma distribution, the mean and variance of sedimentation velocity can be obtained along with the residual turbidity after a period of settling. This new analysis method can be used to quantitatively compare how differences in flocculator operating conditions affect the sedimentation velocity distribution of flocs as well as the post-sedimentation residual turbidity.