Mean Failure Rates Research Articles

Predictors for failure of Pneumocystis carinii pneumonia prophylaxis. Multicenter AIDS Cohort Study

To identify clinical and epidemiological factors associated with failure of Pneumocystis carinii pneumonia (PCP) prophylaxis in those receiving primary and secondary prophylaxis. Longitudinal cohort study of participants infected with human immunodeficiency virus type 1 in the Multicenter AIDS Cohort Study who used PCP prophylaxis regimens after their T-helper lymphocyte counts had decreased to less than 0.200 x 10(9)/L (200/microL). Occurrence or recurrence of PCP. A total of 476 participants reported taking one or more of the following regimens: trimethoprim-sulfamethoxazole (TMP-SMX), dapsone, and/or aerosolized pentamidine--367 as primary prophylaxis and 109 as secondary prophylaxis after a previous episode of PCP. A total of 92 (20%) developed PCP despite prophylaxis. The mean failure rates per person-year of follow-up were 16.0% for those receiving primary prophylaxis and 12.1% for those receiving secondary prophylaxis (P = .19). Median times to death after initiation of primary or secondary prophylaxis were 2.0 and 1.2 years, respectively. The main predictor for failure of PCP prophylaxis was profound T-helper lymphocytopenia; 86% of failures occurred after T-helper cell counts decreased to less than 0.075 x 10(9)/L and 76% occurred after counts decreased to less than 0.050 x 10(9)/L. In multivariate time-dependent analysis, when compared with counts between 0.100 x 10(9)/L and 0.200 x 10(9)/L, the risk ratio for failure with counts less than 0.050 x 10(9)/L was 2.90 (P < .001). Once T-helper cell counts were considered, fever was the only other health status indicator that predicted subsequent PCP (ie, a time-dependent risk ratio of 2.22; P = .01). Use of TMP-SMX as the prophylaxis regimen was protective but did not eliminate failure (ie, a time-dependent risk ratio of 0.55; P = .03). These findings strongly support identifying improved methods of PCP prophylaxis once T-helper cell counts decrease to less than 0.075 x 10(9)/L or 0.100 x 10(9)/L. Given this severe degree of immunosuppression, an inherently more effective regimen against P carinii is required.

Predictors for Failure of Pneumocystis carinii Pneumonia Prophylaxis

Objective. —To identify clinical and epidemiological factors associated with failure of Pneumocystis carinii pneumonia (PCP) prophylaxis in those receiving primary and secondary prophylaxis. Design. —Longitudinal cohort study of participants infected with human immunodeficiency virus type 1 in the Multicenter AIDS Cohort Study who used PCP prophylaxis regimens after their T-helper lymphocyte counts had decreased to less than 0.200×10 9 /L (200/μL). Main Outcome Measure. —Occurrence or recurrence of PCP. Results. —A total of 476 participants reported taking one or more of the following regimens: trimethoprim-sulfamethoxazole (TMP-SMX), dapsone, and/or aerosolized pentamidine—367 as primary prophylaxis and 109 as secondary prophylaxis after a previous episode of PCP. A total of 92 (20%) developed PCP despite prophylaxis. The mean failure rates per person-year of follow-up were 16.0% for those receiving primary prophylaxis and 12.1% for those receiving secondary prophylaxis ( P =.19). Median times to death after initiation of primary or secondary prophylaxis were 2.0 and 1.2 years, respectively. The main predictor for failure of PCP prophylaxis was profound T-helper lymphocytopenia; 86% of failures occurred after T-helper cell counts decreased to less than 0.075×10 9 /L and 76% occurred after counts decreased to less than 0.050×10 9 /L. In multivariate time-dependent analysis, when compared with counts between 0.100×10 9 /L and 0.200×100 9 /L, the risk ratio for failure with counts less than 0.050×10 9 /L was 2.90 ( P P =.01). Use of TMP-SMX as the prophylaxis regimen was protective but did not eliminate failure (ie, a time-dependent risk ratio of 0.55; P =.03). Conclusions. —These findings strongly support identifying improved methods of PCP prophylaxis once T-helper cell counts decrease to less than 0.075×10 9 /L or 0.100×10 9 /L. Given this severe degree of immunosuppression, an inherently more effective regimen against P carinii is required. ( JAMA . 1995;273:1197-1202)

Logistic Simulation - A Credible Tool for Decision Makers?

Logistic simulation and sensitivity analyses can prove useful in management reviews of major weapon system acquistion programs. The F/A-18 analyses were instrumental in quantifying the importance of achieving projected field reliability levels, the adequacy of supply support funding, and the importance of test equipment capacity in achieving aircraft readiness objectives. Logistic simulation inputs and assumptions need to be subjected to critical examination in each application. In the case reviewed, it was found that the commonly used assumption that mean failure rates are constant values, known with certainty, introduced significant errors in prediction of operational readiness and sensitivity analysis results. The variability of mean demand has potentially far reaching implications concerning future support planning but further work is required to fully understand, characterize, model, and develop logistic support approaches that accommodate the variability. Logistic simulation has the potential to become an accepted support planning and analysis tool that will meet the new DoD management demands to quantitatively link system design and support decisions to operational readiness objectives. Further understanding of the ``real world,'' and incorporation of this understanding in input data and modeling techniques are required if the full potential of this support planning tool is to be realized.

Anchorage dependence: Correlation between amount of growth and diameter of bead, for single cells grown on individual glass beads

Single cells are attached to small glass beads and placed on a soft agar surface, over feeder cells. Experiments with BHK C13 cells on beads ranging from 20 to 60 μm in diameter suggest the existence of a threshold for cell growth at 50 μm. Cells on beads of larger diameter tend toward multilayers and smaller beads progressively fail to support growth. Mean failure rates for growth of cells ranged from 5% on 55 μm beads to 52% on 25 μm beads.