Biomedical subjects

Haitao Chu

Publications and source records attributed to Haitao Chu.

22 records · Page 2Linked to original sources

PubMed2004

Estimating heterogeneous transmission with multiple infectives using MCMC methods.

We developed a general procedure for estimating the transmission probability adjusting for covariates when susceptibles are exposed to several infectives concurrently and taking correlation within transmission units into account. The procedure is motivated by a study estimating efficacy of pertussis vaccination based on the secondary attack rate in a rural sub-Saharan community (Niakhar, Senegal) and illustrated with simulations. The procedure is also appropriate to estimate the pairwise transmission probability in transmission studies of live vaccine virus in a collection of transmission units, such as day-care centres or retirement centres. Previously, analyses either excluded transmission units with multiple infectives or ignored co-infectives. Excluding transmission units with multiple infectives is statistically less efficient and ignoring co-infectives can lead to biased estimation. Modelling is carried out by regressing the latent pairwise transmission probability from each infective to a susceptible on covariates and specifying a transmission linkage function linking the latent pairwise transmission probability to the overall transmission probability. Parameters are estimated using Markov chain Monte Carlo methods.

Bayes Theorem↗

PubMed2004

Bayesian estimation of vaccine efficacy.

Protective vaccine efficacy, VEs, is measured as one minus the incidence rate ratio (IRR) or the relative risk (RR) in the vaccinated group compared with the unvaccinated group. In this paper, we systematically present Bayesian estimation of protective vaccine efficacy based on the Poisson and binomial distributions. We also propose a new tool, the vaccine efficacy acceptability curve, to represent the uncertainty for the estimate of the vaccine efficacy graphically. It is very useful, especially when there is no universal agreement on the acceptable vaccine efficacy. The vaccine efficacy acceptability curve is defined as the posterior probability that the measure of vaccine efficacy VEs > or = k for each acceptable value k. When a vaccine is highly efficacious, the number of vaccinated susceptibles being infected is likely to be very small or even zero. Then the assumptions of normality and log-normality of IRR or RR usually do not hold well. Although frequentist exact methods provide good estimates of the confidence interval, they are overly conservative and are computationally difficult to extend to estimate the vaccine efficacy acceptability curve. In this paper, our focus is on Bayesian estimation of protective vaccine efficacy, its highest probability density credible set, and the vaccine efficacy acceptability curve through Markov chain Monte Carlo (MCMC) methods. We illustrate the methods using the data from two pertussis vaccine studies and the H. influenza Type B preventive trial.

Bayes Theorem↗

PubMed2003

Estimating efficacy of trivalent, cold-adapted, influenza virus vaccine (CAIV-T) against influenza A (H1N1) and B using surveillance cultures.

The authors report on a community-based, nonrandomized, open-label study, conducted during the 2000-2001 influenza season in Temple-Belton, Texas, of the protective effectiveness of trivalent, cold-adapted, influenza virus vaccine (CAIV-T) in children aged 18 months-18 years. The dominant circulating strains in 2000-2001 were influenza A/New Caledonia/20/99 (H1N1) and influenza B/Sichuan/379/99. Children had access to CAIV-T during the 1998-1999, 1999-2000, and 2000-2001 influenza seasons. The vaccine included influenza A/Sydney/5/97 (H3N2) and B/Beijing/184/93-like (B/Ann Arbor/l/94) strains in all three seasons. The vaccine included A/Beijing/262/95 (H1N1) in 1998-1999 and 1999-2000, which was replaced by A/New Caledonia/20/99 (H1N1) in 2000-2001. When medically attended acute respiratory illness (MAARI) was used as the outcome, the protective effectiveness for children vaccinated in 2000 was 18% (95% confidence interval (CI): 11, 25). Based on a combination of a validation sample of surveillance cultures and the MAARI outcome, protective efficacy against combined influenza A (H1N1) and B was 79% (95% CI: 51, 91). The efficacy estimate, after accounting for missing influenza culture status, against influenza A (H1N1) alone was 92% (95% CI: 42, 99) and against a new variant of influenza B alone was 66% (95% CI: 9, 87). CAIV-T provides substantial protection against a mixture of influenza A (H1N1) and B. Results demonstrate the powerful potential of using validation sets for outcomes in vaccine field studies.

Adolescent↗

PubMed2002

Cost and cost-effectiveness of an early invasive vs conservative strategy for the treatment of unstable angina and non-ST-segment elevation myocardial infarction.

CONTEXT: In the Treat Angina with Aggrastat and Determine Cost of Therapy with an Invasive or Conservative Strategy (TACTICS)-Thrombolysis in Myocardial Infarction (TIMI) 18 trial, patients with either unstable angina or non-ST-segment elevation myocardial infarction (UA/NSTEMI) treated with the platelet glycoprotein (Gp IIb/IIIa) inhibitor tirofiban had a significantly reduced rate of major cardiac events at 6 months with an early invasive vs a conservative strategy. OBJECTIVE: To examine total 6-month costs and long-term cost-effectiveness of an invasive vs a conservative strategy. DESIGN: Randomized controlled trial including a priori economic end points. SETTING: Hospitalization for UA/NSTEMI with 6-month follow-up period. PATIENTS: A total of 2220 patients with UA/NSTEMI; economic data from 1722 patients at US-non-VA hospitals. INTERVENTION: Early invasive strategy with routine catheterization and revascularization as appropriate vs a conservative strategy with catheterization performed only for recurrent ischemia or a positive stress test. MAIN OUTCOME MEASURE: Total 6-month costs and incremental cost-effectiveness ratio. RESULTS: The average initial hospitalization costs among those in the invasive strategy group were $15714 vs $14047 among those in the conservative strategy group, a difference of $1667 (95% confidence interval [CI], $387-3091). The in-hospital costs were offset significantly at the 6-month follow-up, with an average cost in the invasive group of $6098 vs $7180 in the conservative group, a difference of $1082 (95% CI, -$2051 to $76). The average total costs at 6 months, including productivity costs, for the invasive group was $21 813 vs $21 227 for the conservative group, a $586 difference (95% CI, -$1087 to $2486). The average 6-month costs excluding productivity costs in the invasive group was $19 780 vs $19 111 in the conservative group, a difference of $670, 95% CI; (-$1035 to $2321). Estimated cost per year of life gained for the invasive strategy, based on projected life expectancy, was $12739 for the base case, and ranged from $8371 to $25769, based on model assumptions. CONCLUSIONS: In patients with UA/NSTEMI treated with the Gp IIb/IIIa inhibitor tirofiban, the clinical benefit of an early invasive strategy was achieved with a small increase in cost, yielding favorable projected estimates of cost per year of life gained. These results support the broader use of an early invasive strategy in these patients.

Aged↗