Browsing by Author "Kong, Nan"

Now showing 1 - 4 of 4
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    Cost Effectiveness of Different Strategies for Detecting Cirrhosis in Patients With Non-alcoholic Fatty Liver Disease Based on United States Health Care System
    (Elsevier, 2020) Vilar-Gomez, Eduardo; Lou, Zhouyang; Kong, Nan; Vuppalanchi, Raj; Imperiale, Thomas F.; Chalasani, Naga; Medicine, School of Medicine
    Background & Aims Several strategies are available for detecting cirrhosis in patients with non-alcoholic fatty liver disease (NAFLD), but their cost effectiveness is not clear. We developed a decision model to quantify the accuracy and costs of 9 single or combination strategies, including 3 noninvasive tests (fibrosis-4 [FIB-4], vibration controlled transient elastography [VCTE], and magnetic resonance elastography [MRE]) and liver biopsy, for detection of cirrhosis in patients with NAFLD. Methods Data on diagnostic accuracy, costs, adverse events, and cirrhosis outcomes over a 5-y period were obtained from publications. The diagnostic accuracy, per-patient cost per correct diagnosis of cirrhosis, and incremental cost-effectiveness ratios (ICER) were calculated for each strategy for base cirrhosis prevalence values of 0.27%, 2%, and 4%. Results The combination of the FIB-4 and VCTE identified patients with cirrhosis in NAFLD populations with a 0.27%, 2%, and 4% prevalence of cirrhosis with the lowest cost per person ($401, $690, and $1024, respectively) and highest diagnostic accuracy (89.3%, 88.5%, and 87.5% respectively). The combination of FIB-4 and MRE ranked second in cost per person ($491, $781, and $1114, respectively) and diagnostic accuracy (92.4%, 91.6%, 90.6%, respectively). Compared to the combination of FIB-4 and VCTE (least costly), the ICERs were lower for the combination of FIB-4 and MRE ($2864, $2918, and $2921) than the combination of FIB-4 and liver biopsy ($4454, $5156, and $5956) at the cirrhosis prevalence values tested. When goal was to avoid liver biopsy, FIB-4+VCTE and FIB-4+MRE had similar diagnostic accuracies, ranging from 87.5% to 89.3% and 90.6% to 92.4% for cirrhosis diagnosis, although FIB-4+MRE had a slightly higher cost. Conclusions In our cost effectiveness analysis based on United States health care system, we found that results from FIB-4, followed by either VCTE, MRE, or liver biopsy, detect cirrhosis in patients with NAFLD with a high level of accuracy and low cost. Compared to FIB-4 + VCTE which was the least costly strategy, FIB-4+MRE had lower ICER than FIB-4+LB.
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    Estimating age-dependent per-encounter chlamydia trachomatis acquisition risk via a Markov-based state-transition model
    (BioMed Central, 2014-04-25) Teng, Yu; Kong, Nan; Tu, Wanzhu; Biostatistics and Health Data Science, Richard M. Fairbanks School of Public Health
    Background: Chlamydial infection is a common bacterial sexually transmitted infection worldwide, caused by C. trachomatis. The screening for C. trachomatis has been proven to be successful. However, such success is not fully realized through tailoring the recommended screening strategies for different age groups. This is partly due to the knowledge gap in understanding how the infection is correlated with age. In this paper, we estimate age-dependent risks of acquiring C. trachomatis by adolescent women via unprotected heterosexual acts. Methods: We develop a time-varying Markov state-transition model and compute the incidences of chlamydial infection at discrete age points by simulating the state-transition model with candidate per-encounter acquisition risks and sampled numbers of unit-time unprotected coital events at different age points. We solve an optimization problem to identify the age-dependent estimates that offer the closest matches to the observed infection incidences. We also investigate the impact of antimicrobial treatment effectiveness on the parameter estimates and the differences between the acquisition risks for the first-time infections and repeated infections. Results: Our case study supports the beliefs that age is an inverse predictor of C. trachomatis transmission and that protective immunity developed after initial infection is only partial. Conclusions: Our modeling method offers a flexible and expandable platform for investigating STI transmission.
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    Optimizing strategies for population-based chlamydia infection screening among young women: an age-structured system dynamics approach
    (Springer (Biomed Central Ltd.), 2015) Teng, Yu; Kong, Nan; Tu, Wanzhu; Department of Biostatistics, School of Public Health
    BACKGROUND: Chlamydia infection (CT) is one of the most commonly reported sexually transmitted diseases. It is often referred to as a "silent" disease with the majority of infected people having no symptoms. Without early detection, it can progress to serious reproductive and other health problems. Economical identification of asymptomatically infected is a key public health challenge. Increasing evidence suggests that CT infection risk varies over the range of adolescence. Hence, age-dependent screening strategies with more frequent testing for certain age groups of higher risk may be cost-saving in controlling the disease. METHODS: We study the optimization of age-dependent screening strategies for population-based chlamydia infection screening among young women. We develop an age-structured compartment model for CT natural progress, screening, and treatment. We apply parameter optimization on the resultant PDE-based system dynamical models with the objective of minimizing the total care spending, including screening and treatment costs during the program period and anticipated costs of treating the sequelae afterwards). For ease of practical implementation, we also search for the best screening initiation age for strategies with a constant screening frequency. RESULTS: The optimal age-dependent strategies identified outperform the current CDC recommendations both in terms of total care spending and disease prevalence at the termination of the program. For example, the age-dependent strategy that allows monthly screening rate changes can save about 5% of the total spending. Our results suggest early initiation of CT screening is likely beneficial to the cost saving and prevalence reduction. Finally, our results imply that the strategy design may not be sensitive to accurate quantification of the age-specific CT infection risk if screening initiation age and screening rate are the only decisions to make. CONCLUSIONS: Our research demonstrates the potential economic benefit of age-dependent screening strategy design for population-based screening programs. It also showcases the applicability of age-structured system dynamical modeling to infectious disease control with increasing evidence on the age differences in infection risk. The research can be further improved with consideration of the difference between first-time infection and reinfection, as well as population heterogeneity in sexual partnership.
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    Second-look endoscopy for bleeding peptic ulcer disease: a decision-effectiveness and cost-effectiveness analysis
    (Wolters Kluwer, 2012) Imperiale, Thomas F.; Kong, Nan; Medicine, School of Medicine
    Background: Second-look endoscopy after initial therapeutic endoscopy for bleeding peptic ulcer disease may decrease the risk of rebleeding; however, it is not recommended routinely. Understanding conditions under which second-look endoscopy is beneficial might be useful for clinical decision making. Methods: Using a decision model, literature-based probabilities, and Medicare reimbursement costs, we compared routine second-look endoscopy with no second-look endoscopy. We measured rebleeding, need for surgery, hospital mortality, and costs, and calculated the cost to avoid each outcome, expressed as the number needed to treat, along with the cost per outcome prevented. Results: In the base case, routine second-look endoscopy reduced rebleeding from 16% to 10% (needed to treat=16) but had no effect on other outcomes. The cost to prevent 1 case of rebleeding was nearly $13,000. Threshold analysis revealed a rebleeding threshold of 31% to neutralize the cost difference between routine second-look endoscopy and no routine second-look endoscopy. If routine second-look endoscopy was 100% effective in preventing rebleeding, then the rebleeding threshold for cost neutrality would be 17.5%. When rebleeding risks after the index endoscopy and second-look endoscopy were simultaneously considered, the cost per bleed prevented ranged from a cost savings of $165 when the respective risks were 25% and 5%, to a cost of nearly $33,000 when the risks were 20% and 15%. Conclusions: The results suggest that routine second-look endoscopy is not indicated after therapeutic endoscopy for bleeding peptic ulcer disease. However, if rebleeding risk is 31% or greater, then routine second-look endoscopy reduces this risk at no additional cost.