Global sensitivity analysis and Bayesian parameter inference for solute transport in porous media colonized by biofilms.

The concept of dual flowing continuum is a promising approach for modeling solute transport in porous media that includes biofilm phases. The highly dispersed transit time distributions often generated by these media are taken into consideration by simply stipulating that advection-dispersion transport occurs through both the porous and the biofilm phases. Both phases are coupled but assigned with contrasting hydrodynamic properties. However, the dual flowing continuum suffers from intrinsic equifinality in the sense that the outlet solute concentration can be the result of several parameter sets of the two flowing phases. To assess the applicability of the dual flowing continuum, we investigate how the model behaves with respect to its parameters. For the purpose of this study, a Global Sensitivity Analysis (GSA) and a Statistical Calibration (SC) of model parameters are performed for two transport scenarios that differ by the strength of interaction between the flowing phases. The GSA is shown to be a valuable tool to understand how the complex system behaves. The results indicate that the rate of mass transfer between the two phases is a key parameter of the model behavior and influences the identifiability of the other parameters. For weak mass exchanges, the output concentration is mainly controlled by the velocity in the porous medium and by the porosity of both flowing phases. In the case of large mass exchanges, the kinetics of this exchange also controls the output concentration. The SC results show that transport with large mass exchange between the flowing phases is more likely affected by equifinality than transport with weak exchange. The SC also indicates that weakly sensitive parameters, such as the dispersion in each phase, can be accurately identified. Removing them from calibration procedures is not recommended because it might result in biased estimations of the highly sensitive parameters.

A prospective study of delirium and prolonged hospital stay. Exploratory study.

Using explicit criteria, delirium was diagnosed in 15% of a cohort of 133 hospitalized patients. Following each patient's discharge or death, the length of stay was compared with the diagnosis related group-predicted length of hospitalization. An analysis of stay variations disclosed that delirious patients exceeded their predicted stay by an average of 13 days, while nondelirious patients exceeded theirs by 3.3 days. The mean (+/- SD) length of hospitalization for patients with delirium was significantly longer than for their nondelirious counterparts (21.6 +/- 23.7 days vs 10.6 +/- 10.1 days, respectively). Hospitals treating high proportions of patients with delirium as a comorbidity to a principal somatic diagnosis should institute measures for the early detection of and appropriate intervention in patients with this condition. These steps may help reduce prolonged hospitalizations and minimize financial risk under the current diagnosis related group reimbursement system.

Occupational injury and illness in the United States. Estimates of costs, morbidity, and mortality.

OBJECTIVE: To estimate the annual incidence, the mortality and the direct and indirect costs associated with occupational injuries and illnesses in the United States in 1992. DESIGN: Aggregation and analysis of national and large regional data sets collected by the Bureau of Labor Statistics, the National Council on Compensation Insurance, the National Center for Health Statistics, the Health Care Financing Administration, and other governmental bureaus and private firms. METHODS: To assess incidence of and mortality from occupational injuries and illnesses, we reviewed data from national surveys and applied an attributable risk proportion method. To assess costs, we used the human capital method that decomposes costs into direct categories such as medical and insurance administration expenses as well as indirect categories such as lost earnings, lost home production, and lost fringe benefits. Some cost estimates were drawn from the literature while others were generated within this study. Total costs were calculated by multiplying average costs by the number of injuries and illnesses in each diagnostic category. RESULTS: Approximately 6500 job-related deaths from injury, 13.2 million nonfatal injuries, 60,300 deaths from disease, and 862,200 illnesses are estimated to occur annually in the civilian American workforce. The total direct ($65 billion) plus indirect ($106 billion) costs were estimated to be $171 billion. Injuries cost $145 billion and illnesses $26 billion. These estimates are likely to be low, because they ignore costs associated with pain and suffering as well as those of within-home care provided by family members, and because the numbers of occupational injuries and illnesses are likely to be undercounted. CONCLUSIONS: The costs of occupational injuries and illnesses are high, in sharp contrast to the limited public attention and societal resources devoted to their prevention and amelioration. Occupational injuries and illnesses are an insufficiently appreciated contributor to the total burden of health care costs in the United States.

Association between HIV infection and cervical neoplasia: implications for clinical care of women at risk for both conditions.

OBJECTIVE: Both AIDS and cervical neoplasia (CN) can result from sexual transmission of HIV infection and may affect similar groups of women. Available data on the association between AIDS and CN have practical implications for gynecological care. We review these data to provide an estimate of the magnitude of the association between CN and HIV infection. DESIGN: Twenty-one studies were reviewed, including reports and abstracts published from January 1986 to July 1990. Of these, five included a comparison group and had sufficient data for inclusion in the analysis. RESULTS: All five controlled studies reported a significant association between HIV infection and CN. One included women with both intraepithelial and invasive lesions; the other four considered women with intraepithelial lesions only. The summary odds ratio indicated that the odds of HIV-infected women having CN are 4.9 (95% confidence interval, 3.0-8.2) times that of HIV-negative women. CONCLUSIONS: Research is needed to clarify etiological relationships and the role of human papillomavirus in the causal pathway of the observed association. Meanwhile, available data are sufficient to encourage regular Papanicolaou's smear screening of HIV-infected women, and HIV testing and counseling of women with CN considered at risk for HIV infection.

Cost offset from a psychiatric consultation-liaison intervention with elderly hip fracture patients.

OBJECTIVE: The authors hypothesized that psychiatric liaison screening of elderly patients with hip fractures would shorten the average length of hospital stay and increase the proportion of patients who returned home after discharge. METHOD: The study was performed at Mount Sinai Medical Center in New York and Northwestern Memorial Hospital in Chicago. The subjects were 452 patients 65 years or older who were consecutively admitted for surgical repair of fractured hips. During a baseline year the patients received traditional referral for psychiatric consultation. During the experimental year all the patients at Mount Sinai and the patients on one Northwestern Unit were screened for psychiatric consultation. RESULTS: The patients who received psychiatric liaison screening had a higher consultation rate than those who received traditional consultation. The rates of DSM-III disorders in the experimental year were 56% at Mount Sinai and 60% at Northwestern. The mean length of stay was reduced from 20.7 to 18.5 days at Mount Sinai and from 15.5 to 13.8 days at Northwestern, resulting in reductions in hospital costs ($647/day) of $166,926 and $97,361, respectively. Fees generated from Medicare service delivery could have paid for the $20,000 psychiatric intervention cost at each site. There was no difference, however, between the two years in the discharge placement of patients. CONCLUSIONS: Admission psychiatric liaison screening of elderly patients with hip fractures results in early detection of psychiatric morbidity, better psychiatric care, earlier discharge, and substantial cost savings to the hospital.

Continuous labor support from labor attendant for primiparous women: a meta-analysis.

OBJECTIVE: To evaluate the available literature on the effects of continuous labor support among primiparous women. DATA SOURCES: We did a Medline search using the keywords "labor support," "doula," and "monitrice." Papers published in English from 1965 to May 1995 were eligible for this review. We also cross-checked all the references in the selected reports. METHODS OF STUDY SELECTION: We identified seven randomized clinical trials published during that period; four of these were eligible for our meta-analysis. DATA EXTRACTION AND SYNTHESIS: Meta-analysis of four studies conducted among young, low-income, primiparous women who gave birth on a busy labor floor in the absence of a companion suggested that continuous labor support by a labor attendant shortens the duration of labor by 2.8 hours (95% confidence interval [CI] 2.2-3.4), doubles spontaneous vaginal birth (relative risk [RR] 2.01, 95% CI 1.5-2.7) and halves the frequency of oxytocin use (RR 0.44, 95% CI 0.4-0.7), forceps use (RR 0.46, 95% CI 0.3-0.7), and cesarean delivery rate (RR 0.54, 95% CI 0.4-0.7). Women with labor support also reported higher satisfaction and a better postpartum course. CONCLUSION: Labor support may have important positive effects on obstetric outcomes among young, disadvantaged women. Further studies on benefit relative to cost are needed before a broad-scale program is advocated.

Tuberculosis prevention: cost-effectiveness analysis of isoniazid chemoprophylaxis.

Isoniazid chemoprophylaxis is not recommended for all persons infected with tubercle bacilli. Because of the small but significant risk of isoniazid hepatotoxicity, chemoprophylaxis is reserved for only those at the highest risk of tuberculosis activation. To evaluate this policy, we performed a cost-effectiveness analysis of isoniazid chemoprophylaxis for two populations with positive tuberculin skin tests: recent tuberculin converters, who are at high risk for activation, and older tuberculin reactors, who have a low risk for activation and for whom chemoprophylaxis is not now recommended. The cost-effectiveness ratios found were stable, despite wide variations in model assumptions and probability estimates. For high-risk tuberculin reactors, chemoprophylaxis resulted in net medical care monetary savings, extended life expectancy, and fewer fatal illnesses. For low-risk tuberculin reactors, chemoprophylaxis resulted in positive, but small, health effects. Because the cost to gain these positive effects were also small, the resulting cost-effectiveness ratios were reasonable and in the realm of accepted prevention strategies: $12,625 to gain one year of life and $35,011 to avert one death. These findings suggest that the current policy is too restrictive and that many in the large population of low-risk tuberculin reactors should be considered for isoniazid chemoprophylaxis.

Tuberculin screening: cost-effectiveness analysis of various testing schedules.

Because there is no tuberculin screening schedule currently recommended for adults, we used a Markov process in a cost-effectiveness analysis to determine an optimal strategy. We simulated the prognosis of a cohort of black 20-year-olds to evaluate the effects of various screening schedules with intradermal tuberculin and administration of isoniazid prophylaxis to those with positive results. The schedule with the lowest cost-effectiveness ratio is a single screening at 50 years of age, which costs $41,672 per quality-adjusted life year (QALY) gained. The cost-effectiveness ratio is nearly the same for all schedules involving a single screening between 30 and 70 years of age. Repeated screening strategies are less cost effective. Sensitivity analysis shows that the range of acceptable screening strategies changes significantly under alternate assumptions about the mortality from isoniazid hepatitis. However, screening at 50 years of age remains nearly optimal under the alternatives considered. Altering the values of other parameters generally produced only small changes. Tuberculin screening at 50 years of age should be added to primary care preventive practices because the strategy is as cost effective as standard health interventions and is robust to alternative assumptions. If further research confirms the base case assumptions about isoniazid toxicity, consideration should be given to increasing screening to every 10 years, which would produce a larger health benefit, albeit at substantially higher cost.

Physician response to the United Mine Workers' cost-sharing program: the other side of the coin.

The effect of cost sharing on health services utilization is analyzed from a new perspective, that is, its effects on physician response to cost sharing. A primary data set was constructed using medical records and billing files from a large multispecialty group practice during the three-year period surrounding the introduction of cost sharing to the United Mine Workers Health and Retirement Fund. This same group practice also served an equally large number of patients covered by United Steelworkers' health benefit plans, for which similar utilization data were available. The questions addressed in this interinsurer study are: (1) to what extent does a physician's treatment of medically similar cases vary, following a drop in patient visits as a result of cost sharing? and (2) what is the impact, if any, on costs of care for other patients in the practice (e.g., "spillover effects" such as cost shifting)? Answers to these kinds of questions are necessary to predict the effects of cost sharing on overall health care costs. A fixed-effects model of physician service use was applied to data on episodes of treatment for all patients in a private group practice. This shows that the introduction of cost sharing to some patients in a practice does, in fact, increase the treatment costs to other patients in the same practice who remain under stable insurance plans. The analysis demonstrates that when the economic effects of cost sharing on physician service use are analyzed for all patients within a physician practice, the findings are remarkably different from those of an analysis limited to those patients directly affected by cost sharing.

Results of the ACSUS for pediatric AIDS patients: utilization of services, functional status, and social severity.

OBJECTIVE: This study describes demographic characteristics of pediatric AIDS patients, describes hospital and community-based service utilization patterns, and analyzes medical and social support service usage patterns with respect to patient demographic characteristics, clinical trial participation, functional/developmental status, and social environment. DATA SOURCES AND STUDY SETTING: Data reported in this study are from the AIDS Costs and Service Utilization Survey (ACSUS) and cover the six-month period beginning March 1991 (N = 135). Pediatric patients who sought care for HIV-related problems were sampled at seven different hospitals in five metropolitan regions of the United States. All of the participating hospitals had clinics specifically serving pediatric patients infected with HIV. The sample consists of HIV-positive patients who had had at least one HIV-related symptom or condition. STUDY DESIGN: A stratified probability sample design guided the sampling strategy, which included oversampling in two large hospitals from two of the five metropolitan areas. Survey data cover an 18-month time period of health care utilization, cost, and financing information from HIV-infected patients and their providers. Utilization measures are standardized to a six-month period. Per capita income, family structure, informal personal network, functional status, and clinical trial participation are tested for associations with patterns of utilization. In addition, a weighted ten-point social severity scale was developed to assess family/household stability. DATA COLLECTION: Data were collected through a screener instrument completed by the person accompanying the child to a hospital clinic visit (usually a a parent), and through two interviews conducted in person with the patients' primary caregivers. Data from the questionnaires were coded and assembled into computerized SAS analysis files by WESTAT: PRINCIPAL FINDINGS: Children in this sample are 62 percent African American, 25 percent Hispanic, and 10 percent White. Medicaid is the primary payer for 92 percent. Mean per capita income is $3,440. Fewer than one-half (41 percent) of the families of the children receive Aid to Families with Dependent Children (AFDC). (AFDC). Within the six-month period, approximately one-third of the sample (29.6 percent) was hospitalized. Mean length of stay was 16.0 days. Clinical trial participation was positively related to mean number of hospital clinic visits and receipt of formal (paid) home care. There were no differences in use of community clinic, mental health, and inpatient facilities by clinical trial status. Participation in clinical trials was positively related to income and negatively related to social severity. In four cities, emergency room use was consistently lower for clinical trial participants than for nonparticipants. CONCLUSIONS: Data from the first six months of the ACSUS pediatric sample suggest that participation in clinical trials may bring about access to social services that appear to reduce emergency room use. However, the findings reported here are descriptive and exploratory. Further multivariate, nonparametric analyses of the full 18-month provider-patient merged data set are necessary to confirm the simple correlations found in this study.

Cost-effective policies for cervical cancer screening. An international review.

Screening programmes for cervical cancer have been credited with reducing the incidence of and mortality from cervical cancer. The main components of these screening programmes are: (i) their level of organisation; (ii) the age at which women begin screening; (iii) the age at which women discontinue screening; (iv) the interval between repeat screens; (v) the frequency at which the programmes provide screening; and (vi) the response to an abnormal screening test. However, not all screening programmes are equally efficient and differences in programme components can result in big differences in their cost effectiveness. Studies that employ cost-effectiveness analysis (CEA) to examine the efficiency of different programme components can inform the development of cost-effective programmes. This article presents findings of an international review of cost-effectiveness studies of cervical cancer screening. These studies consistently find that certain types of programmes are more cost effective than others. Programmes that are centrally organised and implemented by the public sector are reported to be more cost effective than those that use public funds for screening at other medical visits (convenience screening), or those that provide guidelines for healthcare professionals and the public to promote spontaneous discretionary screening. There is also substantial agreement about the cost effectiveness of other programme components. When multiple screenings are possible, studies report that they should generally begin at age 25 to 35 years and end at age 65 to 70 years, although it is important that older women have 3 normal Papanicolaou (Pap) smears before the discontinuation of screening. The interval for repeat screens that is reported to provide the best balance between cost and life-years saved is between 3 and 5 years. However, when a choice must be made between screening more women fewer times, or screening fewer women more times, most studies indicate that it is more cost effective to prioritize resources to obtain at least one screening for each woman. The screening of previously unscreened and high-risk populations has been shown to be especially cost effective. Despite this agreement, many studies report that models of the cost effectiveness of screening for cervical cancer are sensitive to a number of parameters. Changes in the attendance rate of the programme, the quality of the Pap smear, and the cost of the Pap smear can markedly change the cost effectiveness of a screening programme. Finally, this review discusses different perspectives of social choice analysis (e.g. CEA and cost-benefit analysis), when the objective is to prevent cervical cancer and the options are to screen, detect and treat, to reduce behavioural risk factors, and/or to pursue promising biological research.

The impact of laparoscopic surgery in the management of adnexal masses.

The objective of this study is to evaluate the clinical aspects of laparoscopic management of adnexal masses. The feasibility of this approach has been demonstrated, but the safe and effective use of laparoscopy for this indication requires training, technical skills and experience on the part of the laparoscopist. If used appropriately, many patients will benefit from minimally-invasive surgery. We compared clinical factors of patients having laparoscopy to those having laparotomy in a case-control study of 30 patients with adnexal masses. Oophorectomy or ovarian cystectomy was performed by laparoscopy for 20 women and by laparotomy for 10 women. Comparing the 2 groups, the most significant difference was the decrease in length of hospital stay in the laparoscopy group. There were no significant differences in operative time or intraoperative complications. Estimated blood loss was lower in the laparoscopy group, and no intraoperative complications occurred. No patient required conversion from laparoscopy to laparotomy. All patients had benign disease despite the inclusion of patients with risk factors for ovarian carcinoma. This study clearly demonstrates the clinical benefits of laparoscopic management of adnexal masses treated with oophorectomy or ovarian cystectomy.

Hospital care grievances and psychosocial needs expressed by PWAs: an analysis of qualitative data.

Despite the growing number of HIV-related hospital admissions, reports of hospitalization experiences of persons with AIDS has been sparse. As part of a larger quantitative study to assess how arrangements of care of patients with AIDS are related to quality of care, the authors analyzed qualitative data collected during interviews with 50 patients hospitalized for HIV-related complications. The responses are suggestive of problematic hospital care issues and indicate psychosocial concerns. Overarching themes emerged of communication deficits and depersonalizing behavior. This research can help healthcare professionals develop increased sensitivity to patients' perspectives of their circumstances. More extensive research is needed to evaluate and improve the experiences of patients during hospitalization for HIV-related illness.

Satisfaction with home healthcare services for clients with HIV: preliminary findings.

The Visiting Nurse Service of New York and Empire Blue Cross and Blue Shield implemented in 1990 the "At Home Options Program" (AHOP), an enhanced package of home care and other noninpatient services for HIV-positive clients. AHOP aims to reduce total treatment costs and hospital days. Clients (N = 52) completed mailed satisfaction surveys. Overall, clients were very satisfied with AHOP services. Clients expressed concerns, however, about the uneven quality of substitute paraprofessionals, and said they needed easier access to a knowledgeable healthcare professional. Operational concerns included inadequate information dissemination and administrative oversights. Findings will inform subsequent program activities.

A cost-effectiveness analysis of the high risk register and auditory brainstem response.

OBJECTIVE: To evaluate an infant hearing screening program utilizing the high risk register (HRR) and auditory brainstem response (ABR). DESIGN: A cost-effectiveness analysis of the screening program employing a retrospective cohort identified by chart review. The analysis was performed on a hypothetical cohort of 100,000 births and the results compared with a base model derived from literature review. SETTING: Mount Sinai Hospital, New York City, an urban, tertiary care institution. PATIENTS: All infants born between November 1990 and October 1993, approximately 16,500. Cost-effectiveness analysis focused on test results of 420 infants failing the HRR and 381 who subsequently received ABR. RESULTS: Analysis of the Mount Sinai Hospital (MSH) protocol showed it to be less cost-effective than other similar programs. The cost per hearing loss was far more at MSH than that found elsewhere. Further, the MSH program was ineffective in detecting infants with congenital hearing loss--identifying only one case between 1990 and 1993. Analysis of high risk criteria finds a low incidence of family history of hearing loss in the Mount Sinai cohort while other studies find a very high incidence. CONCLUSIONS: It appears that the poor performance of the MSH protocol is due to low specificity and sensitivity of the HRR. This generates a costly and ineffective program as follow-up exams focus on ruling-out false-positives rather than correctly identifying true hearing losses. Further evaluation is needed to determine whether changes in the application of the HRR or utilization of newer, low-cost tests such as otoacoustic emissions (OAE) may be effective in universal infant hearing screening.

The impact of housing status on health care utilization among persons with HIV disease.

This study sought to identify the prevalence of unstable housing situations, and for whom they occurred, and to examine differences in health care utilization by housing status. Housing status and inpatient and outpatient health care utilization of 1,851 HIV-infected individuals was ascertained through interviews. Nine percent of respondents were in unstable housing situations. Unstable housing was associated with significantly lower functional status. The unstably housed were more likely to visit an emergency room (p < 0.05) and had fewer ambulatory visits than persons with stable housing (p < 0.03). They incurred nearly five more hospital days and their average hospitalization was approximately 1.5 days longer than the stably housed, although these differences were not significant. Utilization of ambulatory care is lower among unstably housed persons with HIV disease, which may have led to their increased reliance upon emergency rooms and hospitals. Helping HIV-infected individuals maintain adequate housing could reverse this pattern.

Ambulatory blood pressure monitoring: is it cost-effective?

The detection and treatment of hypertension can prevent cerebrovascular disease and, to some extent, coronary heart disease. For mild hypertension this process is not efficient because many patients must be treated with antihypertensive medication to benefit only a few. The costs of identification, diagnosis and drug treatment of mild hypertension are significant. These costs have increased recently, in part due to changing patterns of drug selection favoring newer agents. Primary and secondary screening for hypertension has relied on casual blood pressure measurement which has high sensitivity, but low specificity, i.e. many false-positives can be expected. Incorporation of ambulatory blood pressure monitoring into secondary screening has potential for greater specificity by excluding from treatment 20-40% of those initially identified as having mild hypertension. Computer analysis of simulated populations selected for treatment by either casual blood pressure or by use of ambulatory blood pressure monitoring with echocardiography (for borderline cases) demonstrates no difference in calculated life expectancy for the two groups. However, the former strategy selected 23% of the subjects for treatment, while the latter selected 6%. These results imply that appropriate use of ambulatory blood pressure monitoring in secondary screening of mild hypertension may have a significant impact on cost-effectiveness.