Biomedical subjects

W B Bilker

Publications and source records attributed to W B Bilker.

At least 37 records · Page 2Linked to original sources

PubMed1999

An efficient design for verifying disease outcome status in large cohorts with rare exposures and low disease rates.

Cohort studies require the use of large samples when the risk of the event is very low. Databases that are large and population-based, such as Medicaid files, are frequently used for cohort studies, since they provide access to the large samples required for adequate statistical power at a relatively affordable cost. Epidemiologic studies using these databases typically require verification of reported diagnoses, however, because of the potential for errors in disease reporting. When exposure prevalence is also low, as in many pharmacoepidemiologic investigations of drug toxicity, there are few exposed cases compared to the number of unexposed cases. Verification of all unexposed presumptive cases through medical records is costly. We investigate the statistical efficiency of a design in which all exposed cases but only a subsample of the unexposed cases are verified. We show that good efficiency can usually be achieved with a small subsample of unexposed cases. Published in 1999 by John Wiley & Sons, Ltd.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1999

Gender effects on odor-stimulated functional magnetic resonance imaging.

On standardized tests of odor identification and odor detection, women tend to score better than men at nearly all age groups. We sought to determine if these findings would translate to differences between the sexes in the volume of activated brain when odors are presented to subjects as the stimulants for functional magnetic resonance imaging (FMRI) experiments. The activation maps of eight right-handed women (mean age 25.3 years old, range 20-44, S.D. 8.3 years) were compared with those of 8 right-handed men (mean age 30.5, range 18-37, S.D. 6.5 years) given the same olfactory nerve stimuli in an FMRI experiment at 1.5 T. Olfactory stimuli were delivered to the patients in a passive fashion using a Burghart OM4-B olfactometer with a nose piece inserted into the patients' nostrils. We used agents (eugenol, phenyl ethyl alcohol, or phenyl ethyl alcohol alternating with hydrogen sulfide) that were selective for olfactory nerve stimulation in the nose. The odorants were delivered to both nostrils for 1 s every 4 s during a 30 s 'on-period'. During the 30 s 'off-period', the patient received room air at the same flow rate. The women's group-averaged activation maps showed up to eight times more activated voxels than men for specific regions of the brain (frontal and perisylvian regions). The left and right inferior frontal regions showed a statistically significant increase in activation in women at p<0.01. In general, more women showed activation than men. The results suggest that (1) FMRI activation maps in subject groups can demonstrate correlates to psychophysical tests of olfaction, and (2) one must control for gender when performing odor-stimulated FMRI experiments.

Adolescent↗

PubMed1999

Factors influencing the optimal control-to-case ratio in matched case-control studies.

Statistical power in matched case-control studies depends on both the correlation coefficient between cases and their matched controls (phi) and the prevalence of exposure among controls (P0). To examine the hypothesis that the value of increasing the control-to-case ratio beyond 5 varies with both phi and P0, the authors estimated statistical power for a hypothetical case-control study under different assumptions. The effect of increasing the control-to-case ratio depended on phi and, to a lesser extent, on P0. The results suggest that investigators consider including more than five controls per case when either phi is greater than about 0.2 or P, is less than about 0.15.

Bias↗

PubMed1999

Reduced gray matter volume in schizophrenia.

BACKGROUND: There is emerging evidence that gray matter (GM) is reduced in patients with schizophrenia. Information on the extent of global differences in the 3 principal supertentorial compartments is necessary for interpretation of regional effects. The relation of GM reduction to clinical status and neurocognition also requires examination. METHODS: Magnetic resonance imaging, neurocognitive measures, and clinical assessment of symptoms and functioning were obtained for 130 patients (51 neuroleptic naive, 79 previously treated) and 130 healthy controls (75 men, 55 women in each group). RESULTS: Overall GM volume was reduced in patients compared with controls. This was evident in men (6% reduction) and women (2% reduction) and was already evident at the first presentation of neuroleptic-naive patients. The reduction sustained correction for age and total intracranial volume. Compartmental volumes did not correlate with the severity of positive (r, -0.08 to 0.23) or negative (r, -0.01 to -0.07) symptoms, but GM volume was associated with better premorbid functioning in women (r, 0.36-0.51). Small but significant correlations (r, 0.19-0.44) were observed between GM volume and performance in 6 neurocognitive domains. These correlations varied by diagnosis, most higher in patients, and were moderated by sex. CONCLUSIONS: Gray matter volume reduction in schizophrenia is already evident in men and women at first presentation. While this reduction is not correlated with symptom severity, it is associated with cognitive performance. Since GM development accelerates in the later part of gestation, while white matter growth is primarily postnatal, the results may support the hypothesis that neurodevelopmental processes relate to GM deficit.

Adult↗

PubMed1999

Association of dialyzer reuse with hospitalization and survival rates among U.S. hemodialysis patients: do comorbidities matter?

The objective of this study was to determine whether the associations between reuse of hemodialyzers and higher rates of death and hospitalization persist after adjustment for comorbidity. This was a nonconcurrent cohort study of survival and hospitalization rates among 1491 U.S. chronic hemodialysis patients beginning treatment in 1986 and 1987. The impact of dialyzer reuse was compared across three survival models: an unadjusted model, a "base" model adjusted only for demographics and renal diagnosis, and an "augmented" model additionally adjusted for comorbidities. We found that reuse of dialyzers was associated with a similarly higher rate of death in analyses unadjusted for confounders (relative risk [RR] 1.25, 95% confidence interval [CI] 0.97-1.61), adjusted for demographics and renal diagnosis (RR 1.16, 95% CI 0.96-1.41), and analyses additionally adjusted for comorbidities (RR = 1.25, CI, 1.03, 1.52). Reusing dialyzers was also associated with a greater rate of hospitalization that was stable regardless of adjustment procedures. We conclude that higher rates of death and hospitalization associated with dialyzer reuse persist regardless of adjustment for demographic characteristics or baseline comorbidities. These findings amplify concerns that there exists elevated morbidity among hemodialysis patients treated in facilities that reuse hemodialyzers. Although the association we observed was not confounded by comorbidity, a cause-and-effect relationship between dialyzer reuse and morbidity could not be proved because of the inability to control for aspects of care other than dialyzer reuse.

Adult↗

PubMed1999

Posttraumatic smell loss: relationship of psychophysical tests and volumes of the olfactory bulbs and tracts and the temporal lobes.

RATIONALE AND OBJECTIVES: The purpose of this study was to define the primary sites of injury in patients with posttraumatic anosmia and hyposmia with magnetic resonance (MR) imaging and to determine if these sites correlated with the results of psychophysical olfactory tests. MATERIALS AND METHODS: Thirty-six patients with subjective loss in olfaction after head trauma underwent volumetric MR studies of the olfactory bulbs and tracts and temporal lobes. Pearson correlations were computed between olfactory bulb and tract and temporal lobe volumes and the patients' scores on tests of odor identification (including the University of Pennsylvania Smell Identification Test [UPSIT]), detection, and memory. Analysis of variance was used to compare volumes of the control subjects and the posttraumatic patients. RESULTS: The olfactory bulbs and tracts (32 [89%] of 36 patients), the subfrontal lobes (22 [61%] of 36 patients), and the temporal lobes (11 [31%] of 36 patients) showed the highest incidence of posttraumatic encephalomalacia. Left olfactory bulb and tract volumes showed a statistically significant correlation with left and total UPSIT scores. A statistically significant difference (P < .001) was found in the right and left olfactory bulb and tract volumes between anosmic and hyposmic patients and between posttraumatic patients and control subjects. CONCLUSION: Olfactory bulb and tract damage may correlate with deficits in odor identification. Olfactory bulb and tract and frontal lobe encephalomalacia coexist in many patients.

Adolescent↗

PubMed1999

Primary care physicians' decisions to perform flexible sigmoidoscopy.

OBJECTIVE: This study was designed to identify factors that influence primary care physicians' willingness to perform flexible sigmoidoscopy. MEASUREMENTS: Using a mailed questionnaire, we surveyed all 161 primary care physicians participating in a large health care system. We obtained information on training, current practice patterns, beliefs about screening for colorectal cancer, and the influence of various factors on their decision whether or not to perform flexible sigmoidoscopy in practice. MAIN RESULTS: Of the 131 physicians included in the analysis, 68 (52%) reported training in flexible sigmoidoscopy, of whom 36 (53%) were currently performing flexible sigmoidoscopy in practice. Time required to perform flexible sigmoidoscopy, availability of adequately trained staff, and availability of flexible sigmoidoscopy services provided by other clinicians were identified most often as reasons not to perform the procedure in practice. Male physicians were more likely than female physicians to report either performing flexible sigmoidoscopy or desiring to train to perform flexible sigmoidoscopy (odds ratio 2.61; 95% confidence interval 1.10, 6.23). This observed difference appears to be mediated through different weighting of decision criteria by male and female physicians. CONCLUSIONS: Approximately half of these primary care physicians trained in flexible sigmoidoscopy chose not to perform this procedure in practice. Self-perceived inefficiency in performing office-based flexible sigmoidoscopy deterred many of these physicians from providing this service for their patients.

Adult↗

PubMed1999

Enterococcal bacteremia: risk factors for vancomycin resistance and predictors of mortality.

OBJECTIVE: To identify risk factors for vancomycin resistance and mortality in enterococcal bacteremia. DESIGN: Historical cohort study. SETTING: A large academic medical center with a high prevalence of vancomycin-resistant enterococci (VRE). PATIENTS: Two hundred sixty patients with enterococcal bacteremia, of whom 72 (28%) had VRE. RESULTS: Independent risk factors for infection with VRE were the mean number of antibiotic days (P<.001), renal insufficiency (P<.001), mean days of vancomycin use (P = .005), and neutropenia (P = .013). A trend toward a significant association between metronidazole use and VRE also was noted (P = .068). Mortality was attributable to the bacteremia in 96 patients (37%). Severity of illness (P<.001) and age (P = .020) were independent risk factors for mortality. Vancomycin resistance was not, however, an independent predictor of mortality. CONCLUSION: These results suggest that restrictions on antibiotic use, particularly in patients with renal insufficiency and neutropenia, may help to combat the rising incidence of VRE. Although patients with VRE bacteremia demonstrated higher mortality rates than patients with infection due to susceptible isolates, vancomycin resistance was not an independent predictor of mortality in these patients and likely serves more as a marker of underlying severity of illness.

Adolescent↗

PubMed1999

Association of dialyzer reuse and hospitalization rates among hemodialysis patients in the US.

OBJECTIVES: To determine if reuse of hemodialyzers is associated with higher rates of hospitalization and their resulting costs among end-stage renal disease (ESRD) patients. METHODS: Noncurrent cohort study of hospitalization rates among 27,264 ESRD patients beginning hemodialysis in the United States in 1986 and 1987. RESULTS: Dialysis in free-standing facilities reprocessing dialyzers was associated with a greater rate of hospitalization than in facilities not reprocessing (relative rate (RR) = 1.08, 95% confidence interval (CI), 1.02-1.14). This higher rate of hospitalization was observed with dialyzer reuse using peracetic/acetic acids (RR = 1.11, CI 1. 04-1.18) and formaldehyde (RR = 1.07, CI 1.00-1.14), but not glutaraldehyde (p = 0.97). There was no difference among hospitalization rates in hospital-based facilities reprocessing dialyzers with any sterilant and those not reprocessing. Hospitalization for causes other than vascular access morbidity in free-standing facilities reusing dialyzers with formaldehyde was not different from hospitalization in facilities not reusing. However, reuse with peracetic/acetic acids was associated with higher rates of hospitalization than formaldehyde (RR = 1.08, CI 1.03-1.15). CONCLUSIONS: Dialysis in free-standing facilities reprocessing dialyzers with peracetic/acetic acids or formaldehyde was associated with greater hospitalization than dialysis without dialyzer reprocessing. This greater hospitalization accounts for a large increment in inpatient stays in the USA. These findings raise important concerns about potentially avoidable morbidity among hemodialysis patients.

Cohort Studies↗

PubMed1998

Olfactory bulb and tract and temporal lobe volumes. Normative data across decades.

The sense of smell shows a diminution with age as measured by the University of Pennsylvania Smell Identification Test (UPSIT). To ascertain whether the volumes of the olfactory bulbs and tracts (OBTs) and the temporal lobes (TL) declined in parallel to smell function, we examined 36 individuals from ages 22 to 78 who did not complain of any loss of the sense of smell using magnetic resonance (MR) imaging. The OBT volumes showed an initial increase to the 4th decade of life and then a decrease with increasing age, while the trend in TL volume was not as dramatic. There was no correlation between OBT or TL volumes with unilateral or total UPSIT scores. The normative data by decades can be used to assess the OBTs of cohorts of patients with neurodegenerative disorders that affect olfaction.

Adult↗

PubMed1998

Identification of oncofetal fibronectin in patients with advanced epithelial ovarian cancer: detection in ascitic fluid and localization to primary sites and metastatic implants.

BACKGROUND: The mechanisms by which metastatic ovarian cancer adheres to peritoneal surfaces are not well understood. A role for tumor-derived extracellular matrix adhesive molecules such as fibronectin (FN) has been proposed. Because oncofetal fibronectin (onfFN) isoforms function in the adhesion of trophoblasts and have been identified in association with several malignancies, we sought to study onfFN in patients with advanced epithelial ovarian cancer. METHODS: Total FN was identified with the nonspecific anti-FN monoclonal antibody CAF. OnfFN was identified using the specific monoclonal antibodies FDC-6 and X18A4. These antibodies were applied to: 1) ascitic fluid from advanced epithelial ovarian cancer patients and peritoneal fluid from patients without pathologic conditions and 2) tissue sections of primary lesions and metastatic ovarian cancer implants. Comparative histologic specimens included normal ovarian tissue and small bowel implants of endometriosis. RESULTS: When measured by sandwich enzyme-linked immunoadsorbent assay, all peritoneal fluids (32 malignant and 32 benign) contained marked quantities of total (CAF reactive) FN, although malignant ascites had higher concentrations than benign samples (173.2 +/- 36.8 microg/mL vs. 76.4 +/- 31.8 microg/mL; P = 0.001). Malignant ascites also had significantly higher levels of onfFN than benign peritoneal fluid (FDC-6: 3.4 +/- 0.6 vs. 0.9 +/- 0.2 microg/mL; and X18A4: 5.1 +/- 1.3 vs. 1.1 +/- 0.4 microg/mL; P = 0.0001). Immunohistochemical staining of malignant lesions revealed prominent localization of both CAF reactive FN and onfFN to the stroma surrounding epithelial tumor nests. More delicate fibrillar staining within tumor nests also was evident. In contrast, implants of endometriosis revealed strong stromal staining for CAF reactive FN but not for onfFN. CONCLUSIONS: These results demonstrate the presence of onfFN in advanced ovarian malignancies. We speculate that onfFN may participate in tumor-associated peritoneal adhesive interactions.

Adenocarcinoma, Clear Cell↗

PubMed1998

The role of chloramphenicol in the treatment of bloodstream infection due to vancomycin-resistant Enterococcus.

The incidence of bacteremia due to vancomycin-resistant Enterococcus (VRE) has increased markedly in recent years. We investigated the role of chloramphenicol in its treatment. All cases of VRE bacteremia occurring at our facility during a 45-month period were analyzed. The response to chloramphenicol, its effect on mortality, and the incidence of adverse effects were assessed. Fifty-one patients (65.4%) received chloramphenicol. Among patients in whom a response could be assessed, 22 (61.1%) of 36 demonstrated a clinical response, while 34 (79.1%) of 43 showed a microbiological response. Forty-two patients (53.8%) died as a result of the bacteremia. Although the mortality rate was lower for patients treated with chloramphenicol, the difference was not significant (odds ratio = 0.72; 95% confidence interval, 0.28-1.85; P = .49), nor was there an association between earlier initiation of therapy and reduced mortality (P = .45). In cases with central line-related bacteremia, there was no difference in mortality among patients treated with chloramphenicol, line removal, or both (P = .36). Although 16 patients (31.4%) had adverse effects, none could be definitely attributed to chloramphenicol. Although chloramphenicol was well-tolerated, no significant effect of its use on mortality could be demonstrated.

Adolescent↗

PubMed1997

Use of physician services among family caregivers of elderly persons with dementia.

It is well known that there is an excess of physical and psychological health problems among family caregivers of elderly persons with Alzheimer's disease and other dementias. The objective of this study was to determine whether the higher level of morbidity translates into a higher level of medical care utilization. Data from a previously completed longitudinal study of caregivers for elderly persons with dementia were merged with data on physician visits obtained from the computerized records of the Quebec Health Insurance Board. Utilization of physician care (adjusted for age, sex, number of chronic diseases, and depression) was no higher for family caregivers of elderly patients with Alzheimer's disease and other dementias than for comparable family members of older persons without dementia. The annual cost of physician care was almost identical among caregivers and noncaregivers. However, the pattern of utilization for the two groups was somewhat different: there was a significantly higher frequency of physician utilization among caregivers for services billed by psychiatrists and internal medicine specialists. In multivariate analysis, physician utilization was significantly associated with having more than one chronic condition and with increased age. Future studies should focus on determining whether caregivers neglect their own health care needs as a result of the exigencies of the caregiving role.

Adult↗

PubMed1997

Reproducibility and reliability of volumetric measurements of olfactory eloquent structures.

RATIONALE AND OBJECTIVES: The authors assessed the reliability and reproducibility of volumetric measurements of olfactory bulbs and tracts (OBTs) and temporal lobes (TLs) with magnetic resonance (MR) imaging. METHODS: Repetitive MR imaging of two phantoms and OBTs and TLs of patients was performed. Regions of interest were manually drawn around the relevant structures, and their volumes were measured at workstations. Intra- and interobserver variability for the two readers were measured. Intraclass and Pearson correlation coefficients and mean percentage differences were calculated. RESULTS: The measured phantom volumes were within 1.9%-12% of the true volumes with a variability of < or = 5%. Intraclass and Pearson correlation coefficients were > or = 0.919 for measurements by a single reader and > or = 0.924 for measurements by different readers. The inter- and intraobserver variabilities were < or = 4.2% for TL and 11.3%-14.6% for OBTs. CONCLUSION: Volumetric measurements of the olfactory apparatus can be reliably and accurately reproduced from MR images.

Humans↗

PubMed1997

Short-term safety of live attenuated Japanese encephalitis vaccine (SA14-14-2): results of a randomized trial with 26,239 subjects.

The short-term safety of an effective and inexpensive new live attenuated Japanese encephalitis vaccine (SA14-14-2) was studied in a randomized trial, using block randomization. Of 26,239 children who were enrolled, half received the vaccine and half served as controls. Subjects were prospectively followed for 30 days for severe adverse events, such as encephalitis, meningitis, and "all-cause" hospitalization. No cases of encephalitis or meningitis occurred in either group. The upper 95% confidence limit for adverse events not occurring among subjects receiving their first dose was 4.1/10,000. Risk ratios and 95% confidence intervals for other adverse events were 0.70 (0.43-1.15) for all-cause hospitalization, 0.91 (0.37-2.22) for seizure, and 0.79 (0.56-1.11) for fever lasting > or = 3 days. These data attest to the short-term safety of the SA14-14-2 virus strain and the hamster kidney cell substrate.

Animals↗

PubMed1997

Adenoidal width and HIV factors.

PURPOSE: To determine the factors that correspond to adenoidal hypertrophy, often prominent in human immunodeficiency virus (HIV)-positive patients. METHODS: The sagittal T1-weighted MR images of 21 HIV-positive patients (age range, 25 to 50 years; mean, 37 years) and 21 healthy control subjects (age range, 24 to 55 years; mean, 35 years) were reviewed blindly and independently by two radiologists who measured the maximal dimension of the nasopharyngeal lymphoid tissue. Twenty-six additional HIV-positive patients were combined with the original 21 HIV-positive patients, and the hematologic studies of these 47 patients were compared with the adenoidal measurements to assess whether a relationship existed between nasopharyngeal prominence and hematocrit, white blood cell count, and CD4 count. RESULTS: Mean adenoidal width was 6.76 mm (SD, 5.82) in the HIV-positive population, but was only 3.36 mm (SD, 2.48) in the age-matched control group. Age and HIV status correlated with nasopharyngeal width measurements. No relationship between adenoidal width and hematocrit, CD4 count, or white blood cell count was evident. CONCLUSION: After correcting for age, we found that adenoidal lymphoid tissue is more abundant in HIV-positive persons than in control subjects. The hematologic ramifications of this finding remain uncertain.

Adenoids↗

PubMed1996

Effect of dialyzer reuse on survival of patients treated with hemodialysis.

OBJECTIVE: To evaluate the impact of dialyzer reuse on the survival of US hemodialysis patients. STUDY DESIGN AND PARTICIPANTS: Nonconcurrent cohort study of 27938 patients beginning hemodialysis in the United States in 1986 and 1987. MAIN OUTCOME MEASURE: Patient survival. RESULTS: Dialysis in freestanding facilities reprocessing dialyzers with the combination of peracetic and acetic acids was associated with greater mortality than treatment in facilities not reprocessing dialyzers (rate ratio [RR],1.10, 95% confidence interval [CI], 1.02-1.18; P=.02) In contrast, there was no significant difference between survival in freestanding facilities reprocessing dialyzers with either formaldehyde (RR,1.03, 95% CI, 0.96-1.10; P=.45) or glutaraldehyde (RR, 1.13, 95% CI, 0.95-1.35, P=.18) and survival in freestanding facilities not reprocessing dialyzers. Among freestanding facilities reprocessing dialyzers, use of peracetic/acetic acid was associated with a higher rate of death than use of formaldehyde (RR = 1.08, 95% CI, 1.01-1.14; P=.02). There was no statistical difference between survival in hospital-based facilities reprocessing dialyzers with either peracetic/acetic acid (RR=0.95, 95% CI, 0.85-1.06; P=.40), formaldehyde (RR=1.06, 95% CI, 0.98-1.15; P=.12), or glutaraldehyde (RR=1.09, 95% CI, 0.71-1.67; P=.70) and survival in hospital-based facilities not reprocessing dialyzers. In addition, choice of sterilant was not associated with a statistically significant difference in survival among hospital-based facilities reprocessing dialyzers. CONCLUSIONS: Dialysis in freestanding facilities reprocessing dialyzers with peracetic/acetic acid may be associated with worse survival than dialysis in free-standing facilities not reprocessing dialyzers or in those reprocessing with formaldehyde. We were unable to determine whether these relationships arose from greater comorbidity among patients treated in facilities using peracetic/acetic acid, poor quality of dialysis procedures in these facilities, or direct toxicity of peracetic/acetic acid. These findings raise important concerns about potentially avoidable mortality among US hemodialysis patients treated in dialysis facilities reprocessing hemodialyzers.

Adult↗

PubMed1996

Effectiveness of live-attenuated Japanese encephalitis vaccine (SA14-14-2): a case-control study.

BACKGROUND: Japanese encephalitis is a major cause of death and disability throughout Asia, including the Indian subcontinent. Although an effective vaccine for Japanese encephalitis is available, hundreds of millions of susceptible individuals remain unimmunised because of the vaccine's cost. In 1988, an inexpensive live-attenuated vaccine (SA14-14-2) was licensed in China. We have measured the effectiveness of this vaccine. METHODS: In a case-control study in rural Sichuan Province, China, the 56 cases consisted of children admitted to hospital with acute Japanese encephalitis, and were confirmed serologically. 1299 village-matched and age-matched controls were identified, and vaccination histories obtained from pre-existing written records. FINDINGS: The effectiveness of one dose was 80% (95% Cl 44 to 93%); that of two doses was 97.5% (86 to 99.6%). Controlling for multiple potential confounders did not alter these results. INTERPRETATION: We conclude that a regimen of two doses of live-attenuated Japanese encephalitis vaccine, administered 1 year apart, is effective in the prevention of clinically important disease. Subsequent study is needed to assure the safety of this vaccine.

Animals↗