Powered, air-purifying particulate respirator filter penetration by a DOP aerosol

In 1995, new certification requirements for all nonpowered, air-purifying particulate filter respirators were put in place when 42 CFR 84 replaced 30 CFR 11. However, the certification requirements for all other classes of respirators, including powered air-purifying respirators (PAPRs), were transferred to 42 CFR 84 from 30 CFR 11 without major changes. Since the inception of 42 CFR 84, researchers have learned that the efficiency of electrostatic filter media, in contrast with mechanical filter media, can be rapidly degraded by oil aerosols. Further, confusion may exist among respirator users, since electrostatic PAPR filters have the same magenta color assigned to high-efficiency filters for nonpowered particulate respirators that have been tested and certified for use against oil aerosols (i.e., P100 filters). Users may expect that the magenta color of certified PAPR filters indicates suitability for use against oil aerosols. This may not be the case. To illustrate the potential degradation of electrostatic PAPR filters, new filters certified under 42 CFR 84 were tested using a TSI model 8122 Automated Respirator Tester against charged and neutralized DOP aerosols with intermittent loading schedules. The performance of a magenta-colored electrostatic PAPR filter--one for which the manufacturer's user instructions appropriately indicates is not suitable for use in oily environments--was compared with the performance of several mechanical PAPR filters. In tests against both DOP aerosols, the electrostatic PAPR filter showed a significant decrease in performance at DOP loadings exceeding 400 mg, whereas mechanical filters showed no significant change in the performance except at extremely high loadings. The decreased performance of the electrostatic PAPR filter was found to be significantly greater when tested against a neutralized DOP aerosol when compared with a charged DOP aerosol. While laboratory tests show that the filtration efficiency of this electrostatic PAPR filter degrades with exposure to DOP aerosol, the observed laboratory degradation may or may not affect workplace performance, as similar degradation has not been verified in workplace studies. Based on these laboratory results, a proposed method for evaluating high-efficiency PAPR filters is presented. This proposed method would ensure that high-efficiency PAPR filters (> or = 99.97% efficient and magenta in color) meet critical performance criteria when loaded.     

消化内镜中心气溶胶产生及防控策略研究进展

 内镜诊疗操作的侵入性和清洗消毒操作的开放性等特点,使内镜中心已成为气溶胶产生的重点区域,医务人员长期气溶胶暴露后可对人体健康造成巨大危害。本文通过回顾国内外文献,对消化内镜中心的气溶胶来源、医务人员暴露风险以及防控策略等多方面进行综述,以期为内镜医务人员防范职业暴露,保障人体健康提供借鉴意见。     

Aerosol climatology in the northwestern Indian Himalaya: a study based on the radiative properties of aerosol

The present study aims to estimate the shortwave aerosol radiative forcing (SWARF) and their effect on regional climate over Mohal (31.9°N, 77.12°E) in the northwestern Indian Himalaya. The radiative properties of aerosols are measured using multiwavelength radiometer. These measurements are carried out during 2006–2010. Recent studies have shown that the continuously increasing level of aerosols along the elevated slopes of the Indian Himalaya results in many climatic implications. The major climatic effect of aerosol has changed the nature of SWARF, which depends on the single-scattering albedo (SSA). This study reports that the values of SSA are low during winter, which indicates the significant contribution of absorbing aerosols. The large values of SSA was observed during the premonsoon, which signifies notable contribution of scattering aerosols. The largest SWARF at the surface was estimated during the premonsoon, while the smallest was during the monsoon. This study reports that the burden of absorbing aerosols over the Indian region is higher, which results in notable solar heating over India.     

Differential recall as a source of bias in epidemiologic research

Differential recall between compared groups is discussed most often in the context of case-control studies. Cases, compared to controls, are suspected of providing a more complete report of their true exposure to an hypothesized risk factor, thereby biasing upwards the estimate of its effect. The present paper describes how differential recall can arise with any observational design in epidemiology; with any class of study variable, not only exposures; and may inflate or deflate the true value of the estimate of effect size. We list a variety of study designs and questionnaire tactics that aim to remedy these problems. The scope and magnitude of the bias created by differential recall and the efficacy of proposed remedies require further study.     

Tools for assessing quality and susceptibility to bias in observational studies in epidemiology: a systematic review and annotated bibliography

BACKGROUND: Assessing quality and susceptibility to bias is essential when interpreting primary research and conducting systematic reviews and meta-analyses. Tools for assessing quality in clinical trials are well-described but much less attention has been given to similar tools for observational epidemiological studies. METHODS: Tools were identified from a search of three electronic databases, bibliographies and an Internet search using Google. Two reviewers extracted data using a pre-piloted extraction form and strict inclusion criteria. Tool content was evaluated for domains potentially related to bias and was informed by the STROBE guidelines for reporting observational epidemiological studies. RESULTS: A total of 86 tools were reviewed, comprising 41 simple checklists, 12 checklists with additional summary judgements and 33 scales. The number of items ranged from 3 to 36 (mean 13.7). One-third of tools were designed for single use in a specific review and one-third for critical appraisal. Half of the tools provided development details, although most were proposed for future use in other contexts. Most tools included items for selection methods (92%), measurement of study variables (86%), design-specific sources of bias (86%), control of confounding (78%) and use of statistics (78%); only 4% addressed conflict of interest. The distribution and weighting of domains across tools was variable and inconsistent. CONCLUSION: A number of useful assessment tools have been identified by this report. Tools should be rigorously developed, evidence-based, valid, reliable and easy to use. There is a need to agree on critical elements for assessing susceptibility to bias in observational epidemiology and to develop appropriate evaluation tools.     

Autoregression as a means of assessing the strength of seasonality in a time series

Background  

The study of the seasonal variation of disease is receiving increasing attention from health researchers. Available statistical tests for seasonality typically indicate the presence or absence of statistically significant seasonality but do not provide a meaningful measure of its strength.     

Restriction as a method for reducing bias in the estimation of direct effects

The direct effect of a treatment on some outcome is that part of the treatment's effect not referred through a specified covariate intermediate on the pathway between treatment and outcome. Such direct effects are often of primary interest in a data analysis. Unfortunately, standard methods of analysis (for example, stratification or modelling) do not, in general, produce consistent estimates of direct effects whether or not the covariate is ‘controlled’. Robins and co-authors have proposed two methods for estimation of direct effects applicable when reliable information is available on the covariate. We propose a third approach for reducing bias: data restriction. By restricting the analysis to strata of the data in which the effect of treatment on the covariate is small, we can (under certain assumptions) reduce bias in estimating treatment's direct effect. We discuss these points with reference to difference and ratio measures of treatment effect. The approach will sometimes be applicable even with an unmeasured or poorly measured covariate. We illustrate these points with data from an observational study of the effect of hormone replacement therapy on breast cancer. © 1998 John Wiley & Sons, Ltd.     

Consultation letters as a method for assessing in-training performance in a department of medicine.

This study examined the feasibility of using outpatient consultation letters as a means of assessing the clinical performance of clerks and house staff in a large teaching hospital. A total of 222 assessments were obtained based on samples of consultation problems from two clinical services. The method involved a two-stage rating scale based on the performance areas of Data Base, Problem Formulation, Diagnostic Tests, Management and Overall Assessment. The technique was investigated in terms of the objectivity, reliability, validity and efficiency of the performance ratings. Product-moment coefficients were used to assess inter- and intrarater agreement in scoring the consultation letters. These analyses identified a consistent difficulty in assessing the category of Data Base. For the remaining performance categories, interrater coefficients in the range .19-.76 and intrarater coefficients in the range .23-.96 were obtained. Other preliminary findings indicated good potential for a reliable and valid assessment. The method is technically feasible, and is based on a novel and reasonably unobtrusive approach to assessing trainee performance in a clinical setting.     

Assessing bias in a prospective study of diabetes that implemented substitution sampling as a recruitment strategy

ObjectiveStrategies such as reminders are frequently used to maximize baseline recruitment and for this reason are collectively termed “usual practice.” The objective of this study was to investigate substitution sampling as an alternative recruitment strategy.Study Design and SettingsData are from the Living with Diabetes Study, which is a prospective cohort study providing a comprehensive examination of health care utilization. Baseline information was collected for 3,197 of 11,470 eligible individuals between November 2008 and October 2009. Follow-up occurred 12 months after recruitment, with outcome of interest being emergency department attendance. Biases resulting from the two recruitment programs were investigated through the comparison of adjusted logistic regression coefficients and absolute relative biases (ARBs).ResultsCorresponding estimates resulting from both programs were similar except for age (75+ years). This effect was significant (β: −0.59; 95% confidence interval [CI]: −1.04, −0.13) under substitution sampling, but not under “usual practice” (β: −0.36; 95% CI: −0.78, 0.07). Analysis using the ARB metric reinforced similarity, with the Wilcoxon signed-rank test failing to detect significant difference between programs (median difference: −1.01; 95% CI: −5.88, 2.02).ConclusionSubstitution sampling deserves consideration as a recruitment option alongside “usual practice,” as concerns about additional bias may be unwarranted.     

Kernel density estimation as a technique for assessing availability of health services in Nicaragua

Typically, accessibility ratios have been calculated through a simple mathematical division of the number of people in an area by the number of facilities (or staff) in that area. This approach does not take into account the service area of the facility or its proximity to population centers, and is often performed using aggregate numbers for an administrative region. This paper describes an approach to calculating accessibility ratios such as population to facility ratios or population to staff ratios using Kernel density estimation (KDE) within a geographic information system. KDE disperses discrete phenomena across continuous space and is unrestrained by administrative boundaries. Therefore it provides a better representation of the spread of people and services across the landscape. Two types of accessibility ratios are calculated on a national level for Nicaragua: population-per-facility and population-per-staff; the merits of using KDE over traditional approaches are discussed.     

Challenges in incorporating a quality strategy into information systems development efforts

Quality is an essential element of conducting successful information systems (IS) initiatives. While quality is a critical issue, statistics indicate that between one and two thirds of IS projects fail and of the most expensive software projects, about half eventually will be canceled for being out of control. This article examines the three phases of quality management and how these relate to IS development. This article illustrates the challenges faced in incorporating quality into an IS development effort and concludes with observations about the general states of IS development quality.     

Time to pregnancy as a correlate of fecundity: differential persistence in trying to become pregnant as a source of bias

BACKGROUND: Subfecundity is a frequent and often serious problem and it is important to identify its preventable determinants and to monitor fecundity over time. Since follow-up studies are difficult and expensive to conduct, time to pregnancy (TTP) in pregnant women is often used as a surrogate measure of fecundity. TTP data can be retrieved at low costs and they need no valid population registry as a source for sampling. While TTP may serve as a valid surrogate measure in many situations, its validity rests upon a number of assumptions. We have analysed one of these overlooked assumptions, the importance of persistence in trying to become pregnant. METHODS: By means of computer simulations we estimated bias caused by differences in persistence in pregnancy attempts. We investigated whether the assumptions made in the simulation were realistic by using empirical data from a European study. RESULTS: The mean waiting time to pregnancy and other estimates of subfecundity (or infertility) strongly depend upon the persistence of couples in pursuing a pregnancy. We show that even moderate changes in the planning behaviour considerably modify the waiting time distribution. Empirical data confirm that persistence in trying to become pregnant is age-related. CONCLUSIONS: Persistence in pregnancy attempts affects outcome measures of subfecundity in studies based upon TTP in pregnant women. It is likely that the length of time during which couples keep trying to become pregnant is influenced by a number of factors which would probably change over time or be different between populations to be compared.