Definition and assessment of sampling and analytical accuracy.

Two independent definitions for quantifying measurement accuracy and two limiting schemes for their assessment are examined in this paper. Gauss' mean square error MSE is compared to the symmetric-range accuracy A, describing the range of measurements about a measurand. Both measures of accuracy account for systematic error (bias) and imprecision so as to quantify the closeness of estimates to the actual values being measured. Remarkably, it is found that the accuracy functions are closely equivalent for most method applications. Furthermore, details are presented on how to compute confidence limits on measurement accuracy so as to account for error in method evaluation. The confidence limits are qualitatively different in the case that the method undergoes extensive initial evaluation in comparison to a continual re-evaluation at each method application. To this end the statistical theories of tolerance as well as more familiar types of confidence intervals are applied.

Light scattering from deformed droplets and droplets with inclusions. I. Experimental results.

We provide experimental results from the scattering of light by deformed liquid droplets and droplets with inclusions. The characterization of droplet deformation could lead to improved measurement of droplet size as measured by commercial aerodynamic particle-sizing instruments. The characterization of droplets with inclusions can be of importance in some industrial, occupational, and military aerosol monitoring situations. The nozzle assembly from a TSI Aerodynamic Particle Sizer was used to provide the accelerating flow conditions in which experimental data were recorded. A helium-neon laser was employed to generate the light-scattering data, and an externally triggered, pulsed copper vapor laser provided illumination for a droplet imaging system arranged orthogonal to the He-Ne scattering axis. The observed droplet deformation correlates well over a limited acceleration range with theoretical predictions derived from an analytical solution of the Navier-Stokes equation.

Laboratory investigation of the mass stability of sampling cassettes from inhalable aerosol samplers.

A study was conducted to evaluate the mass stability of the materials used in the construction of samplers with internal cassettes for the gravimetric measurement of inhalable aerosol exposures. The internal cassettes from IOM samplers were studied. Results indicate that the mass stability of filters is uniform, but the mass stability of the cassette material may dramatically affect the results of the measurement. Cassettes constructed from plastic exhibited drastic shifts in mass depending on the environmental conditions of their storage. Under room humidity, the plastic cassettes absorbed 1 to 2 mg of water over several days. When these cassettes were placed in a desiccator, they lost mass consistently but did not approach a stable mass. Studies repeated with cassettes made of stainless steel showed negligible mass variability. Based on this study, the use of stainless steel cassettes is recommended for gravimetric determinations of aerosol exposure, although field blanks may in some cases be used for correction of data from plastic cassettes. This study shows the need to evaluate the mass stability of the cassette material of any sampling device where an internal cassette is weighed together with the filter.

Practice management training for pediatric residents.

In 1986, a practice management training program was developed for pediatric house staff. In conjunction with this program, pediatric residents for the following 2 years completed questionnaires regarding their career goals, interests, and perceived competence in practice management. Postgraduate level-3 residents who completed the program felt more competent than postgraduate level-1 residents in all areas of practice management and were more likely to take an active role in managing their practice. There was a significant difference between postgraduate level-1 and level-3 residents who completed the program in several areas: feelings of overall competence in office management, choosing a practice location, office staff, appointment system, billing system, office computer, fee schedules, telephone management, and setting up an office laboratory. Exposure to a practice management program during residency training may better prepare future pediatricians for a successful practice.

Elastic effects of polymer coatings on surface acoustic waves.

Surface acoustic wave (SAW) devices are presently receiving careful scrutiny for applications in chemical sensing as well as in polymer characterization. Gas monitors based on SAW sensors have the potential for miniaturization and high sensitivity to a wide variety of substances. Polymer characterization is applicable to such diverse fields as protective coating design and decontamination of polymers. To better understand the physical mechanisms behind SAW response, the effects of the elastic properties in comparison to the mass loading of polymer coatings on SAW substrates were investigated. A theoretical basis for the effects of vapor-induced swelling or of thermal expansion was established. Compressive tension and its effect on SAW frequencies were found to be simple to describe, if there is no film slippage or polymer flow. The response of quartz substrate SAW crystals coated with polycarbonate and polyimide (glassy polymers) upon exposure to toluene and methanol was measured. Practical problems as to film uniformity, thickness measurement, and environmental control necessary in such measurements are described. Contrary to recent reports in the literature, no significant elastic tightening effect was observed with these vapor/polymer pairs.

Coagulase-negative staphylococci isolated from cerebrospinal fluid shunts: importance of slime production, species identification, and shunt removal to clinical outcome.

We collected and characterized 85 strains of coagulase-negative staphylococci (51 pathogens and 34 contaminants) from cerebrospinal fluid shunts. All isolates were classified by species and characterized by antimicrobial susceptibility and quantitative adherence to plastic tissue culture plates. There were more adherent organisms among pathogens than among contaminants (P less than .01). Species distribution was similar for both groups; however, 20% of the pathogens and none of the contaminants were phosphatase-negative Staphylococcus epidermidis (P less than .05). Resistance to four or more antimicrobial agents was detected in 45% of both groups. Neither species designation nor antimicrobial resistance correlated with clinical outcome. Five (83%) of six infections due to nonadherent (vs. 16 [41%] of 39 due to adherent; P less than .05) coagulase-negative staphylococci were, however, cured with antimicrobial therapy alone. Cure was highly associated with removal of the colonized shunt--38% of infected patients treated with antimicrobial therapy alone were cured, 75% treated with antimicrobial therapy and partial shunt removal were cured, and all treated with antimicrobial therapy and total shunt replacement were cured.

Gardnerella vaginalis in prepubertal girls.

A prospective study was established to determine the significance of the isolation of Gardnerella vaginalis from the vagina in prepubertal children. Two hundred fifty-six children were enrolled. Group 1 consisted of 137 children who had been victims of sexual abuse; group 2, forty-eight children with genitourinary complaints and no history of sexual abuse; and group 3, seventy-one children with no genitourinary complaints and no history of sexual abuse. Gardnerella vaginalis was isolated from 20 patients (14.6%) in group 1 and five (4.2%) of 119 control patients from groups 2 and 3. Within group 1, G vaginalis was more likely to be isolated from children with a history of multiple episodes of sexual abuse than those with a single episode. Gardnerella vaginalis was not associated with any other historical, physical, or laboratory findings, including vaginal erythema or vaginal discharge.

Diffusive samplers using longitudinal sorbent strips.

Longitudinal strip diffusive samplers (often employing color-change reactants) were analyzed from a theoretical viewpoint. Calculation was carried out analytically in terms of varying effective sampling length for a sampler of quite general geometry. A relationship between exposure (or the time-weighted average of the concentration in air) and analyte mass sampled was derived. Modifications of this relationship as well as estimates of the effect of sampler lag were developed for samplers which employed a semipermeable entrance membrane. Additionally, the detailed concentration distribution and analyte streamlines are given for a specific, idealized sampler geometry.

Critique of 1985 ACGIH report on particle size-selective sampling in the workplace.

The criteria recently proposed by ACGIH for judging the acceptability of respirable and other dust fraction samplers are analyzed. Implications on the sampling of workplace aerosol are determined. With the consideration of both bias and imprecision, the overall accuracy limited by the criteria is estimated for the sampling of coal mine dust as characterized by various researchers. The accuracy limits thus found appear to be excessively broad. As an example with actual workplace dust distributions in the sampling of a single aerosol (mass median diameter = 18.6 micrometers and geometric standard deviation = 2.3) with respirable dust concentration near 2 mg/m3, two samplers acceptable according to the proposed criteria could be found giving respirable dust measurements equal to 0.71 mg/m3 and 4.3 mg/m3 (even after excluding 5% of the low and high measurements from each sampler, respectively). Large variation in samplers acceptable according to the criteria is found for many other distributions as well; this indicates that tighter requirements are necessary. Seldom attained are both the single-sample +/- 25% accuracy at the 95% confidence level required of sampling/analytical methods endorsed by the National Institute for Occupational Safety and Health (NIOSH) and the tighter ISO dust fraction measurement requirement that 67% of the measurements of a sampled dust fall within 10% of a true value. Suggestions are given for sharpening the criteria without eliminating all samplers from acceptability.

Use of tracer gas technique for industrial exhaust hood efficiency evaluation--where to sample?

A tracer gas technique using sulfur hexafluoride (SF6) was developed for the evaluation of industrial exhaust hood efficiency. In addition to other parameters, accuracy of this method depends on proper location of the sampling probe. The sampling probe should be located in the duct at a minimum distance from the investigated hood where the SF6 is dispersed uniformly across the duct cross section. To determine the minimum sampling distance, the SF6 dispersion in the duct in fully developed turbulent flow was studied at four duct configurations frequently found in industry: straight duct, straight duct-side branch, straight duct-one elbow, and straight duct-two elbows combinations. Based on the established SF6 dispersion factor, the minimum sampling distances were determined as follows: for straight duct, at least 50 duct diameters; for straight duct-side branch combination, at least 25 duct diameters; for straight duct-one elbow combination, 7 duct diameters; and for straight duct-two elbow combination, 4 duct diameters. Sampling at (or beyond) these distances minimizes the error caused by the non-homogeneous dispersion of SF6 in the duct and contributes to the accuracy of the tracer gas technique.

Ketoconazole and candidiasis: a controlled study.

A double-blind, placebo-controlled study was undertaken to determine the efficacy of ketoconazole in the treatment of candidiasis. The drug was administered orally in the dosage of 200 mg/m2 of body surface per day for two weeks to cancer patients with oral candidiasis. Randomization in a 2:1 ratio provided 36 patients treated with ketoconazole and 20 managed with a placebo. Regression of visible lesions was achieved in 26 (72%) of 36 ketoconazole-treated and four (20%) of 20 untreated patients; eradication of culturable organisms occurred in 12 (36%) of 33 ketoconazole-treated and one (7%) of 14 untreated patients; and resolution of lesions plus eradication of Candida albicans occurred in nine (25%) of 36 ketoconazole-treated and one (5%) of 20 untreated patients. Although the therapeutic efficacy of ketoconazole was demonstrated for oropharyngeal candidiasis, the magnitude of its efficacy was less than that desired.

Computed tomography of hepatic and splenic fungal abscesses in leukemic children.

Six hundred fifty-eight abdominal computed tomography scans of 275 children with cancer were retrospectively studied for evidence of multiple hepatic or splenic "abscess-like" lesions. Seven patients, all with subsequently confirmed fungal disease, were found to have such lesions. In addition to acute leukemia, all patients had prolonged fever not responsive to antibiotics, had neutropenia (less than 500 neutrophils per mm3) and had received anticancer chemotherapy for up to 4 weeks before the positive computed tomography scans. We conclude that the presence of multiple well-circumscribed hepatic or splenic lesions on the abdominal computed tomography scan of a febrile, neutropenic, immunosuppressed patient not responding to antibiotics and with no other source of infection is strong evidence for systemic fungal infection. However, the absence of such lesions may not exclude the diagnosis of systemic mycosis.