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PubMed2004

[Krigle estimation and its simulated sampling of Chilo suppressalis population density].

In order to draw up a rational sampling plan for the larvae population of Chilo suppressalis, an original population and its two derivative populations, random population and sequence population, were sampled and compared with random sampling, gap-range-random sampling, and a new systematic sampling integrated Krigle interpolation and random original position. As for the original population whose distribution was up to aggregative and dependence range in line direction was 115 cm (6.9 units), gap-range-random sampling in line direction was more precise than random sampling. Distinguishing the population pattern correctly is the key to get a better precision. Gap-range-random sampling and random sampling are fit for aggregated population and random population, respectively, but both of them are difficult to apply in practice. Therefore, a new systematic sampling named as Krigle sample (n = 441) was developed to estimate the density of partial sample (partial estimation, n = 441) and population (overall estimation, N = 1500). As for original population, the estimated precision of Krigle sample to partial sample and population was better than that of investigation sample. With the increase of the aggregation intensity of population, Krigel sample was more effective than investigation sample in both partial estimation and overall estimation in the appropriate sampling gap according to the dependence range.

Algorithms↗
PubMed2004

An efficient virus concentration method and RT-nested PCR for detection of rotaviruses in environmental water samples.

Water samples were concentrated by the modified adsorption-elution technique followed by speedVac reconcentration of the filter eluates. Reverse transcriptase-nested polymerase chain reaction (RT-nested PCR) was used to detect rotavirus RNA in concentrates of the water. The detection limit of the rotavirus determined by RT-nested PCR alone was about 1.67 plaque forming units (PFU) per RT-PCR assay and that by RT-nested PCR combined with concentration from 1l seeded tap water sample was 1.46 plaque forming units per assay. Water samples were collected from various sources, concentrated, and determined rotavirus RNA. Of 120 water samples, rotavirus RNA was detected in 20 samples (16.7%); 2/10 (20%) of the river samples, 8/30 (26.7%) of the canal samples, and 10/40 (25%) of the sewage samples but was not found in any tap water samples (0/40). Only three water samples were positive for rotavirus antigen determined using an enzyme-linked immunosorbent assay (ELISA). Alignment analysis of the sequenced PCR product (346-bp fragment) was performed in eight rotavirus-positive samples using the rotavirus sequence deposited in the GenBank. All samples gave the correct VP7 sequence. Results of analysis showed two samples similar to human rotavirus (97-98%), five similar to rotavirus G9 sequence (94-99%), and one sample similar to animal rotavirus (97%). PCR inhibitors were not observed in any concentrated water samples. In all 20 (of 120) samples where rotaviruses were found, fecal coliforms including Escherichia coli were also found, but of the samples testing negative for rotaviruses, 76 were fecal coliforms positive and 69 were E. coli positive. The combination of the virus concentration method and RT-nested PCR described below made it possible to effectively detect rotaviruses in environmental water samples.

Reverse Transcriptase Polymerase Chain Reaction↗
PubMed1998

Short-term variability and sampling distribution of various parameters of urinary albumin excretion in patients with non-insulin-dependent diabetes mellitus.

We determined the degree of variability and sampling distribution of several commonly used parameters of microalbuminuria in patients with non-insulin-dependent diabetes mellitus (NIDDM) and proposed a sampling strategy for estimating the level of albuminuria. Four patients with NIDDM with previously documented microalbuminuria collected 30 consecutive split (overnight and daytime) 24-hour urine samples (experiment A). These samples were analyzed for total 24-hour albumin excretion; daytime, overnight, and 24-hour albumin concentration; and daytime, overnight, and 24-hour albumin-to-creatinine ratio. In a second experiment (B), 10 patients collected 10 consecutive overnight urine samples. Finally, a total of 300 separate triplicate urine samples were analyzed for the variability of 24-hour albumin excretion (100 samples) and albumin-to-creatinine ratios in 24-hour urine (100 samples) and overnight urine (100 samples). We found that the sampling distribution shape of all parameters of albuminuria is positively skewed, without consistent evidence of log-normality. When two methods were used for quantifying day-to-day variability (the interquartile range/median ratio and the chance of a single measurement being >50% off the actual value of albuminuria), the overnight albumin-to-creatinine ratio is the least-variable parameter of albuminuria, scoring 0.38% and 10% on both methods, respectively, in experiment A. Collecting multiple samples of overnight urine improves accuracy. The largest gain in precision in estimating the actual value of albuminuria is obtained for sample sizes of three and five and does not increase with nonconsecutive sampling of urine. Based on the combined data from experiments A and B, the expected mean deviation of the median of three and five overnight samples from the actual level of the overnight albumin-creatinine ratio is 17.9% and 12.1%, respectively. An analysis of variability in three sets of 100 triplicate 24-hour urine samples shows that the overnight albumin-to-creatinine ratio is a significantly more-constant parameter of microalbuminuria than the amount of albumin excreted in 24 hours or the albumin-to-creatinine ratio in 24-hour urine (p < 0.05). We concluded that the parameters of diabetic albuminuria have positively skewed, non-log-normal sampling distributions. The overnight albumin-to-creatinine ratio is the least-variable parameter of microalbuminuria. We recommend collecting three consecutive early morning urine samples, using the median value of the albumin-to-creatinine ratio in these samples for quantifying albuminuria.

Aged↗
PubMed2005

Self-sampling is associated with increased detection of human papillomavirus DNA in the genital tract of HIV-seropositive women.

BACKGROUND: Analysis of self-collected swab samples from the genital tract could improve accrual and retention of women in studies of human papillomavirus (HPV) infection and precancerous cervical lesions. Self-collected vaginal swab specimens and physician-collected cervical swab specimens were compared for detection and typing of HPV DNA in 158 HIV-seropositive women. METHODS: Paired samples were collected for 157 participants. Beta-globin was not detected in 6 (3.3%) physician-collected specimens and 8 (4.3%) self-obtained specimens collected from 11 women, leaving 146 paired samples suitable for PCR analysis. HPV DNA was amplified with the HPV primers PGMY09 and PGMY11 and typed using the line blot assay. RESULTS: HPV DNA was detected more frequently in self-collected samples (95 [65.1%] of 146), compared with physician-collected samples (78 [53.4%] of 146) (P = .04). Self-collected samples contained a greater number of types (mean +/- SD, 1.60 +/- 1.80 types; 95% confidence interval [CI], 1.31-1.90), compared with physician-collected samples (mean +/- SD, 1.25 +/- 1.66 types; 95% CI, 0.98-1.52) (P = .04). A good agreement between sampling methods was achieved for detection of any HPV DNA (kappa = 0.73; 95% CI, 0.58-0.89), high-risk types (kappa = 0.84; 95% CI, 0.68-0.99), and low-risk types (kappa = 0.71; 95% CI, 0.67-0.75). Agreement between sampling methods for detection of HPV DNA was found for 24 (88.8%) of 27 follow-up samples collected from a total of 20 women. A comparison of samples collected at consecutive visits revealed agreements for detection of any HPV DNA, detection of high-risk HPV, and HPV typing results between visits of 88.9% (24 of 27 samples), 81.5% (22 of 27), and 55.5% (15 of 27), respectively, for physician-collected samples, and 96.3% (26 of 27 samples), 92.6% (25 of 27), and 55.5% (15 of 27), respectively, for self-collected samples. CONCLUSION: Analysis of self-collected vaginal swab samples improved the detection rate of HPV, suggesting that such samples might be of greater value than physician-obtained samples in studies of HPV transmission.

Adolescent↗
PubMed2000

A new method of post-dialysis blood urea sampling: the 'stop dialysate flow' method.

BACKGROUND: A standardized practical method of post-dialysis blood sampling is required to improve the precision of using urea kinetics in the evaluation of haemodialysis dose and to permit comparative audit. The methods recommended in the Renal Association and Dialysis Outcomes Quality Initiative (DOQI) guidelines reduce the blood pump speed to a low rate at the end of haemodialysis before blood sampling after 10 and 15 s respectively. However, these 'low flow' methods compensate only partially for cardiopulmonary recirculation and may be impractical in routine practice because they involve sequential steps and require accurate timing of sampling. Therefore we have evaluated an alternative method of stopping only the dialysate flow at the end of the haemodialysis session before performing post-dialysis blood sampling. METHODS: The study was performed in three phases. Serial measurements of blood urea were obtained from arterial and venous samples taken at times 0, 30, 60, 120, 180, 240, 300 and 360 s after stopping dialysate flow and leaving the extracorporeal blood flow rate unchanged at the end of the haemodialysis session in 10 patients. A peripheral venous sample was also taken from the contralateral arm at 0 s to reflect body water urea concentration at the end of dialysis without the effect of access recirculation and with a minimal effect of cardiopulmonary recirculation. The same haemodialysis prescription was repeated in the same 10 patients using the Renal Association method to permit comparison between the two methods. The practical use of the 'stop dialysate flow' method was then evaluated in 117 regular haemodialysis patients undergoing routine monthly assessment of dialysis adequacy and compared with sampling immediately post-dialysis. RESULTS: Within 4 min of stopping the dialysate flow there was no difference between the blood urea concentrations of arterial and venous samples, indicating cessation of diffusion across the dialysis membrane. Also the blood urea concentrations in all of the arterial and venous samples between 4 and 6 min were constant and were equivalent to the blood urea concentration of the peripheral venous sample taken at 0 s. These data suggest that post-dialysis blood sampling may be performed 5 min after stopping dialysate flow at the end of the haemodialysis session. In contrast, the blood urea concentration in the post-dialysis samples obtained using the Renal Association method were lower than the contralateral arm blood urea concentration taken at 0 s (0.31+/-0.42; P<0.05) and consequently the percentage URR was higher (1.35+/-1.84%). In 117 patients the post-dialysis blood urea sample 5 min after stopping dialysate flow averaged 5.49+/-2.11 mmol/1 compared with 5.07+/-2.05 mmol/l immediately after the end of the haemodialysis session (P<0. 0001). This was equivalent to a reduction in URR from 71.7+/-8.3% with sampling immediately post-dialysis to 69.1+/-9.3% with the 'stop dialysate flow' method. CONCLUSIONS: This study shows that there is a window period between 4 and 6 min after stopping dialysate flow at the end of the haemodialysis session when the blood urea concentration in a sample taken from any part of the extracorporeal circuit remains constantly within the co-efficient of variation of laboratory measurement, and is equivalent to a peripheral venous sample taken immediately at the end of the dialysis session. A 'stop dialysate flow' method with blood sampling after 5 min offers several advantages over 'slow flow' methods, since it allows for cardiopulmonary as well as access recirculation, does not require precise timing of blood sampling, and is simple to perform in a busy renal unit. For these reasons the 'stop dialysate flow' method may be used for routine monitoring of the adequacy of delivered haemodialysis and for comparative audit among haemodialysis centres.

Adult↗
PubMed2004

Maximum a posteriori Bayesian estimation of epirubicin clearance by limited sampling.

AIMS: To develop a limited sampling strategy for estimation of epirubicin clearance. METHODS: The data set comprised 1051 concentrations measured in 105 patients with advanced or metastatic breast cancer treated with epirubicin alone. Ten limited sampling designs comprising two or three blood samples were proposed, taken at times identified by D-optimality from population pharmacokinetic parameter estimates. The data set was then truncated to include the sampling times for each of the designs. MAP Bayesian estimates of clearance were generated for each design and compared with clearance estimates obtained using all the data. The limited sampling designs were also validated using a separate data set obtained from 18 patients with either breast cancer or hepatocellular carcinoma. The sensitivity of the best limited sampling designs to sample time recording errors of 0-10% or 10-20% was then assessed using a simulated data set including 200 patients. RESULTS: The optimum sampling times were: end of the injection and 18 min, 40 min, 3 h, 10 h and 48 h after the start of the injection. The best three-sample design included samples at 40 min, 3 h and 48 h and gave unbiased estimates of clearance with an imprecision of 9.1% (95% CI 7.3, 10.5). The best two sample design included samples at 3 and 48 h and gave unbiased estimates of clearance with an imprecision of 12.4% (95% CI 9.6, 14.6). Using the validation data set, these two and three sample designs gave unbiased estimates of clearance with an imprecision of 5.6% (95% CI 3.7, 7.0) and 4.2% (95% CI 2.6, 5.3), respectively. Simulations that included 0-10% or 10-20% errors in the recording of the blood sampling times had negligible effects on the bias and imprecision of clearance estimates. CONCLUSIONS: Limited sampling designs have been identified and validated that estimate epirubicin clearance with adequate precision and without bias from two or three blood samples. These designs also allow flexibility in blood sample collection and are robust with regard to sample time recording errors.

Adult↗
PubMed2003

Empirical modelling of population sampling: lessons for designing sentinel surveillance.

BACKGROUND: In order to consider the practical viability of 1% sentinel area surveillance for health information in resource-poor settings where complete registration is unrealistic, the effects of different sampling procedures on the representativeness of 1% population samples have been investigated. METHODS: Using the 1991 census of England as a basis for modelling, 20 1% samples, each incorporating seven key parameters, were drawn at random from the overall dataset by each of eight different sampling procedures. Each sample was compared with the 'gold standard' of the overall census results, enabling comparisons between the different sampling procedures. RESULTS: Representativeness of the 1% samples varied considerably between parameters and sampling procedures. At one extreme, the proportion of males in the population was distributed such that different sampling methods had little effect. On the other hand, samples of a heterogeneous parameter such as the proportion of non-whites in the population depended greatly on the procedure used. Sampling smaller administrative units tended to be more accurate. However, sampling units using probability proportional to size generally gave less representative samples. Stratifying urban and rural populations in the samples had little effect. Multistage sampling, emulating typical demographic surveillance sites, also generally gave less representative samples. CONCLUSIONS: It is possible to achieve representative data by taking 1% of a national population in a sentinel surveillance approach, but sampling design can have an important influence on the outcome. This modelling supports the concept of 1% sentinel surveillance for health information in poorer settings, where complete data are unavailable.

Censuses↗
PubMed1992

Sampling in epidemiological research: a case study of the prevalence of brucellosis in Saudi Arabia.

The superficial description in biomedical journals of sampling methods used in epidemiological studies of the prevalence of some diseases can be attributed to shallow knowledge of basic sampling techniques. The population of interest in most community surveys is usually very large and resources and time available limited, so that researchers have little or no choice but to study a sample of the population. One of the basic principles of sampling is the avoidance of bias, guaranteed by taking a random sample. But the term 'random sample' has often been misinterpreted as synonymous with 'haphazard sample', taking a sample without a definite pattern. It is re-emphasised that a random sample is a probability sample that gives every unit in the population a known probability of being selected in the sample. The procedures for taking a random sample for a nationwide study in the Kingdom of Saudi Arabia are not easy because of the structure of the population, and therefore require more complex sampling methods like the stratified cluster sampling. It is also necessary in a stratified sample to calculate estimated persons affected by a condition for each selected subgroup of the population before obtaining the overall prevalence rate. A proper understanding and use of appropriate sampling techniques is most likely to result in the most desired representative sample, and guarantees that some underlying assumptions for inferential statistics will be satisfied.

Brucellosis↗
PubMed2004

Changes in toxicity and genotoxicity of industrial sewage sludge samples containing nitro- and amino-aromatic compounds following treatment in bioreactors with different oxygen regimes.

GOALS, SCOPE AND BACKGROUND: From 2005, deposition of organic waste will be banned in Sweden. Likewise, in Germany and Austria, similar bans are being planned, and further countries will probably follow. Thus, there is a need to develop new methods and to refine established techniques for sludge management in the whole of the European Union. For this end, there is also an urgent need for appropriate ecotoxicological approaches to elucidate and assess the hazard potential of sewage sludge. Therefore, the present study was designed to assess the capacity of various established sludge treatment methods using different oxygen regimes to degrade recalcitrant nitro-substituted organic compounds and reduce their toxicity. Sewage sludge samples from a wastewater treatment plant in Sweden (Cambrex Karlskoga AB, industrial area Björkborn) receiving wastewater from industries manufacturing pharmaceutical substances, chemical intermediates and explosives were processed with different sludge treatment methods. Among other treatment methods, bioreactors (for anaerobic and aerobic sludge treatment) were used. In the present investigation, a battery of in vitro bioassays was employed to compare the cytotoxic and genotoxic potentials of different fractions of sludge samples in order to elucidate whether the treatments were suitable to reduce the toxicity of the sludge. METHODS: In order to investigate the cytotoxicity of the extracts of treated and untreated sludge samples, the acute cytotoxicity test with the permanent cell line RTL-W1 was used. Genotoxicity was tested by means of the comet assay (single cell gel electrophoresis) with RTL-W1 cells, and mutagenicity was assessed with the Ames test using the Salmonella typhimurium strains TA98, TA98NR and TA100. Sludge toxicity was tested in different fractions of organic extracts produced by acetone and hexane extractions. The subsequent clean-up procedure (silica gel chromatography and elution with hexane and dichloromethane) resulted in two fractions, a lipophilic hexane-fraction and a semi-lipophilic dichloromethane-fraction. For the genotoxicity and mutagenicity tests, these fractions were reunited at equal ratios. RESULTS AND DISCUSSION: The acute cytotoxicity test with RTL-W1 cells revealed a high cytotoxic potential for the semi-lipophilic DM-fractions of all sludge samples with NR50 values (= effective concentration for 50% cell death in the neutral red test) from 8.9 up to 20 mg sludge d.w./ml medium. A low cytotoxic potential for the hexane fractions of the untreated sludge samples (NR50 400 to > 400 mg sludge d.w./ml medium) was observed, whereas the hexane fractions of the treated sludge samples showed elevated cytotoxicity increasing further with treatment in the bioreactors. The comet assay indicated that three out of eight of the reunited fractions had a significant genotoxic potential. Whereas the genotoxic potential of one sample treated anaerobically was very high with an induction factor of 11.6, a similar sample (taken from the same anaerobic reactor four months later) and one untreated sample showed lower potentials. The samples treated in another anaerobic bioreactor as well as the samples treated aerobically showed no genotoxic potential. Results indicate that aerobic treatment was basically adequate for reducing the genotoxicity of the sludge, whereas anaerobic treatment was only partly useful for reduction of genotoxicity. The Ames test revealed a very high mutagenic potential for the reunited fractions of the untreated sludge samples with strain TA98 (maximum induction factors (IFmax) up to 45) and a relatively high potential for one of the samples treated aerobically (S2, IFmax = 18 (TA98, S9-)), thus documenting the suitability of both anaerobic and aerobic treatments to reduce the mutagenicity of the samples, however, with the aerobic treatment being less effective. CONCLUSIONS: Overall, none of the microbiological treatments for wastewater sludge in bioreactors was found to be ideal for general toxicity reduction of the sludge samples. Whereas cytotoxicity of the sludge increased or levelled off in most cases following either treatment, genotoxicity both increased or decreased after anaerobic treatment, depending on the specific sample. However, mutagenicity could generally be reduced by anaerobic treatment and, to a lesser degree, by aerobic treatment. RECOMMENDATIONS AND PERSPECTIVES: The complex modification of the diverse damage potentials of sludge sample extracts by use of an in vitro biotest battery following treatment for toxicity reduction in bioreactors showed that considerations of different toxicological endpoints is essential for an adequate hazard assessment. Whereas in the case of cytotoxicity reduction, the reactors proved ineffective, mutagenicity could be reduced significantly at least in some cases in this case study.

Biological Assay↗
PubMed1999

Genotyping for DQA1 and PM loci in urine using PCR-based amplification: effects of sample volume, storage temperature, preservatives, and aging on DNA extraction and typing.

Urine is often the sample of choice for drug screening in aviation/general forensic toxicology and in workplace drug testing. In some instances, the origin of the submitted samples may be challenged because of the medicolegal and socioeconomic consequences of a positive drug test. Methods for individualization of biological samples have reached a new boundary with the application of the polymerase chain reaction (PCR) in DNA profiling, but a successful characterization of the urine specimens depends on the quantity and quality of DNA present in the samples. Therefore, the present study investigated the influence of storage conditions, sample volume, concentration modes, extraction procedures, and chemical preservations on the quantity of DNA recovered, as well as the success rate of PCR-based genotyping for DQA1 and PM loci in urine. Urine specimens from male and female volunteers were divided and stored at various temperatures for up to 30 days. The results suggested that sample purification by dialfiltration, using 3000-100,000 molecular weight cut-off filters, did not enhance DNA recovery and typing rate as compared with simple centrifugation procedures. Extraction of urinary DNA by the organic method and by the resin method gave comparable typing results. Larger sample volume yielded a higher amount of DNA, but the typing rates were not affected for sample volumes between 1 and 5 ml. The quantifiable amounts of DNA present were found to be greater in female (14-200 ng/ml) than in male (4-60 ng/ml) samples and decreased with the elapsed time under both room temperature (RT) and frozen storage. Typing of the male samples also demonstrated that RT storage samples produced significantly higher success rates than that of frozen samples, while there was only marginal difference in the DNA typing rates among the conditions tested using female samples. Successful assignment of DQA1 + PM genotype was achieved for all samples of fresh urine, independent of gender, starting sample volume, or concentration method. Preservation by 0.25% sodium azide was acceptable for sample storage at 4 degrees C during a period of 30 days. For longer storage duration, freezing at -70 degrees C may be more appropriate. Thus, the applicability of the DQA1 + PM typing was clearly demonstrated for individualization of urine samples.

DNA↗
PubMed2002

Evaluation of Petri dish sampling for assessment of cat allergen in airborne dust.

BACKGROUND: Dust reservoir sampling is the most commonly used method for assessment of indirect allergen exposure. Because assessment of personal exposure using person-carried pumps is time-consuming and expensive we evaluated the Petri dish sampling method for measurement of airborne cat allergen in classrooms. METHODS: Petri dish sampling was evaluated in three study parts. Part I: by comparison between Petri dish sampling and personal air sampling in 44 classrooms with many (> or = 20%) and few (< or = 10%) cat owners and by additional Petri dish sampling in 40 pet-free homes. Part II: by sampling with duplicate Petri dishes in 28 classrooms. Part III: by sampling in three classrooms at four sampling heights during different sampling times. All samples were analyzed for cat allergen (Fel d 1) content with a monoclonal antibody two-site ELISA (enzyme linked immunosorbent assay), using signal amplification when necessary. RESULTS: There was a significant correlation between Petri dish sampling and personal air sampling (r = 0.66; P < 0.0001). Levels were five-fold higher in classes with many cat owners than in classes with few cat owners, regardless of method. A corresponding difference was found in the homes. Duplicate sample values were in fair agreement (Bland-Altman test) and were correlated (r = 0.77; P < 0.0001). Cumulative levels collected weekly in one Petri dish were lower than using five daily Petri dishes, regardless of sampling height. CONCLUSIONS: Petri dish sampling can be useful as an alternative method to personal air sampling of airborne allergens.

Air Pollution, Indoor↗
PubMed2003

Transect sampling to enhance efficiency of corn rootworm (Coleoptera: Chrysomelidae) monitoring in corn.

Crop monitoring for adult corn rootworms, Diabrotica virgifera virgifera LeConte and Diabrotica barberi Smith and Lawrence, remains the best means to assess fields at risk from this pest if replanted to corn, Zea mays (L.). Improvements in sampling methodology, including the development of a sequential sampling plan, have reduced the minimum sampling time required to make a management decision to 20 min or less per field per visit. However, many growers and crop consultants still find this time commitment a constraint to repeated scouting. A common currently used sampling method involves systematically covering most of the field following a "W" pattern. The feasibility of replacing the current sampling pattern with a simpler and less time-consuming transect (straight line) pattern was assessed. When sampling methods were compared, computer simulations demonstrated that treatment decisions based on transect sampling would have an acceptably low error rate averaging 10% over a range of realistic corn rootworm densities (0-2 adults per plant). This error rate represented a decrease in accuracy of <1% compared with systematic sampling. Field trials using transect, systematic, and random sampling in each field were used to compare the categorization of adult corn rootworm densities into "above" or "below" threshold with a sequential sampling plan. Efficiency measured in time to reach a decision, number of corn plants evaluated, and time divided by plants observed were compared between sampling methods. The three methods did not differ significantly in the number of plants evaluated or in the categorization of corn rootworm populations. Transect sampling resulted in a significantly shorter time divided by plants observed (38 s), than either systematic (78 s), or random sampling methods (166 s). Based on these results transect sampling reduces sampling time 51% compared with systematic sampling and thus could be used to reduce total sampling times substantially.

Agriculture↗
PubMed2005

Easy-to-use, accurate and flexible individualized Bayesian limited sampling method without fixed time points for ciclosporin monitoring after liver transplantation.

BACKGROUND: New methods to estimate the systemic exposure to ciclosporin such as the level 2 h after dosing and limited sampling formulas may lead to improved clinical outcome after orthotopic liver transplantation. However, most strategies are characterized by rigid sampling times. AIM: To develop and validate a flexible individualized population-pharmacokinetic model for ciclosporin monitoring in orthotopic liver transplantation. METHODS: A total of 62 curves obtained from 31 patients at least 0.5 year after orthotopic liver transplantation were divided into two equal groups. From 31 curves, relatively simple limited sampling formulas were derived using multiple regression analysis, while using pharmacokinetic software a two-compartment population-pharmacokinetic model was derived from these same data. We then tested the ability to estimate the AUC by the limited sampling formulas and a different approach using several limited sampling strategies on the other 31 curves. The new approach consists of individualizing the mean a priori population-pharmacokinetic parameters of the two-compartment population-pharmacokinetic model by means of maximum a posteriori Bayesian fitting with individual data leading to an individualized population-pharmacokinetic limited sampling model. From the individualized pharmacokinetic parameters, AUC(0-12h) was calculated for each combination of measured blood concentrations. The calculated AUC(0-12h) both from the limited-sampling formulas and the limited-sampling model were compared with the gold standard AUC(0-12h) (trapezoidal rule) by Pearson's correlation coefficient and prediction precision and bias were calculated. RESULTS: The AUC(0-12h) value calculated by individualizing the population-pharmacokinetic model using several combinations of measured blood concentrations: 0 + 2 h (r(2) = 0.94), 0 + 1 + 2 h (r(2) = 0.94), 0 + 1 + 3 h (r(2) = 0.92), 0 + 2 + 3 h (r(2) = 0.92) and 0 + 1 + 2 + 3 h (r(2) = 0.96) had excellent correlation with AUC(0-12h), better than limited sampling formulas with less than three sampling time points. Even trough level with limited sampling method (r(2) = 0.86) correlated better than the level after 2 h of dosing (r(2) = 0.75) or trough level (r(2) = 0.64) as single values without limited sampling method. Moreover, the individualized population-pharmacokinetic model had a low prediction bias and excellent precision. CONCLUSION: Multiple rigid sampling time points limit the use of limited sampling formulas. The major advantage of the Bayesian estimation approach presented here, is that blood sampling time points are not fixed, as long as sampling time is known. The predictive performance of this new approach is superior to trough level and that after 2 h of dosing and at least as good as limited sampling formulas. It is of clear advantage in busy out-patient clinics.

Adult↗
PubMed2006

Dust sampling methods for endotoxin - an essential, but underestimated issue.

Exposure to farming environment in early life has been associated with lower risk for allergic diseases possibly caused by increased exposure to endotoxin. The aims of this study were to compare the reproducibility of different sampling methods for endotoxin, and to determine whether environmental characteristics have different effect on endotoxin levels of different sample types. The reproducibility of sampling methods (bed dust, floor dust, vacuum cleaner dust bag dust, settled dust and air samples) was studied with repeated sampling (five visits during 1 year) in five farming and five urban homes. To examine determinants of endotoxin for different types of dust sample, sampling was conducted once in 12 farming and 17 urban homes. Endotoxin was analyzed using Limulus Amebocyte Lysate assay. Bed dust samples had the best reproducibility (intraclass correlation, ICC=66%), but the difference between farming and non-farming homes was not clear with this sample type. The reproducibility of floor (ICC=52%) and settled dust (ICC=51%) was moderate. With these sample types the difference between farming and non-farming homes was clear. Settled dust had some seasonal variation. Based on this study, the best compromise for sampling for endotoxin appears to be floor dust sample followed by bed and settled dust samples. Practical Implications Endotoxins have been widely measured, even though the validity of different sample types to reflect the endotoxin exposure level of an indoor environment is poorly known. This study shows that bed dust samples have the best reproducibility, but they do not reflect the differences in exposure due to environmental factors such as farming. Floor dust samples with moderate reproducibility may be the best choice for sampling of endotoxin in large field studies.

Air Pollution, Indoor↗
PubMed2005

The adequacy of sample type/weight and incubation period on detection of Salmonella spp. in slaughter cattle.

The purpose of this study was to examine the adequacy of different sample types (fecal and rumen content), rumen-content sample weight (1, 10, and 25 g), and incubation period on the detection of Salmonella spp. in grass-fed beef cattle at slaughter. The culture technique was the same for all samples and followed the Australian Standard (AS 1766.2.5-1991). Sample adequacy was defined as the ratio between the overall prevalence, as obtained from samples identified as positive by any sample type/weight, and the estimated prevalence, as obtained from samples identified as positive by a particular sample type/weight. Sample adequacy reflects the likelihood of a sample of a particular type and weight to contain the organism of interest and hence is related to the sensitivity of the diagnostic test. It was found that sample adequacy differed between sample types and weights: 37.5% for both a 10-g fecal sample and a 1-g rumen sample, 77.1% for a 10-g rumen sample, and 79.2% for a 25-g rumen sample. On this basis, it is strongly recommended that sample type and weight be considered in the design of studies that aim to quantify Salmonella contamination in cattle.

Animals↗
PubMedDate not supplied

Testing shelled corn for aflatoxin, Part III: evaluating the performance of aflatoxin sampling plans.

The effects of changes in sample size and/or sample acceptance level on the performance of aflatoxin sampling plans for shelled corn were investigated. Six sampling plans were evaluated for a range of sample sizes and sample acceptance levels. For a given sample size, decreasing the sample acceptance level decreases the percentage of lots accepted while increasing the percentage of lots rejected at all aflatoxin concentrations, and decreases the average aflatoxin concentration in lots accepted and lots rejected. For a given sample size where the sample acceptance level decreases relative to a fixed regulatory guideline, the number of false positives increases and the number of false negatives decreases. For a given sample size where the sample acceptance level increases relative to a fixed regulatory guideline, the number of false positives decreases and the number of false negatives increases. For a given sample acceptance level, increasing the sample size increases the percentage of lots accepted at concentrations below the regulatory guideline while increasing the percentage of lots rejected at concentrations above the regulatory guideline, and decreases the average aflatoxin concentration in the lots accepted while increasing the average aflatoxin concentration in the rejected lots. For a given sample acceptance level that equals the regulatory guideline, increasing the sample size decreases misclassification of lots, both false positives and false negatives.

Aflatoxins↗
PubMed2006

Detection of Cryptosporidium oocysts in water: effect of the number of samples and analytic replicates on test results.

Due to the small number of Cryptosporidium oocysts in water, the number of samples taken and the analyses performed can affect the results of detection. In this study, 42 water samples were collected from one watershed during 20 storm events over 1 year, including duplicate or quadruplicate samples from 16 storm events. Ten samples from four events had three to eight subsamples. They were processed by EPA method 1623, and Cryptosporidium oocysts present were detected by immunofluorescent microscopy or PCR. Altogether, 24 of 39 samples (47 of 67 samples and subsamples) analyzed by microscopy were positive for Cryptosporidium. In contrast, 36 of 42 samples (62 of 76 samples and subsamples) were positive by PCR, including 10 microscopy-negative samples (13 microscopy-negative samples and subsamples). Six of the 24 microscopy-positive samples were negative by PCR, and all samples had one or less oocyst in a 0.5-ml packed pellet volume calculated. Discordant results were obtained by microscopy and PCR from six and three of the storm events, respectively, with multiple samples. Discordant microscopy or PCR results were also obtained among subsamples. Most of the 14 Cryptosporidium genotypes were found over a brief period. Cryptosporidium-positive samples had a mean of 1.9 genotypes per sample, with 39 of the 62 positive samples/subsamples having more than one genotype. Samples/subsamples with more than one genotype had an overall PCR-positive rate of 73%, compared to 34% for those with one genotype. The PCR amplification rate of samples was affected by the volume of DNA used in PCR.

Animals↗
PubMed2003

Sampling considerations for garden symphylans (Order: Cephalostigmata) in western Oregon.

Sampling recommendations were developed for a potato bait sampling method used to estimate garden symphylan (Scutigerella immaculata Newport) densities in western Oregon. Sample size requirements were developed using Taylor's power law to describe the relationship between sample means and variances. Developed sampling recommendations performed well at sample sizes of 30 and greater, when validated by resampling a cohort of 40 independent data sets. Sample size requirements for the bait sampling method were 1.5 times greater than the requirements for the soil sampling method over densities from 1 to 20 S. immaculata per sample unit. As S. immaculata densities increased from April to May, sample size requirements decreased by 36% for fixed precision levels. For sampling in April, decreasing the damage threshold from 20, to 10 and five S. immaculata per sample unit, required a 1.6 and 2.5 times greater sample size requirement, respectively, for a fixed precision level (c) appropriate for pest management (c = 0.25). The bait sampling method provides an efficient reliable alternative to the standard soil sampling method used to monitor garden symphylan populations.

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