Predicting reamputation risk in patients undergoing lower extremity amputation due to the complications of peripheral artery disease and/or diabetes

Background

Patients undergoing amputation of the lower extremity for the complications of peripheral artery disease and/or diabetes are at risk of treatment failure and the need for reamputation at a higher level. The aim of this study was to develop a patient-specific reamputation risk prediction model.

Methods

Patients with incident unilateral transmetatarsal, transtibial or transfemoral amputation between 2004 and 2014 secondary to diabetes and/or peripheral artery disease, and who survived 12 months after amputation, were identified using Veterans Health Administration databases. Procedure codes and natural language processing were used to define subsequent ipsilateral reamputation at the same or higher level. Stepdown logistic regression was used to develop the prediction model. It was then evaluated for calibration and discrimination by evaluating the goodness of fit, area under the receiver operating characteristic curve (AUC) and discrimination slope.

Results

Some 5260 patients were identified, of whom 1283 (24·4 per cent) underwent ipsilateral reamputation in the 12 months after initial amputation. Crude reamputation risks were 40·3, 25·9 and 9·7 per cent in the transmetatarsal, transtibial and transfemoral groups respectively. The final prediction model included 11 predictors (amputation level, sex, smoking, alcohol, rest pain, use of outpatient anticoagulants, diabetes, chronic obstructive pulmonary disease, white blood cell count, kidney failure and previous revascularization), along with four interaction terms. Evaluation of the prediction characteristics indicated good model calibration with goodness-of-fit testing, good discrimination (AUC 0·72) and a discrimination slope of 11·2 per cent.

Conclusion

A prediction model was developed to calculate individual risk of primary healing failure and the need for reamputation surgery at each amputation level. This model may assist clinical decision-making regarding amputation-level selection.

Mortality prediction following non-traumatic amputation of the lower extremity

BACKGROUND

Patients who undergo lower extremity amputation secondary to the complications of diabetes or peripheral artery disease have poor long-term survival. Providing patients and surgeons with individual-patient, rather than population, survival estimates provides them with important information to make individualized treatment decisions.

METHODS

Patients with peripheral artery disease and/or diabetes undergoing their first unilateral transmetatarsal, transtibial or transfemoral amputation were identified in the Veterans Affairs Surgical Quality Improvement Program (VASQIP) database. Stepdown logistic regression was used to develop a 1-year mortality risk prediction model from a list of 33 candidate predictors using data from three of five Department of Veterans Affairs national geographical regions. External geographical validation was performed using data from the remaining two regions. Calibration and discrimination were assessed in the development and validation samples.

RESULTS

The development sample included 5028 patients and the validation sample 2140. The final mortality prediction model (AMPREDICT-Mortality) included amputation level, age, BMI, race, functional status, congestive heart failure, dialysis, blood urea nitrogen level, and white blood cell and platelet counts. The model fit in the validation sample was good. The area under the receiver operating characteristic (ROC) curve for the validation sample was 0·76 and Cox calibration regression indicated excellent calibration (slope 0·96, 95 per cent c.i. 0·85 to 1·06; intercept 0·02, 95 per cent c.i. -0·12 to 0·17). Given the external validation characteristics, the development and validation samples were combined, giving a total sample of 7168.

CONCLUSION

The AMPREDICT-Mortality prediction model is a validated parsimonious model that can be used to inform the 1-year mortality risk following non-traumatic lower extremity amputation of patients with peripheral artery disease or diabetes.

Systematic reanalysis of genomic data improves quality of variant interpretation

As genomic sequencing expands, so does our knowledge of the link between genetic variation and disease. Deeper catalogs of variant frequencies improve identification of benign variants, while sequencing affected individuals reveals disease-associated variation. Accumulation of human genetic data thus makes reanalysis a means to maximize the benefits of clinical sequencing. We implemented pipelines to systematically reassess sequencing data from 494 individuals with developmental disability. Reanalysis yielded pathogenic or likely pathogenic (P/LP) variants that were not initially reported in 23 individuals, 6 described here, comprising a 16% increase in P/LP yield. We also downgraded 3 LP and 6 variants of uncertain significance (VUS) due to updated population frequency data. The likelihood of identifying a new P/LP variant increased over time, as ~22% of individuals who did not receive a P/LP variant at their original analysis subsequently did after 3 years. We show here that reanalysis and data sharing increase the diagnostic yield and accuracy of clinical sequencing.

Glycinergic signaling in the human nervous system: An overview of therapeutic drug targets and clinical effects

Glycine and related endogenous compounds (d-serine, d-alanine, sarcosine) serve critical roles in both excitatory and inhibitory neurotransmission and are influenced by a multitude of enzymes and transporters, including glycine transporter 1 and 2 (GlyT1 and GlyT2), d-amino acid oxidase (DAAO), serine racemase (SRR), alanine-serine-cysteine transporter 1 (Asc-1), and kynurenine aminotransferase (KAT). MEDLINE, Web of Science, and PsychINFO were searched for relevant human trials of compounds. Many studies utilizing exogenous administration of small molecule agonists of the glycineB site of n-methyl-d-aspartate receptor have been studied as have a growing number of glycine transporter type 1 (GlyT1) inhibitors. The clinical effects of these compounds are reviewed as are the potential effects of newer novel compounds.

Recent trends in testosterone testing, low testosterone levels, and testosterone treatment among Veterans

Low serum testosterone (T) is common and increasingly prevalent with increased age. Recent studies report an 'epidemic' of T prescribing and concern about unnecessary T treatment. We investigated the number of men tested for T, the prevalence of low serum T levels, and initiation of T treatment among those with low T levels in men treated at Veterans Affairs (VA) facilities in the Northwest US (VISN 20). We identified male Veterans aged 40-89 years and examined yearly proportions of men tested for T, found to have low T levels (total T < 280 ng/dL, free T < 34 pg/mL, or bioavailable T < 84 ng/dL), and subsequently treated with T from 2002 to 2011. We excluded men who had T treatment in the year prior and men with diagnoses of prostate or breast cancer. Treatment initiation was defined as the first prescription for T within a year following a low T test. From 2002 to 2011, the yearly population of eligible men in VISN 20 increased from 129 247 to 163 572. The proportion of men who had serum T tests increased from 3.2% in 2002 to 5.8% in 2011. Among the tested men, the percentage of men with low T levels increased from 35.0 to 47.3%. However, the proportion of men with low T levels who were given T treatment within a year decreased from 31.0 to 28.0%. Despite large increases in T testing, and detection of men with low T levels, there was a slight decrease in the proportion of men with low T levels who were treated with T. The decrease in T treatment during this time period contrasts with other studies and may be related to higher comorbidity in Veterans and/or VA formulary restrictions on the use of transdermal T formulations.

Weight loss intention, dietary behaviors, and barriers to dietary change in veterans with lower extremity amputations

BACKGROUND

Obesity is thought to be highly prevalent in persons with lower extremity amputations (LEAs) and can impair physical and social functioning.

OBJECTIVE

The aim of this study was to determine the prevalence of weight loss intention, weight loss strategies, dietary patterns, and barriers to making dietary changes, and their associations with body mass index (BMI, kg/m(2)), amputation characteristics, health status, and socioeconomic factors.

METHODS

We conducted a cross-sectional study (n = 150) using data from a self-administered questionnaire.

RESULTS

43% of participants were obese and 48% were trying to lose weight; 83% of those trying to lose weight reported trying to "eat differently", but only 7% were following a comprehensive weight loss program involving dietary changes, physical activity, and behavioral counseling. 21% of participants reported ≥ 6 barriers to changing their eating habits (e.g., habit, too little money, stress/depression). Obesity was associated with younger age, lower physical health scores, hypertension, arthritis, and diabetes. Compared to those not trying to lose weight, a greater proportion of those trying to lose weight had a BMI ≥ 35 kg/m(2), age <55 years, higher physical and mental health scores, and more frequent consumption of vegetables, beans, chicken, and fish.

CONCLUSIONS

Though over half of overweight and obese individuals with LEA were trying to lose weight, few reported following a comprehensive program to lose weight, which may indicate an unmet need for services for this group. To be effective, these programs will need to address the complex physical and mental health challenges that many of these individuals face.

Abundant and stable char residues in soils: implications for soil fertility and carbon sequestration

Large-scale soil application of biochar may enhance soil fertility, increasing crop production for the growing human population, while also sequestering atmospheric carbon. But reaching these beneficial outcomes requires an understanding of the relationships among biochar's structure, stability, and contribution to soil fertility. Using quantitative (13)C nuclear magnetic resonance (NMR) spectroscopy, we show that Terra Preta soils (fertile anthropogenic dark earths in Amazonia that were enriched with char >800 years ago) consist predominantly of char residues composed of ~6 fused aromatic rings substituted by COO(-) groups that significantly increase the soils' cation-exchange capacity and thus the retention of plant nutrients. We also show that highly productive, grassland-derived soils in the U.S. (Mollisols) contain char (generated by presettlement fires) that is structurally comparable to char in the Terra Preta soils and much more abundant than previously thought (~40-50% of organic C). Our findings indicate that these oxidized char residues represent a particularly stable, abundant, and fertility-enhancing form of soil organic matter.

Provincial differences in infant deaths in South Africa – an effect of antiretroviral interventions?

Original article

Lung function loss in relation to silica dust exposure in South African gold miners

OBJECTIVE

To estimate exposure-response relationships between respirable dust, respirable quartz and lung function loss in black South African gold miners.

METHODS

520 mineworkers aged >37 years were enrolled in a cross-sectional study. Gravimetric dust measurements were used to calculate cumulative respirable dust and quartz exposures. Excess lung function loss was defined as predicted minus observed forced expiratory volume in one second (FEV(1)) and forced vital capacity (FVC). The association between excess loss and exposure was estimated, adjusting for smoking, tuberculosis and silicosis.

RESULTS

Mean service length was 21.8 years, mean respirable dust 0.37 mg/m(3) and mean respirable quartz 0.053 mg/m(3). After adjustment, 1 mg-yr/m(3) increase in cumulative respirable dust exposure was associated with 18.7 ml mean excess loss in FVC [95% confidence interval (CI) 0.3, 37.1] and 16.2 ml in FEV1 (95% CI -0.3, 32.6). Mean excess loss with silicosis was 224.1 ml in FEV1 and 123.6 ml in FVC; with tuberculosis 347.4 ml in FEV1 and 264.3 ml in FVC.

CONCLUSION

Despite a healthy worker effect, lung function loss was demonstrable whether due to silicosis, tuberculosis or an independent effect of dust. A miner working at a respirable dust intensity of 0.37 mg/m(3) for 30 years would lose on average an additional 208 ml in FVC (95% CI 3, 412) in the absence of other disease, an impact greater than that of silicosis and comparable to that of tuberculosis. Improved dust control on the South African gold mines would reduce the risk of silicosis, tuberculosis and lung function impairment.

Tuberculosis and silica exposure in South African gold miners

AIMS

To examine the effect of silica exposure, in the absence of silicosis, on the prevalence of pulmonary tuberculosis (PTB), which is epidemic among South African gold miners.

METHODS

Cross-sectional study of 520 gold miners over 37 years of age. Length of service, and cumulative and average dust and quartz exposure indices were derived for each miner. Chest radiographs were read for PTB by two NIOSH "B" readers. PTB was defined as a self-reported history of PTB or PTB on chest radiograph. Logistic regression was used to adjust for age, smoking, and silicosis. PTB effects of different exposure metrics for silica, scaled on their interquartile range (IQR), were compared.

RESULTS

Means (ranges) were: age 46.7 (37.1-59.9) years; length of service 21.8 (6.3-34.5) years; average intensity of respirable quartz 0.053 (0-0.095) mg/m3. PTB prevalence was 19.4% (95% CI 16.0 to 22.8) on history alone, and 35.2% (95% CI 31.1 to 39.3) on history or on chest radiograph. Length of service was poorly predictive of PTB, while all exposure indices which included dust or quartz yielded prevalence odds ratios (PORs) of approximately 1.4 (95% CI approximately 1.1 to 1.8) for changes of one interquartile range in exposure. Controlling for silicosis--by adjustment or restriction--did not modify these results. Drillers and winch operators had the highest PTB prevalences and the highest dust and silica exposures.

CONCLUSION

Older in-service gold miners in South Africa have a high prevalence of PTB, which is significantly associated with dust and silica exposure, even in the absence of silicosis. Limitations include a survivor workforce and the use of cumulative exposures based on current exposures. Dust control is an important component in control of the PTB epidemic in South African gold mines.

Nuclear magnetic resonance and diffuse-reflectance infrared Fourier transform spectroscopy of biosolids-derived biocolloidal organic matter

We extracted the acid-soluble portion of municipal biosolids, fractionated it by both molecular weight (MW) and hydrophobicity, and used various solid-state nuclear magnetic resonance (NMR) methods and diffuse-reflectance infrared Fourier transform (DRIFT) spectroscopy to characterize the fractions. Spectroscopic characterization of the MW components of the biosolids-derived organic matter fractions revealed the presence of functionally distinct groups of compounds. Quantitative 13C NMR, CH spectral editing, and several two-dimensional NMR experiments show that the high-MW hydrophilic fraction in particular is structurally simple, consisting predominantly of N-acetylated polysaccharides, perhaps derived from bacterial peptidoglycans. In the high-MW hydrophobic fraction, aromatic compounds were present in addition to the N-acetylated polysaccharides. Infrared spectroscopy confirmed that hydrophilic fractions were dominated by carbohydrates and indicated that the lower-MW fractions lacked amide moieties. Complementary interpretations of the DRIFT and NMR spectra improved our knowledge of the components separated by this fractionation scheme, allowing better characterization of biosolids organic matter. Moreover, fractionation based on both MW and hydrophobicity may prove useful in detailed characterization of the structure of biosolids-derived organic matter and other similarly heterogeneous natural organic matter in soils and sediments.

Uptake of 18fluorodeoxyglucose in the cystic fibrosis lung: a measure of lung inflammation?

Positron emission tomography is a three-dimensional imaging technique that measures physiological effects, including metabolism. 18Fluorodeoxyglucose has been extensively used as a tracer of cellular energy metabolism in the brain and in tumour detection. As neutrophils utilise glucose as an energy source during their respiratory burst, it was hypothesised that 18fluorodeoxyglucose uptake, by these cells, could be interpreted as a measure of neutrophil activation in cystic fibrosis (CF). Ten adult CF patients were given a bolus intravenous injection of 18fluorodeoxyglucose, followed by a 90-min dynamic mid-lung acquisition scan. Right-lung 18fluorodeoxyglucose uptake was assessed using a Patlak plot and values were converted to glucose utilisation. Three clinically inactive pulmonary sarcoidosis patients served as controls. From the 10 CF patients with baseline sputum neutrophils of 14 x 10(6) cells x mL(-1) who were investigated, seven were found to have sputum at a normal or slightly depressed glucose utilisation rate (mean 1.33 micromol x g(-1) x h(-1)) compared with a mean of 2.82 micromol x g(-1) x h(-1) for the sarcoidosis patients. In eight patients, receiving inhaled tobramycin therapy, no change in lung glucose utilisation or sputum neutrophil counts were found. Despite high-sputum neutrophil levels, lung glucose utilisation was not elevated in patients with cystic fibrosis.

Correlation of poly(methylene)-rich amorphous aliphatic domains in humic substances with sorption of a nonpolar organic contaminant phenanthrene

The structural makeup of natural organic matter plays a major role in regulating its capacity to retain nonionic hydrophobic organic compounds (HOCs). We used a model HOC--phenanthrene--to investigate the correlations between sorption capacity, specifically the modified Freundlich coefficient (K'f), and compositional data of humic acids, humins, and a peat obtained from quantitative 13C solid-state NMR spectroscopy. A positive correlation between K'f and the weight fraction of amorphous poly(methylene) in the sorbents was observed. In contrast, the correlation between phenanthrene sorption capacity and aromaticity or polarity indices of the sorbents was insignificant. The nonpolar aliphatic carbon fraction, excluding poly(methylene), was only partially correlated with K'f. Detailed NMR analyses of the sorbents using 1H inversion-recovery experiments showed that 10-nm diameter domains of branched nonpolar aliphatic groups, which account for 20-50% of all nonpolar aliphatic segments and may be associated with the poly(methylene), were responsible for the partial correlation. The correlation between K'f and the amorphous nonpolar aliphatic domains including amorphous poly(methylene) was strong. The rubbery, relatively low-density, and amorphous nonpolar aliphatic domains can be expected to offer an excellent environment for the sorption of phenanthrene by partitioning. These observations suggest that the domains of amorphous poly(methylene) and branched nonpolar aliphatics, which make up 2-9 wt % of the organic fraction in our samples, may serve as good descriptors for the potential of natural organic matter to retain HOCs in the natural environments.

Test-retest reliability of an icon/calendar-based questionnaire used to assess occupational history

BACKGROUND

Self-reported work histories can be critical for both epidemiologic and clinical purposes. However, the complexity of some work histories, such as those of migrant farm workers, can hamper recall, resulting in inaccurate reporting. Memory aids may reduce such error. This study assesses the reliability of work histories collected using such aids in the form of an icon/calendar-based questionnaire.

METHODS

Thirty-one males engaged in farmwork and other manual labor for a median 28 years (range: 10-64) were interviewed twice, 8-14 months apart, about their lifetime employment. In each interview, subjects were asked about important life events, which were recorded with icons on a calendar. They were then asked to recount their work history, including for each job the tasks, crops or products handled, starting and ending dates, and location. This information was recorded, job-by-job, on the calendar with icons.

RESULTS

Interquestionnaire agreement of cumulative reported employment duration (as measured by the correlation coefficient) was moderate to high across all time periods for certain crops (e.g., r = 0.69-0.92 for apple-related work), by location (e.g., r = 0.76-0.95 for Washington State), and for agricultural work in general (r = 0.67-0.94), but was lower for specific tasks. Agreement of job counts was high for total work history for certain crops (e.g., r = 0.93 for apple-related work), by location (e.g., r = 0.90 for Washington State), and for agricultural work in general (r = 0.89), but paradoxically decreased with proximity to the interview date. Agreement of both measures tended to be highest for those tasks and crops in which subjects reported spending the most time. Categorization of subjects into tertiles on the basis of either cumulative duration or counts produced results similar to those observed for job counts.

CONCLUSIONS

The icon-calendar questionnaire is an effective tool for estimating cumulative duration of certain work categorizations among subjects with complex work histories.

Comparability of data obtained from migrant farmworkers and their spouses on occupational history

BACKGROUND

Epidemiologic studies, particularly case-control studies, often rely on proxy respondents to provide information about subjects' occupational histories. The quality of proxy-reported information in occupational histories has never been evaluated for migrant farmworkers.

METHODS

We compared occupational histories self-reported by 31 farmworkers with those reported by their wives. The work histories were obtained using an icon/calendar-based questionnaire that was designed to facilitate recall for migrant farmworkers, who typically have complex work histories.

RESULTS

The work histories provided by proxy respondents contained 32% fewer jobs and accounted for 24% fewer years than the self-reported histories. Correlations for lifetime duration of employment in different types of jobs were moderate to good for general agricultural jobs in Washington (0.70) and apple-related jobs (0.65), which were held by virtually all of the farmworkers; correlations were moderate to poor for less common jobs and for specific types of tasks. Agreement was better after marriage than before, and for jobs held in the current year compared to other time frames. Overall, the ability of the spouses to provide occupational histories for farmworkers was within the range observed in studies involving other occupations and industries.

CONCLUSIONS

In studies involving farmworkers, when study subjects cannot be interviewed, spouses can provide useful information on occupational histories. However, the information should be used only for more generalized exposure assessments; it is most appropriate for estimating cumulative duration of agricultural work, or recent work, by place or for common crops.

Sorption of phenanthrene by reference smectites

Fate and behavior of nonionic hydrophobic organic compounds (HOCs) in the environment is mainly controlled by their interactions with various components of soils and sediments. Due to their large surface area and abundance in many soils, smectites may greatly influence the fate and transport of HOCs in the environment. We used phenanthrene as a probe to explore the potential of reference smectites to sorb HOCs from aqueous solution. Batch experiments were used to construct phenanthrene sorption isotherms, and possible sorption mechanisms were inferred from the shape of the isotherms. Our results demonstrate that smectites can retain large amounts of phenanthrene from water. Phenanthrene sorption capacities of the reference smectites investigated in this study were comparable to those of soil clays containing a considerable amount of organic matter. Hectorite exhibited the highest sorption affinity and capacity followed by Panther Creek montmorillonite. The lack of correlation between Freundlich sorption constants (K'f) and indices of charge or hydrophobicity suggests that sorption of phenanthrene by smectites is primarily a physical phenomenon. Capillary condensation into a network of nanoor micropores created by quasicrystals is likely to be a dominant mechanism of phenanthrene retention by smectites.

Distribution and movement of sludge-derived trace metals in selected Nigerian soils

Use of metal-rich sewage sludge as soil fertilizer may result in trace- metal contamination of soils. This study was conducted to evaluate the effects of long-term sludge application on trace-metal (Zn, Cu, Pb, and Ni) distribution and potential bioavailability in Nigerian soils under a tropical wet-dry climate. Total metal analyses, sequential chemical fractionation, and DTPA extractions were carried out on samples of control and sludge-amended pedons in Nigeria (a Rhodic Kandiustult and two Rhodic Kandiustalfs from Nigeria, respectively). The sewage sludge applied to the soils contained higher levels of Zn and Cu than Pb and Ni. The control pedon contained low levels of all four metals. Soil enrichment factors (EF) were calculated for each metal in the sludge-amended pedons. Compared with the control soil, the sludge-amended pedons showed elevated levels of Zn and Cu, reflecting the trace-metal composition of the sewage sludge. Zinc and Cu in the sludge-amended soils were strongly enriched at all depths in the profile, indicating that they had moved below the zone of sludge application. The sequential extraction and DTPA analyses indicated that the sludge-amended soils contained more readily extractable and bioavailable metal ions than the unamended soil.

Neuropsychological test performance in a cognitively intact sample of older Japanese American adults

The purpose of this paper was to present population-based data showing the effects of age on cognitive test performance in a sample of older Japanese American adults. In addition, the relative effects of education, gender, and primary spoken language were compared to effects that have been reported in the literature for majority culture older adults. Subjects included 201 non-demented Japanese American adults age 70 and older currently enrolled in the Kame Project, a prospective study of aging and dementia in King County, WA. Cognitive tests included the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) neuropsychological assessment battery, WAIS-R Digit Span and Digit Symbol subtests, Trail Making Test, Purdue Pegboard, and Finger Tapping. Older age was associated with significantly (p<0.05) lower scores on all tests; less than high school education was associated with lower scores on all tests except Digit Span, Finger Tapping, and the Purdue Pegboard. Women and English-speaking participants scored higher than men and Japanese speakers on various tests of memory, attention, and visuomotor ability. These data reinforce the importance of using appropriately corrected norms when interpreting results of cognitive screening tests with minority culture older adults.

Porphyrins with exocyclic rings. 16. Synthesis and spectroscopic characterization of fluoranthoporphyrins, a new class of highly conjugated porphyrin chromophores

Porphyrins with fused aromatic rings are under detailed investigation due to their unique spectroscopic properties. To gain more insights into the effects due to ring annealation on the porphyrin chromophore, a series of fluoranthoporphyrins have been synthesized. Reaction of 3-nitrofluoranthene with isocyanoacetate esters in the presence of a phosphazene base afforded good yields of the fluorantho[2,3-c]pyrrole esters 8. Cleavage of the ester moiety with KOH in ethylene glycol afforded the parent heterocycle 9, and this condensed with 2 equiv of acetoxymethylpyrroles 10 in refluxing acetic acid-2-propanol to afford tripyrranes 11. Following cleavage of the tert-butyl ester protective groups with TFA, "3 + 1" condensation with pyrrole dialdehyde 12 gave the fluoranthoporphyrins 13 in good overall yields. In addition, reaction of tripyrrane 11 with acenaphthopyrrole dialdehyde 16 gave the mixed acenaphthofluoranthoporphyrin 17 in excellent yields. A difluoranthoporphyrin 18 was also prepared via a "2 + 2" MacDonald condensation. Reaction of fluoranthopyrrole 8a with dimethoxymethane in the presence of p-toluenesulfonic acid gave the symmetrical dipyrrylmethane 19, and following ester saponification, this was condensed with a dipyrrylmethane dialdehyde to afford the adj-difluoranthoporphyrin 18. The UV--vis spectra for these fluoranthoporphyrins gave a series of three broadened absorptions in the Soret band region, although the Q-bands were little effected by ring fusion. The nickel(II), copper(II), and zinc chelates were more unusual, showing strong absorptions near 600 nm. Difluoranthoporphyrin 18 showed many of the same spectroscopic features, although the presence of two ring fusions gave rise to an increase in the spectroscopic shifts. The mixed system 17 gave spectra that showed larger red shifts due to the acenaphthylene unit combined with the features due to the fluoranthene rings. This work further demonstrates the utility of aromatic ring fusion in altering the properties of porphyrinoid systems.

Utility of vibration sense testing for use in developing countries: comparison of extinction time on the tuning fork to vibration thresholds on the Vibratron II

The measurement of vibration sense loss is a useful tool to detect early impacts of neurotoxic chemicals. Measurement methods are needed for developing countries that are culturally unbiased, and which can be used under field conditions where electricity may be unavailable. Extinction time on a 256 Hz tuning fork was compared to vibration threshold measured on the Vibratron II for precision and agreement amongst 306 fruit farm workers as part of a study investigating neurobehavioural impacts of organophosphates in South Africa in 1993. Simultaneous data were also available from a 1 g accelerometer attached to the post of the Vibratron for comparisons. Precision of the tuning fork and Vibratron II appeared comparable and CVs (2.5 to 8.9%) were lower than that reported in the literature. Agreement of the tuning fork with the Vibratron was moderate (Spearmans correlation coefficient of the order of 0.39 to 0.42) whereas agreement between Vibratron and Accelerometer was high (Spearmans correlation of coefficient of the order of 0.78 to 0.83). Height, age and schooling were predictors of vibration sense for the Vibratron and accelerometer but only schooling for extinction time on the tuning fork. Height modified the variability of the Vibratron and accelerometer. Delays in application of the tuning fork to the base of the medial malleolus of 3 seconds or more were associated with average increases in extinction time of 1.7 s. The tuning fork, as standardised in this study, represents a relatively quick, easy and low-technology device with good utility, that is relatively resistant to the usual confounders for vibration threshold measurement. Further studies to explore its validity in relation to other well-recognised methods for detection of subtle neurotoxic impacts should be encouraged.

Medical care-seeking for menstrual symptoms

Fifty-six female undergraduates completed questionnaires regarding their menstrual symptoms, social learning experiences, and illness representations. The results showed that, compared to non-care-seekers, participants who had sought medical care for their menstrual symptoms reported more symptoms that had been problematic since menarche. Consistent with previous research, care-seekers reported more reinforcement for adolescent menstrual illness behaviours than non-care-seekers. Care-seekers also reported their symptoms as more serious and more difficult to ignore. The perceived seriousness and severity of symptoms were both correlated with reinforcement for adolescent menstrual symptoms. Lay referral was also a reported factor in care-seekers. The results of the present data are discussed with respect to previous research on care-seeking for menstrual and other symptoms.

Combining diagnostic test results to increase accuracy

When multiple diagnostic tests are performed on an individual or multiple disease markers are available it may be possible to combine the information to diagnose disease. We consider how to choose linear combinations of markers in order to optimize diagnostic accuracy. The accuracy index to be maximized is the area or partial area under the receiver operating characteristic (ROC) curve. We propose a distribution-free rank-based approach for optimizing the area under the ROC curve and compare it with logistic regression and with classic linear discriminant analysis (LDA). It has been shown that the latter method optimizes the area under the ROC curve when test results have a multivariate normal distribution for diseased and non-diseased populations. Simulation studies suggest that the proposed non-parametric method is efficient when data are multivariate normal.The distribution-free method is generalized to a smooth distribution-free approach to: (i) accommodate some reasonable smoothness assumptions; (ii) incorporate covariate effects; and (iii) yield optimized partial areas under the ROC curve. This latter feature is particularly important since it allows one to focus on a region of the ROC curve which is of most relevance to clinical practice. Neither logistic regression nor LDA necessarily maximize partial areas. The approaches are illustrated on two cancer datasets, one involving serum antigen markers for pancreatic cancer and the other involving longitudinal prostate specific antigen data.

Primary human immunodeficiency virus type 1 infection: clinical manifestations among women in Mombasa, Kenya

The occurrence of clinical manifestations associated with primary human immunodeficiency virus type 1 (HIV-1) infection was evaluated in a prospective cohort study of female sex workers in Mombasa, Kenya. Among 103 women who seroconverted to HIV-1, fever, vomiting, diarrhea, headache, arthralgia, myalgia, skin rash, swollen lymph nodes, extrainguinal lymphadenopathy, inguinal lymphadenopathy, and vaginal candidiasis were noted significantly more frequently at visits in which seroconversion first became evident. Eighty-one percent of seroconverting women had >/=1 of these 11 symptoms or signs. Among 44% of the women, the acute illness was severe enough to prevent them from working. Having >/=2 of 6 selected symptoms and signs yielded a sensitivity of 51%, specificity of 83%, positive likelihood ratio of 3.2, and negative likelihood ratio of 0.5 for acute HIV-1 infection. The recognition of primary HIV-1-infection illness in high-risk populations and subsequent risk-reduction counseling could potentially reduce secondary HIV-1 transmission during this highly infectious period.

The utility of apolipoprotein E genotyping in the diagnosis of Alzheimer disease in a community-based case series

CONTEXT

A recent collaborative study found that apolipoprotein E (APOE) genotype, in conjunction with the clinical diagnosis of Alzheimer disease (AD), was useful in improving diagnostic specificity (correctly not diagnosing AD) relative to the clinical diagnosis alone. Since these samples are particularly enriched with patients with AD and the APOE epsilon4 allele, results may not be generalizable to patients seen in the general medical community.

OBJECTIVE

To evaluate the diagnostic utility of the APOE genotype in diagnosing AD in a community-based case series from the largest health maintenance organization in an urban area.

DESIGN

We examined the effect of including APOE genotype on the diagnosis of AD in a community-based case series of patients presenting with memory complaints.

PATIENTS

Clinical and neuropathologic diagnoses and APOE genotype were obtained from 132 patients who underwent evaluation for dementia and subsequent autopsy.

MAIN OUTCOME MEASURES

Sensitivity, specificity, and positive and negative predictive values given various combinations of clinical diagnoses and the presence of an APOE epsilon4 allele.

RESULTS

Of the 132 patients, 94 had neuropathologically confirmed AD, yielding a prevalence of 71%. The clinical diagnosis alone yielded a sensitivity of 84%, an estimated specificity of 50%, and positive and negative predictive values of 81% and 56%, respectively. The presence of an epsilon4 allele alone was associated with an estimated sensitivity of 59%, specificity of 71%, and positive and negative predictive values of 83% and 41%, respectively. Using the presence of clinical AD and an epsilon4 allele decreased the sensitivity to 49% and increased the specificity to 84%. The positive and negative predictive values were 88% and 40%, respectively. Alternatively, the clinical diagnosis of AD or the presence of an epsilon4 allele in individuals not meeting clinical criteria for AD increases the estimated sensitivity to 94% but decreases the specificity to 37%. The positive and negative predictive values were 79% and 70%, respectively. The changes in the sensitivity and specificity for the combined tests relative to clinical diagnosis alone offset each other. For lower prevalence communities, the positive predictive value will be much lower than those observed herein.

CONCLUSIONS

Our findings do not support the use of APOE genotyping alone in the diagnosis of AD in the general medical community. Although the presence of an epsilon4 allele in older persons with clinical AD increased the probability of having AD and the absence of an epsilon4 allele in this group decreased the probability of having AD, the association is not strong enough in the differential diagnosis of non-Alzheimer dementia and AD.

Neuropsychological function in solvent-exposed South African paint makers

Neuropsychological and neurological function were investigated in 228 organic solvent exposed paint manufacturing workers in two factories. Solvent exposure was expressed as both American Conference of Governmental Industrial Hygienists 1990 Threshold Limit Value equivalents and total hydrocarbon parts per million. The World Health Organization (WHO) neurobehavioral core test battery, the Neurobehavioural Evaluation System--2 (NES-2), and the UNISA Neuropsychological Assessment Procedure (UNAP) were used to measure outcomes, and a Vibratron II was used to measure peripheral vibration sensation. Exposures were generally below the Threshold Limit Value, and no exposure effect was found. Possible explanations for this finding are discussed, including low exposure, exposure, and outcome misclassification, together with inappropriateness, nonvalidity, and relative insensitivity of neuropsychological tests. Only age predicted Vibratron score. Some tests were clearly inappropriate for use in developing countries. Neuropsychological tests were sensitive to educational level, age, alcohol consumption, and cultural indicators. The WHO tests in particular showed good construct validity for neuropsychological functions and should be more formally validated for use in developing countries. Nevertheless, a major problem of cultural dependence is evident for all neuropsychological tests used in this study, and methods for bypassing this problem in less developed settings are discussed.

Effect of circumcision on incidence of human immunodeficiency virus type 1 and other sexually transmitted diseases: a prospective cohort study of trucking company employees in Kenya

To determine the effect of circumcision status on acquisition of human immunodeficiency virus (HIV) type 1 and other sexually transmitted diseases, a prospective cohort study of 746 HIV-1-seronegative trucking company employees was conducted in Mombasa, Kenya. During the course of follow-up, 43 men acquired HIV-1 antibodies, yielding an annual incidence of 3.0%. The annual incidences of genital ulcers and urethritis were 4.2% and 15.5%, respectively. In multivariate analysis, after controlling for demographic and behavioral variables, uncircumcised status was an independent risk factor for HIV-1 infection (hazard rate ratio [HRR=4.0; 95% confidence interval [CI], 1.9-8.3) and genital ulcer disease (HRR=2.5; 95% CI, 1.1-5.3). Circumcision status had no effect on the acquisition of urethral infections and genital warts. In this prospective cohort of trucking company employees, uncircumcised status was associated with increased risk of HIV-1 infection and genital ulcer disease, and these effects remained after controlling for potential confounders.

A preliminary statistical examination of the effects of uncertainty and variability on environmental regulatory criteria for ozone

Basing the quantitative expression of environmental regulatory standards and associated compliance criteria on statistical principles has recently received attention in Europe, most visibly in a study by the UK Royal Commission on Environmental Pollution. These issues are timely for consideration in the USA, where a recent periodic review of National Ambient Air Quality Standards (NAAQS) has led to revision of the regulatory standards for ambient ozone and particulate matter. Salient statistical issues include accounting for errors of the first and second kind due to sampling and measurement error. These issues appear routine statistically and also may seem absent from regulations, but neither is necessarily the case. This paper is directed towards developing a methodology for examining the problem of dealing with uncertainty and variation in environmental regulations and compliance criteria. Our approach is illustrated through statistical analysis of the (old) 1 hour and the (new) 8 hour standards for ambient ozone, based on intensive monitoring in California's San Joaquin Valley during summer 1990 performed under the SARMAP Project. This paper presents preliminary findings based on quantifying measurement error or precision in terms of small-scale spatial and temporal variability, laying the groundwork for future work.

Cofactors for the acquisition of HIV-1 among heterosexual men: prospective cohort study of trucking company workers in Kenya

OBJECTIVE

To determine the prevalence, incidence, and correlates of HIV-1 infection in a cohort of east African trucking company employees.

METHODS

HIV-1-seronegative trucking company employees were enrolled in a prospective cohort study and evaluated at 3 monthly intervals for HIV-1 seroconversion, sexually transmitted diseases, and sexual behavior.

RESULTS

The baseline seroprevalence of HIV-1 among 1500 trucking company employees was 17.8%. Among 752 HIV-1-seronegative men who were followed, the HIV-1 annual seroincidence was 3.1%. In univariate analysis, HIV-1 acquisition was associated with age under 25 years, 10 years or less of sexual activity, occupation as a driver/driver's assistant, occupational travel for more than 14 days per month, religion other than Christian or Muslim, uncircumcised status, sex with a prostitute, sex with a girlfriend/casual partner, extramarital sex, and enrollment seropositivity to Treponema pallidum, Haemophilus ducreyi, and Herpes simplex virus type 2 (all P values < or = 0.05). Using multivariate analysis, HIV-1 acquisition was independently associated with 10 years or less of sexual activity (hazard rate ratio (HRR) 2.0, 95% confidence interval (CI) 1.0-4.3), occupation as a driver/driver's assistant (HRR 3.9, 95% CI 1.7-9.0), religion other than Christian or Muslim (HRR 6.1, 95% CI 1.4-25.7), uncircumcised status (HRR 2.3, 95% CI 1.0-5.0), and unprotected sex with a prostitute (HRR 2.8, 95% CI 1.1-7.0).

CONCLUSIONS

Trucking company employees had a high HIV-1 seroprevalence rate at enrollment and a high HIV-1 seroincidence during follow-up. Risk factors for HIV-1 seroconversion included years of sexual activity, occupation, religion, uncircumcised status, and unprotected sex with a prostitute. This population is an appropriate target for HIV-1 prevention trials and behavioral interventions.

Health status among farm workers in the Western Cape--collateral evidence from a study of occupational hazards

MOTIVATION

Farm workers are a marginalised occupational group whose poor living and working conditions may place them at increased risk for occupational and non-occupational morbidity and mortality. Research into the health status of farm workers has been neglected in the past.

AIMS AND OBJECTIVES

As part of an investigation into the neurological and neurobehavioural effects of exposure to organophosphate insecticides, this study describes the demographics, life histories, risk factors for chronic illness and selected indicators of general health status among a group of farm workers in the Western Cape.

STUDY DESIGN

Cross-sectional study conducted in the deciduous fruit farming industry in 1993.

SUBJECTS

164 pesticide applicators and 83 non-spraying controls (all men) from 73 farms, frequency matched for age and education.

MEASUREMENTS

A structured questionnaire, venous blood sample for serum and erythrocyte cholinesterase, albumin, gamma glutamyl transferase and haemoglobin assessment, height and weight measurement.

RESULTS

Most farm workers were children of farm workers and had lived and worked on farms for most of their lives. The study found substantial levels of illiteracy (21-44%, depending on the definition) and innumeracy (4%) and evidence of a significant morbidity burden: high levels of alcohol intake and ongoing reported application of the 'dop' system, high levels of head injury (70% of subjects) and evidence of substantial adult undernutrition. Protective equipment was relatively well distributed and used, although certain work activities (such as acting as a human marker) continue to pose substantial exposure hazards. There were no differences in respect of cholinesterase levels between spray applicators and controls, although past poisoning was reported by 9% of subjects.

CONCLUSION

Farm workers appear to be a closed community with a high disease burden. Their health needs pose substantial challenges to the public health authorities.

A model for the prediction of time to union in fractures of the tibia

BACKGROUND AND PURPOSE

This report covers the second arm of a trial, the main focus of which was to assess the effect of interferential currents (IFCs) on time to union in tibial fractures. No significant improvement was found with the use of IFCs for the parameters employed (Fourie & Bowerbank, 1997).

METHODS

The focus of this study is the development of logistic regression models which used subject characteristics to predict non-union of fracture within 24, 32 and 40 weeks. Such models could be used to identify clients for consideration of alternative interventions, for example, electric current stimulation, bone grafting or the injection of bone morphogenic proteins (BMPs). The usefulness of such models would depend on their ability to correctly identify subjects whose fractures do or do not unite. These models were validated with respect to their sensitivity and specificity to predict non-union for a separate data set.

RESULTS

The results indicated, for instance, that use of a model to predict non-union of fracture within 24 weeks would lead to 27% of subjects being correctly classified (as union or non-union), 51% of subjects whose fractures did not unite within 24 weeks were identified and 65% of subjects (diagnosed as non-union) whose fractures did not unite within 24 weeks (the closer these values are to 100% the more accurate the model).

CONCLUSIONS

The conclusion reached was that the models may have value for low-cost, non-invasive interventions, but that they could not be used to predict those cases where surgical involvement would be necessary, due to the high false-positive rate.

The usefulness of a weight gain spurt to identify women who will develop preeclampsia

OBJECTIVE

The usefulness of adaptive centiles for weight gain as well as sudden weight gain spurts in identifying women who will develop preeclampsia was assessed.

METHODS

A study sample of 99 women who developed preeclampsia and a control sample of 675 women with normal pregnancies, were randomly selected. Weight gain spurts were identified by the upper bound of adaptive maternal weight centiles. Average changes in weight between successive clinic visits were also assessed.

RESULTS

Weight gain exceeding the 90th percentile of the adaptive centiles resulted in estimated sensitivity and specificity of 52% and 66% and weight gain >0.9 kg per week between visits in 76% and 29% respectively. Of women who would develop preeclampsia identified by the adaptive chart, 62.0% exhibited abnormal weight gain prior to the onset of abnormal clinical findings.

CONCLUSIONS

A sudden weight gain spurt is a far from reliable sign of impending preeclampsia. This reason for weighing women at antenatal visits appears to be unfounded.

Prevalence odds ratio or prevalence ratio in the analysis of cross sectional data: what is to be done?

OBJECTIVES

To review the appropriateness of the prevalence odds ratio (POR) and the prevalence ratio (PR) as effect measures in the analysis of cross sectional data and to evaluate different models for the multivariate estimation of the PR.

METHODS

A system of linear differential equations corresponding to a dynamic model of a cohort with a chronic disease was developed. At any point in time, a cross sectional analysis of the people then in the cohort provided a prevalence based measure of the effect of exposure on disease. This formed the basis for exploring the relations between the POR, the PR, and the incidence rate ratio (IRR). Examples illustrate relations for various IRRs, prevalences, and differential exodus rates. Multivariate point and interval estimation of the PR by logistic regression is illustrated and compared with the results from proportional hazards regression (PH) and generalised linear modelling (GLM).

RESULTS

The POR is difficult to interpret without making restrictive assumptions and the POR and PR may lead to different conclusions with regard to confounding and effect modification. The PR is always conservative relative to the IRR and, if PR > 1, the POR is always > PR. In a fixed cohort and with an adverse exposure, the POR is always > or = IRR, but in a dynamic cohort with sufficient underlying follow up the POR may overestimate or underestimate the IRR, depending on the duration of follow up. Logistic regression models provide point and interval estimates of the PR (and POR) but may be intractable in the presence of many covariates. Proportional hazards and generalised linear models provide statistical methods directed specifically at the PR, but the interval estimation in the case of PH is conservative and the GLM procedure may require constrained estimation.

CONCLUSIONS

The PR is conservative, consistent, and interpretable relative to the IRR and should be used in preference to the POR. Multivariate estimation of the PR should be executed by means of generalised linear models or, conservatively, by proportional hazards regression.

Effects of long-term organophosphate exposures on neurological symptoms, vibration sense and tremor among South African farm workers

OBJECTIVES

This study assessed the relationship between long-term exposure to organophosphate insecticides and neurological symptoms, vibration sense, and motor tremor after control for the effect of past poisoning and acute exposure.

METHODS

This cross-sectional study included 164 pesticide applicators and 83 nonspraying reference workers on deciduous fruit farms. The workers were tested on the Vibratron II, on tests of dynamic and static tremor, and for a set of neurological and "dummy" symptoms. Exposure was derived with the use of a job-exposure matrix for pesticides in agriculture.

RESULTS

Compared with nonapplicators, current applicators reported significantly more dizziness, sleepiness, and headache and had a higher overall neurological symptom score. This association remained statistically significant after multiple logistic regression analyses controlling for a range of confounders and effect modifiers [odds ratio (OR) 2.25, for current applicators having high neurological score, 95% confidence interval (95% CI) 1.15-4.39]. The average lifetime intensity of organophosphate exposure was nonsignificantly associated with both neurological (OR 1.98, 95% CI 0.49-7.94) and "dummy" symptoms (OR 2.37, 95% CI 0.54-10.35). Previous pesticide poisoning was significantly associated with the neurological scores (OR 4.08, 95% CI 1.48-11.22) but not with the "dummy" symptoms. Vibration sense outcomes were associated with age and height, but not with the organophosphate exposure measures. In the multiple linear regression modeling for tremor intensity in the dominant hand, recent organophosphate exposure in the past 10 days was a significant predictor (partial correlation coefficient = 0.04), but none of the long-term organophosphate exposure measures were significant.

CONCLUSIONS

Strong evidence was found for an association between symptom outcomes and past organophosphate poisoning and between symptom outcomes and current spray activity. In contrast to symptoms, there was no association between either past poisoning or current spray activity and vibration sense or tremor outcome. Long-term organophosphate exposure did not appear to predict symptoms, vibration sense, or tremor outcome.

Meta-analysis and occupational epidemiology

Meta-analysis is increasingly appearing in the epidemiologic literature. Although originally performed in the context of experimental or randomized controlled study designs and with regard to problems that are amenable to these designs, the method has also been applied to studies in observational epidemiologic settings. This movement has generated considerable debate about the validity of meta-analysis in observational studies, which can be said to be rather shaky. Meta-analysis is also appearing in occupational epidemiology, and a recent application to studies of industrial cohorts exposed to organic solvents has illustrated many of the arguments against meta-analysis of observational study. The propensity of meta-analysis for disarming critical approaches to individual study methods such as the standardized morbidity or mortality ratio (SMR) as effect measure, and to application of commonly used biostatistical techniques is illustrated. A cautionary note is sounded.

Changes in corticomotor excitation and inhibition during prolonged submaximal muscle contractions

Changes in motor evoked potential (MEP) amplitude, post-MEP silent period duration, and interpolated twitch torque were measured using transcranial magnetic (TMS) and electrical (TES) stimulation during a 20% maximum voluntary contraction of the elbow flexors sustained to exhaustion. TMS- and TES-induced MEP amplitude increased progressively over the contraction period up until the point of exhaustion. The TMS-induced silent period was prolonged only during the second half of the contraction period, the time course being different from that of the MEP responses, whereas the TES-induced silent period did not change. The findings indicate that corticomotor excitability increases during a sustained submaximal voluntary contraction and that, as fatigue develops, there is a progressive buildup of intracortical inhibition. This may represent a mechanism whereby corticomotor output is maintained at an appropriate level to preserve optimal motor unit firing frequencies during a fatiguing contraction.

Characteristics of information resources preferred by primary care physicians

Primary care physicians use patient data, medical knowledge, logistic information, and population statistics. They rely on their personal knowledge to care for their patients, their top priority. When they seek information beyond this personal knowledge base, they frequently want information in the context of the care of a specific patient. They also continually add to their personal knowledge base. Less frequently, they seek logistic information and population statistics. For patient-specific questions, physicians most often seek medical facts or medical opinions. A physician may be persistent in seeking information if the patient's problem is perceived to be urgent and the doctor believes a definitive answer exists. Information resources for answering clinical questions should be readily available, familiar, and quick to use. Lifelong learning activities should also be readily available, and they should require a minimum of time, effort, and expense. Minimal cost in time and effort is particularly important when knowledge is sought as a part of ongoing medical learning, since there is less immediate benefit to balance the time and effort invested in information seeking.

Predictive value of conditional centile charts for weight and fundal height in pregnancy in detecting light for gestational age births

OBJECTIVE

To estimate the predictive value of weight and symphysis fundal height (SFH) in pregnancy to detect light for gestational age (LiGA) births.

STUDY DESIGN

New conditional centile charts for longitudinal monitoring of maternal weight and fundal height in pregnancy were developed based on the records of 676 women with singleton pregnancies and no complications. The records of these women and of a further sample of 102 women who had LiGA deliveries were used to assess the sensitivity and specificity of the charts in detecting LiGA during pregnancy.

RESULTS

Maternal weight is a poor predictor of LiGA births. Fundal height shows moderate predictive ability. The simple cross-sectional chart for fundal height at the 20th percentile cutoff has sensitivity and specificity of 66% in detecting LiGA births.

CONCLUSIONS

Monitoring via a cross-sectional chart of fundal height offers a potentially useful screening method. The results of this study add support to arguments that routine weighing in pregnancy should be abandoned.

Construction of multivariate centile charts for longitudinal measurements

Reference centiles are commonly used as a means of identifying whether some measure of interest on an individual lies within a 'normal' range. Individuals outside the range may be at risk for some problem outcome. The information needed to screen for problem outcomes in often multivariate in nature. We develop a multivariate approach to centile estimation which allows for updating of centiles based on the prior path of the individuals as well as adjustments to the centiles according to individual covariate values. It is also possible to consider several variables jointly as a screen for problem outcomes.

Corticomotor representation of the sternocleidomastoid muscle

The topography of the cortical motor projection to the sternocleidomastoid (SCM) muscles was investigated in 15 normal subjects using the technique of transcranial magnetic stimulation. Contrary to the long-held view that the representation of the neck muscles in the motor strip is close to that of the face, our findings indicate that the projection to both the ipsilateral and contralateral SCM muscles arises from an area of cortex high up on the cerebral convexity close to the trunk representation and at a comparable level to the sensory representation of the neck in the post-central cortex. The use of shielded intramuscular recordings showed that surface recordings detect activity not only from the SCM muscle but also from the overlying platysma muscle whose cortical representation is lateral to that of the hand muscles. Our findings confirm that the corticomotor projection to the SCM muscle follows both a contralateral monosynaptic pathway, and an ipsilateral pathway, and indicate that the latter pathway may be disynaptic.

The use (and abuse) of reference centiles with an application to weight gain in pregnancy

Centile charts are commonly used in many areas of health research and practice, e.g. growth charts for children, Doppler ultrasonography in pregnancy and assessment of cholesterol levels at different ages. Yet there are a number of aspects of both their construction and application that are problematic and it is some of these issues that will be raised in this paper. The objective of the paper is to outline, in a non-technical way, some of the issues that need to be considered by the practitioner in estimating and using reference centile charts, but which frequently are either not known or ignored. These include: (i) the choice of reference population; (ii) how to estimate centiles; (iii) formally incorporating previous measurements on an individual, e.g. the interpretation of a child's weight that is on the 50th percentile for its age will be different if it has been moving along the 90th percentile at previous ages than if it has consistently been on the 50th percentile; and (iv) evaluation of centile charts used as a screen for problems. The concepts are introduced using an aspect of a study conducted at Tygerberg Hospital where centile charts for maternal weight gain in pregnancy were developed and assessed for their usefulness in detecting light-for-gestational-age (LiGA) births. The reference centile charts for maternal weight show poor discriminating ability between LiGA and normal births. These results support arguments in favour of abandoning the routine weighing of pregnant women.

An investigation into neurologic and neurobehavioral effects of long-term agrichemical use among deciduous fruit farm workers in the Western Cape, South Africa

Long-term exposure to organophosphates (OPs) in the absence of acute poisoning is increasingly suspected of causing chronic neurologic and neurobehavioral effects. A cross-sectional survey of 163 spray operators on deciduous fruit farms in the Western Cape, South Africa, and 84 nonspraying labororers was conducted in 1993 to investigate the relationship between long-term OP exposures and neurological and neurobehavioral outcomes. The study also sought to evaluate the performance of a set of neurobehavioral test batteries based on the information-processing theory of cognitive psychology, relative to the more established World Health Organization's Neurobehavioral Core Test Battery (WHO NCTB). These information-processing tests were designed for use in studies of subjects with little education, which are frequently conducted in developing countries in agriculture. They draw on experience from a previous South African study in which problems were encountered with a lack of cross-cultural validity of conventional test batteries. No evidence was found of a relationship between long-term OP exposure and loss of vibration sense. Small associations were found with the NCTB Pursuit-Aiming and Santa Ana (nondominant hand) subtests. The overall evidence of neurologic and neurobehavioral effects of long-term OP exposure was small; exposure misclassification may have contributed to this finding. Important confounders such as brain injury, alcohol consumption, and nutritional status were identified.

A centile chart for birth weight for an urban population of the Western Cape

Evidence from large epidemiological studies has supported concern that being born light for gestational age (LiGA) may be detrimental. The incidence of LiGA babies is an important indicator of the health of women of reproductive age in deprived communities. In the assessment of LiGA in the Western Cape, centile charts constructed for populations in other parts of the world are generally used. These charts, however, may not be appropriate. Patients residing in the area served by the Tygerberg Hospital obstetric service, who booked early with singleton pregnancies, had their gestational age confirmed by early ultrasound and delivered between 1 March 1989 and 28 February 1990 were included in the study. The sample consisted of 3,643 patients. The mean birth weight was 2,995 g (SD 573 g) and the range 760-5,080 g. The distribution of birth weight at each week of gestation from 28 to 42 weeks was not normal. The 4-parameter Johnson family of densities was used to model the distribution of birth weight at each gestational age. A comparison of the distribution of birth weight in the study relative to the perinatal growth chart for international reference constructed by Dunn was also made. In addition to considering an overall chart, the sample was subdivided according to a number of characteristics (e.g. gender, firstborn and latter-born babies, smoking habit, hypertensive disorders and induction of labour) in order to explore their impact on the distribution of birth weight. Having explored the potential impact of all these factors, it was concluded that a single chart including all patients could be constructed.

Information-seeking coping and anxiety in school-age children anticipating surgery

This study examined the relation between coping behavior and anxiety among school-age children anticipating an elective tonsillectomy and/or adenoidectomy. The demographic variables of age, gender, previous hospitalization, and birth order were also studied in relation to both coping and anxiety. Interview methods were utilized to measure information-seeking and information-limiting coping behaviors and feelings of anxiety. The results of this study indicate that children who used primarily information-seeking or information-limiting strategies were successful (as measured by low anxiety levels) in managing the stress of anticipated hospitalization. Children using information-seeking strategies for some, but not all, aspects of the hospitalization experience reported the greatest anxiety. The demographic variables were not related to either anxiety or coping.

Repeatability and validity of a field kit for estimation of cholinesterase in whole blood

OBJECTIVES

To evaluate a spectrophotometric field kit (Test-Mate-OP) for repeatability and validity in comparison with reference laboratory methods and to model its anticipated sensitivity and specificity based on these findings.

METHODS

76 farm workers between the age of 20 and 55, of whom 30 were pesticide applicators exposed to a range of organophosphates in the preceding 10 days, had blood taken for plasma cholinesterase (PCE) and erythrocyte cholinesterase (ECE) measurement by field kit or laboratory methods. Paired blinded duplicate samples were taken from subgroups in the sample to assess repeatability of laboratory and field kit methods. Field kits were also used to test venous blood in one subgroup. The variance obtained for the field kit tests was then applied to two hypothetical scenarios that used published action guidelines to model the kit's sensitivity and specificity.

RESULTS

Repeatability for PCE was much poorer and for ECE slightly poorer than that of laboratory measures. A substantial upward bias for field kit ECE relative to laboratory measurements was found. Sensitivity of the kit to a 40% drop in PCE was 67%, whereas that for ECE was 89%. Specificity of the kit with no change in mean of the population was 100% for ECE and 91% for PCE.

CONCLUSION

Field kit ECE estimation seems to be sufficiently repeatable for surveillance activities, whereas PCE does not. Repeatability of both tests seems to be too low for use in epidemiological dose-response investigations. Further research is indicated to characterise the upward bias in ECE estimation on the kit.

Effect of chronic DDC treatment on LHRH and substance P amidation processes in the rat

We examined the effects of chronic diethyldithiocarbamate (DDC) treatment on the concentrations of methionine-enkephalin, mature and unamidated forms (-Gly) of luteinizing hormone releasing hormone (LHRH) and substance P (SP) in various regions of the central nervous system (CNS). Chronic DDC treatment resulted in elevations of LHRH-Gly like immunoreactivity in the preoptic area (POA) and the medial basal hypothalamus (MBH), as well as elevations in SP-Gly like immunoreactivity in all areas of the CNS examined. Castration altered the ratios of SP-G-like/SP-like immunoreactivity in the pons, and LHRH-Gly like immunoreactivity in the MBH. Met-enkephalin concentrations were significantly elevated in the pons and medulla of intact DDC-treated animals, and in the POA of both intact- and castrated DDC-treated animals. Results demonstrate that it is possible to detect basal levels of unamidated LHRH and SP in many areas of the CNS, with ratios of unamidated/amidated peptides representing a unique and sensitive method for determining altered posttranslational processing of these transmitters, especially under altered endocrine states such as castration. Pharmacological blockade of terminal enzymatic processing of these peptides may be useful in studying upstream regulatory events in peptidergic neurons.

A role for the ecological study in the developing world

Retrospective case-control or prospective (follow-up) studies are important epidemiological tools and have provided useful information on exposure disease associations. Prospective studies would be the ideal option, but many countries (particularly in the developing world) do not have the necessary infrastructure to follow people up. Both retrospective and prospective studies are, however, sometimes conducted without due regard for their own limitations. These limitations are exacerbated when measures of exposure or disease are based on a single measurement and where the population under study is homogeneous with regard to exposure. The former is responsible for regression dilution bias and the latter for a lack of contrasts between exposure groups. Both factors would attenuate any relationship between exposure and disease. Ecological studies in epidemiology are weaker in design than case-control or prospective studies, but in some circumstances an ecological approach, which looks at the prevalence of an exposure or disorder in a number of areas of varying disease rates, may offer some advantages.