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PubMed1997

Quality control of biomarker measurement in epidemiology.

The throughput and complexity of a biomarker assay will determine the amount of effort that can be expended on quality control and assurance. Clinical chemistry quality control procedures can be readily applied to simpler chemical analysis such as blood lead and cholesterol, but even complex cell-based biomarker techniques such as HPRT mutation analysis and cytogenetics benefit from a formal quality control approach. Collaborative interlaboratory exercises are essential, especially when no certified reference material is available, and these can play a central role in the control of laboratory drift. Recommendations are made for the quality control of biomarker measurement based on clinical chemistry techniques. These include recommendations for coding samples so that the laboratory scientist is unaware of exposure status and for the use of formal laboratory protocols.

Biomarkers, Tumor↗
PubMed2000

Measuring the epidemiology of distress: the rheumatology distress index.

OBJECTIVES: (1) To examine clinical and psychological variables to determine which are associated with psychologic and psychosocial severity or "distress"; (2) to investigate whether patients with the 2 major rheumatic disorders, rheumatoid arthritis (RA) and osteoarthritis (OA), differ in distress variables and distress; and (3) to develop and validate a simple, clinically acceptable index of distress suitable for routine care and research purposes. METHODS: A total of 2,403 patients were evaluated in 2 data sets (N = 1,399 and N = 1,490). The first data set was evaluated in the clinic by a routine clinical examination and administration of the Clinical Health Assessment Questionnaire (CLINHAQ). This instrument includes measures of pain, global severity, functional disability, anxiety, depression, sleep disturbance, fatigue, health satisfaction, and health status. The second data set was evaluated by a mailed questionnaire that included the CLINHAQ, but also coping scales, the Beliefs in Pain Control Questionnaire, the Self Performance Scale, and the Arthritis Helplessness Index. RESULTS: RA and OA groups had similar scores for the variables associated with distress: pain, global severity, functional disability, anxiety, depression, sleep disturbance, fatigue, health satisfaction, and health status. Patients with fibromyalgia (FM) had more abnormal scores for every variable, reflecting overall distress. Using patients with FM as a "gold standard" of distress, we developed an index in data set 2. the Rheumatology Distress Index (RDI), made up of 5 variables, anxiety, depression, global severity, fatigue, and sleep disturbance, that best identified patients with FM compared to other patients. We then validated the instrument on the distress severity clusters formed in data set 1. The correlation between RDI and distress severity cluster was 0.874 with all patients considered and 0.867 with FM patients excluded. In addition, RDI predicted 1,174 of 1,399 (83.9%) cluster memberships correctly. Compared with a battery of psychological and clinical tests that classified 74% of FM and non-FM patients correctly, the RDI and is only slightly less effective, classifying 70.3% correctly. CONCLUSION: Distress is a patient rather than a disease phenomenon. A simple, easy to administer self-report questionnaire can be used to classify patients according to their level of distress. The resulting index, the RDI. accurately identifies distressed and non-distressed patients. Such an index should be useful for patient care and research.

Aged↗
PubMed2002

Minor recurrent aphthous stomatitis and smoking: an epidemiological study measuring plasma cotinine.

OBJECTIVE: To compare blood cotinine levels between a group of patients with minor recurrent aphthous stomatitis (RAS) and a group representative of the general population, matched for age and gender. SETTING: Although smoking has been implicated as a protective factor in RAS, few studies have compared the prevalence of smoking in RAS patients with population controls. Cotinine is a smoking derivative with a long half-life in the circulation. Measurement of plasma cotinine levels provides an accurate and objective measurement of an individual's cigarette consumption. METHODS: Blood samples were taken from 84 RAS patients and 81 controls. A microplate enzyme immunoassay (EIA) was used to detect plasma cotinine levels. RESULTS: The number of RAS patients [2 (2.4%)] who were smokers (plasma cotinine > 25 microg ml(-1) was significantly lower than in the control group [12 (14.8%); P = 0.00102]. Furthermore, the mean cotinine level amongst smokers in the RAS group was significantly lower than in smokers in the control group (P = 0.0068). CONCLUSION: This study shows that a group of RAS patients is significantly less likely to contain smokers than a matched control population, and among smokers the level of cigarette use was significantly lower in RAS patients than the control population. The perceived negative association between RAS and smoking was supported by this epidemiological study.

Adult↗
PubMed2000

Implications of different fiber measures for epidemiologic studies of man-made vitreous fibers.

BACKGROUND: Several researchers have proposed fiber size ranges representing hypotheses about the biological activity of fibers. Each of these indices has a biologically plausible rationale, yet they propose different fiber dimensions. METHODS: Four biologically based and one standard fiber analytic method index, the NIOSH 7400 method with B rules, were evaluated in air monitoring data collected in a variety of fiber glass (FG) manufacturing settings to determine their impact on an assessment of fiber exposure for an epidemiologic study of the risk of respiratory cancer among FG production workers. RESULTS: All indices varied considerably within and among the range of fiber size distributions sampled in the FG factories. CONCLUSIONS: The asymptotic relative efficiencies (R(2)) calculated among the five indices indicate a potentially important loss of power from the use of the standard method index, if one of the biologically based indices is more closely related to the disease outcome in an epidemiologic study.

Epidemiologic Methods↗
PubMed2005

Estimation of prevalence and incidence based on occurrence of health-related events.

A new method for estimating incidence and prevalence is developed, which only requires observation of occurrence of health-related events within a given time window. Occurrence data are often easy to collect but estimating incidence and prevalence of a disease from such data is non-trivial, since the true disease status is not directly observed for all at the beginning of the study period. Our method for overcoming this problem is based on an idea first presented in 'The waiting time distribution as a graphical approach to epidemiologic measures of drug utilization' (Epidemiology 1997; 8:666-670). Their fundamental idea is to analyse the waiting time from start of the window to the first event of each individual, and we formalize this by establishing a parametric likelihood which allows ordinary maximum likelihood analysis and explicit modelling of censoring. The developed method is used to analyse incidence and prevalence of hypertension in a Danish cohort of 70+-year-olds. A simulation study on the finite sample properties of the method is reported, which indicates that the method gives a quite robust and cost-effective alternative to ordinary surveys and follow-up studies for estimating incidence and prevalence.

Aged↗
PubMedDate not supplied

[Problems of the use of the trend test as a dose-response measurement in epidemiology].

BACKGROUND: The objective of the dose-response analysis is to reveal the presence of a progressively response to an increased dose. One of the usual ways of doing so is the carrying out of the so-called trend test. However, the fact that this test may show statistical significance does not necessarily indicate that there is a uniform response between dose and response. This study aims to examine the various situations in which the use of the trend test is not always appropriate as well as given an overview of the use of potential alternatives. METHODS: Five theoretical dose-response scenarios have been created using for supposed case-control studies, in which the relationship was not always linear. The results-tables obtained have been analysed, leading to the attainment of the Chi-squared trent test, as well as the calculation of the linear component by means of the logistical regression. Subsequently, other alternative methods of trends analysis, such as categorical analysis, the transformation of the findings within the logistical model and the use of risk incrementals have been employed. RESULTS: The test of trends invariably proved to be significant, despite the fact that in four of the theoretical models there did not exist a clear relationship between dose and response. This significant result could lull its readers into proposing a linear dose-response relationship which, in fact, proves false. The alternative use of incremental risk models, or categorical analysis, permits the identification of situations in which there is no relationship. CONCLUSIONS: The trend test should only be employed in cases where the data demonstrates the existence of monotonous, lineal relationship that can be deduced from the results of categorical analysis, the use of incremental risk or the adjustment of various no linear models, although, in this cases, the significance of the test may bring forward no new information.

Case-Control Studies↗
PubMed1994

Malaria vaccine study site in Irian Jaya, Indonesia: Plasmodium falciparum incidence measurements and epidemiologic considerations in sample size estimation.

Malaria epidemiologic and entomologic studies were performed during both the high transmission and low transmission seasons to characterize the Plasmodium falciparum malaria transmission at a proposed malaria vaccine trial site in Irian Jaya, Indonesia. The study population consisted of two subsets: native Irianese men with lifelong exposure to malaria and transmigrants who arrived from a nonmalarious area 2.5 years before the start of the study. All subjects received a radical cure for malaria and were then monitored weekly by blood film. Both P. falciparum malaria attack rates and incidence densities were calculated; transmigrants had a significantly higher rate (P = 0.003) than the Irianese during the low transmission season study (20-weeks long) but not during the high transmission season study (12-weeks long). Lack of exposure-induced immunity left the transmigrants at a minimum 17-25% greater relative risk of becoming parasitemic compared with the Irianese during the low transmission season study. During the high transmission season study, 50% of the transmigrants were P. falciparum positive by week 6 and 50% of the Irianese by week 9. During the low transmission season, 50% of the transmigrants were positive by week 10 and 43% of the Irianese were positive by week 17. Entomologic studies showed that Anopheles koliensis was the predominant vector (> 98% of anopheline catch). Entomologic inoculation rates for P. falciparum were 0.018 and 0.39 infective bites/person/night for the low and high transmission seasons, respectively. New P. vivax cases represented between 16% and 42% of all initial malaria cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed2000

[Anthelmintic resistance in gastrointestinal Strongylidae in sheep and goats: new data on prevalence, epidemiology, preventive measures and alternatives to anthelmintic drugs].

Anthelmintic-resistant gastrointestinal nematodes represent the major problem in controlling of parasites of small ruminants in central Europe. This article gives a brief update on the prevalence of resistant populations in sheep and goat farms in Europe. New data on the selection and spread of anthelmintic resistance are reported and recommendations are given for minimising further increases in the incidence of resistant populations. New strategies which may play a role in integrated control programs in the future, e.g. vaccination and the development of nematode-resistant breeds of animals or of nematophagous fungi are briefly discussed.

Animals↗