Biomedical subjects

Agus Salim

Publications and source records attributed to Agus Salim.

7 recordsLinked to original sources

PubMed2007

An analysis for a cross-over cohort study with an application to the study of triggers of Menière's disease.

When studying the effect of a transient exposure on the risk of a rare illness, for time and cost effectiveness it is desirable to follow a cohort of individuals who are 'prone' to the illness over an observation period. In this paper, we present a method of analysis for data arising from such a study. The proposed method can be used to estimate the relative risk of an exposure triggering the illness and the distribution of the time delay from exposure to the onset of illness. The model is extended to include covariate effects and to the situation where there are two types of exposure. For the two types of exposures situation, a model to handle a possible synergism of the exposures is proposed. Finally, the method is applied to study the potential triggers of attacks of Menière's disease.

Acute Disease↗

PubMed2006

Air travel and the risk of deep vein thrombosis.

BACKGROUND: The magnitude of the risk of venous thromboembolism (VTE) following air travel has been difficult to resolve due to a lack of adequate data. We determine the association more precisely by using a large dataset and an improved method of analysis. METHOD: Data on air-travel history for each of 5,196 patients hospitalised for VTE in Western Australia from 1981 to 1999 is analysed using a log-linear regression model for the probability that a flight triggers VTE and for the baseline hazard rate for VTE hospitalisation. RESULTS: The risk of VTE being triggered on the day of an international flight relative to a flight-free day is 29.8 (95% CI 22.4-37.3). Evidence that this relative risk depends on age is weak (p = 0.06), but the absolute risk clearly depends on age. The annual relative risk for an individual taking one international flight, compared with an individual of the same age taking no flight, is estimated to be 1.079. The estimated median time from flight to hospital admission is 4.7 days (95% CI 3.8-5.6) and the estimated 95th percentile is 13.3 (95% CI 10.3-16.8). CONCLUSIONS: Evidence for an association between international air travel and VTE hospitalisation is strong and passengers should be advised on ways to minimise risk during long flights. While 29.8 is a large relative risk, it must be remembered that the baseline risk is very small and the relative risk applies only to the unobserved triggering of a deep vein thrombosis episode on the day of travel; the consequent hospitalisation occurs on one of numerous ensuing days.

Aviation↗

PubMed2005

Accommodation of additional non-randomly sampled cases in a study of Helicobacter pylori infection in families.

Epidemiological studies with two-stage designs typically gather information about some covariates from all study subjects in the first sampling stage, while additional data from only a subset of the subjects are collected in the second sampling stage. Appropriate analysis of two-stage studies maintains validity and can also improve precision. We describe an application of a weighted likelihood method, mean-score logistic regression, to accommodate data from a cross-sectional study of Helicobacter pylori infection in children, where the study sample was enriched with additional non-randomly sampled cases. The present work exemplifies how careful analysis of epidemiological data from complex sampling schemes can adjust for potential selection bias, improve precision and enable a more complete investigation of factors of interest. Our results highlight the importance of H. pylori infected mothers and siblings as risk factors for the infection in children in Sweden.

Child↗

PubMed2005

Analysis of a potential trigger of an acute illness.

Sometimes certain short-term risk exposures are postulated to act as a trigger for the onset of a specific acute illness. When the incidence of the illness is low it is desirable to investigate this possible association using only data on cases detected during a specific observation period. Here we propose an analysis for such a study based on a model expressed in terms of the probability that the exposure triggers the illness and a random delay from a triggered illness until its diagnosis. Both the natural hazard rate for the illness and the probability that the exposure triggers the illness are assumed to be small and possibly dependent on age and covariates such as sex and duration or severity of the exposure. The method of analysis is illustrated with a study of the association between long flights and hospitalization for venous thromboembolism.

Acute Disease↗

PubMed2004

Modelling infectious disease transmission with complex exposure pattern and sparse outcome data.

We present a regression modelling framework to analyse infectious disease transmission during a time period where extensive exposure data are available, but where the outcome data are sparse. A latent variable model is used for each exposure time, allowing a straight-forward accumulation of risk for a collection of exposures for which outcome data are available. We describe an analysis of HIV infection from blood products among a cohort of haemophiliacs in Ireland between 1980 and 1985. The analysis provides estimates of the time pattern and batch effects; we show how analytical complexity such as smoothly varying coefficients or random coefficient models can be accommodated by the model. Finally, we discuss other problems where the model is applicable.

Cohort Studies↗

PubMed2004

QT dispersion, QT maximum and risk of cardiac death in the Caerphilly Heart Study.

BACKGROUND: It has been postulated that increased inter-lead differences in QT interval (QT dispersion) and the maximum QT interval (QTmax), in the standard 12-lead electrocardiogram (ECG), may be associated with an increased risk of cardiac death. The aims of this study were to assess the relationship between QT dispersion and QTmax, corrected and uncorrected for heart rate, and the risk of cardiac death. DESIGN: Nested case-control study within the Caerphilly prospective cohort study. METHODS: We studied 2512 men who participated in phase 1 of the Caerphilly study between 1979 and 1983. After a mean follow up of 7.1 years, 218 men had died from coronary heart disease and these men were compared with 218 age-matched controls. RESULTS: Data are presented on 422 patients with ECG suitable for analysis, 207 cases and 215 controls. Four trained observers measured the QT intervals and the reliability of each observer was estimated using repeat measurements on a randomly chosen sub-sample of ECGs. Median corrected QT dispersion and corrected QTmax were significantly higher in cases than in controls (51.9 versus 47.7 ms [P=0.01] and 430 versus 421 ms [P<0.001] respectively). In univariate analyses by quartiles of corrected QT dispersion and corrected QTmax, increased risk was largely confined to the upper quartile of the distribution with these subjects having twice the risk of those in the lower quartile [odds ratio (OR) 2.14, 95% confidence interval (CI) 1.2-3.7 and 2.56 (95% CI 1.5-4.5) respectively]. In logistic regression analysis, adjusted for age, smoking, body mass index, hypertension, history of myocardial infarction and ECG Minnesota code, we observed an increased risk in the upper quartile of the corrected QT dispersion relative to the other three quartiles combined [adjusted OR=1.74 (P=0.03)]. The magnitude of this association was increased in analyses based on the data from the most reliable observers. The association between corrected QTmax and cardiac death was attenuated in multivariate analysis. The findings in relation to both uncorrected QT dispersion and uncorrected QTmax were similar, i.e., consistent with a significant independent effect of QT dispersion but not QTmax for cardiac death in multivariate analysis. CONCLUSION: The data suggest that QT dispersion is an independent predictor of cardiac death provided it can be measured with sufficient reliability. The association is non-linear with increased risk largely confined to the upper quartile of the distribution. The QT maximum is not an independent predictor of cardiac death.

Body Mass Index↗

PubMed2004

Temporal variation in Irish suicide rates.

Using Irish suicide data for the period 1990-1998, the independent effects of month and day adjusting for age, gender, and calendar year effects and distinguishing between holiday and working Mondays were assessed. The male suicide rate was significantly higher on working Mondays (+31%) and Saturdays (+14%), and during April, June, and August (+17%), after adjustment for the other variables. In contrast, female suicide rates were higher only in August (+35%) and exhibited no day effect. Teenage men had a greater elevation of risk on Saturdays, Sundays, and both working and holiday Mondays than any other group. The study findings should be taken into account in the planning of specialized health care services and helplines for suicidal people. Furthermore, the findings provide support for Gabennesch's (1988) broken promise theory and the relationship between dysfunctions of the serotonergic system and suicidal behavior.

Adolescent↗