Presentation on theme: "American Journal of Epidemiology Impact factor: 5.745 5-Yr impact factor: 6.105 Current Issue (Volume 175 Issue 5 March 1, 2012)"— Presentation transcript:
American Journal of Epidemiology Impact factor: 5.745 5-Yr impact factor: 6.105 Current Issue (Volume 175 Issue 5 March 1, 2012)
Abstract 1 of 13CommentaryAbstract 1 of 13 Influenza and Community-acquired Pneumonia Interactions: The Impact of Order and Time of Infection on Population Patterns Discoveries made during the 1918 influenza A pandemic and reports of severe disease associated with coinfection during the 2009 hemagglutinin type 1 and neuraminidase type 1 (commonly known as H1N1 or swine flu) pandemic have renewed interest in the role of coinfection in disease pathogenesis. The authors assessed how various timings of coinfection with influenza virus and pneumonia-causing bacteria could affect the severity of illness at multiple levels of interaction, including the biologic and population levels. Animal studies most strongly support a single pathway of coinfection with influenza inoculation occurring approximately 7 days before inoculation with Streptococcus pneumoniae, but less-examined pathways of infection also may be important for human disease. The authors discussed the implications of each pathway for disease prevention and what they would expect to see at the population level if there were sufficient data available. Lastly, the authors identified crucial gaps in the study of timing of coinfection and proposed related research questions.
Abstract 2 of 13PRACTICE OF EPIDEMIOLOGYAbstract 2 of 13 Bayesian Posterior Distributions Without Markov Chains Bayesian posterior parameter distributions are often simulated using Markov chain Monte Carlo (MCMC) methods. However, MCMC methods are not always necessary and do not help the uninitiated understand Bayesian inference. As a bridge to understanding Bayesian inference, the authors illustrate a transparent rejection sampling method. In example 1, they illustrate rejection sampling using 36 cases and 198 controls from a case-control study (1976–1983) assessing the relation between residential exposure to magnetic fields and the development of childhood cancer. Results from rejection sampling (odds ratio (OR) = 1.69, 95% posterior interval (PI): 0.57, 5.00) were similar to MCMC results (OR = 1.69, 95% PI: 0.58, 4.95) and approximations from data-augmentation priors (OR = 1.74, 95% PI: 0.60, 5.06). In example 2, the authors apply rejection sampling to a cohort study of 315 human immunodeficiency virus seroconverters (1984– 1998) to assess the relation between viral load after infection and 5-year incidence of acquired immunodeficiency syndrome, adjusting for (continuous) age at seroconversion and race. In this more complex example, rejection sampling required a notably longer run time than MCMC sampling but remained feasible and again yielded similar results. The transparency of the proposed approach comes at a price of being less broadly applicable than MCMC.
Abstract 3 of 13PRACTICE OF EPIDEMIOLOGY Invited CommentaryAbstract 3 of 13 Invited Commentary: Lost in Estimation—Searching for Alternatives to Markov Chains to Fit Complex Bayesian Models Bayesian methods have seen an increase in popularity in a wide variety of scientific fields, including epidemiology. One of the main reasons for their widespread application is the power of the Markov chain Monte Carlo (MCMC) techniques generally used to fit these models. As a result, researchers often implicitly associate Bayesian models with MCMC estimation procedures. However, Bayesian models do not always require Markov-chain-based methods for parameter estimation. This is important, as MCMC estimation methods, while generally quite powerful, are complex and computationally expensive and suffer from convergence problems related to the manner in which they generate correlated samples used to estimate probability distributions for parameters of interest. In this issue of the Journal, Cole et al. (Am J Epidemiol. 2012;175(5):368–375) present an interesting paper that discusses non-Markov-chain-based approaches to fitting Bayesian models. These methods, though limited, can overcome some of the problems associated with MCMC techniques and promise to provide simpler approaches to fitting Bayesian models. Applied researchers will find these estimation approaches intuitively appealing and will gain a deeper understanding of Bayesian models through their use. However, readers should be aware that other non-Markov-chain- based methods are currently in active development and have been widely published in other fields.
Abstract 5 of 13PRACTICE OF EPIDEMIOLOGYAbstract 5 of 13 Marginal Structural Models for Case-Cohort Study Designs to Estimate the Association of Antiretroviral Therapy Initiation With Incident AIDS or Death To estimate the association of antiretroviral therapy initiation with incident acquired immunodeficiency syndrome (AIDS) or death while accounting for time-varying confounding in a cost-efficient manner, the authors combined a case-cohort study design with inverse probability-weighted estimation of a marginal structural Cox proportional hazards model. A total of 950 adults who were positive for human immunodeficiency virus type 1 were followed in 2 US cohort studies between 1995 and 2007. In the full cohort, 211 AIDS cases or deaths occurred during 4,456 person-years. In an illustrative 20% random subcohort of 190 participants, 41 AIDS cases or deaths occurred during 861 person-years. Accounting for measured confounders and determinants of dropout by inverse probability weighting, the full cohort hazard ratio was 0.41 (95% confidence interval: 0.26, 0.65) and the case-cohort hazard ratio was 0.47 (95% confidence interval: 0.26, 0.83). Standard multivariable-adjusted hazard ratios were closer to the null, regardless of study design. The precision lost with the case-cohort design was modest given the cost savings. Results from Monte Carlo simulations demonstrated that the proposed approach yields approximately unbiased estimates of the hazard ratio with appropriate confidence interval coverage. Marginal structural model analysis of case-cohort study designs provides a cost-efficient design coupled with an accurate analytic method for research settings in which there is time-varying confounding.
Abstract 6 of 13PRACTICE OF EPIDEMIOLOGYAbstract 6 of 13 Racial/Ethnic Differences in Responses to the Everyday Discrimination Scale: A Differential Item Functioning Analysis The authors examined the impact of race/ethnicity on responses to the Everyday Discrimination Scale, one of the most widely used discrimination scales in epidemiologic and public health research. Participants were 3,295 middle-aged US women (African-American, Caucasian, Chinese, Hispanic, and Japanese) from the Study of Women’s Health Across the Nation (SWAN) baseline examination (1996– 1997). Multiple-indicator, multiple-cause models were used to examine differential item functioning (DIF) on the Everyday Discrimination Scale by race/ethnicity. After adjustment for age, education, and language of interview, meaningful DIF was observed for 3 (out of 10) items: “receiving poorer service in restaurants or stores,” “being treated as if you are dishonest,” and “being treated with less courtesy than other people” (all P's < 0.001). Consequently, the “profile” of everyday discrimination differed slightly for women of different racial/ethnic groups, with certain “public” experiences appearing to have more salience for African-American and Chinese women and “dishonesty” having more salience for racial/ethnic minority women overall. “Courtesy” appeared to have more salience for Hispanic women only in comparison with African-American women. Findings suggest that the Everyday Discrimination Scale could potentially be used across racial/ethnic groups as originally intended. However, researchers should use caution with items that demonstrated DIF.
Abstract 7 of 13Original ContributionAbstract 7 of 13 Smoking and Risk of Incident Psoriasis Among Women and Men in the United States: A Combined Analysis The authors evaluated the association between smoking and the incidence of psoriasis among 185,836 participants from a cohort of older women (the Nurses’ Health Study, 1996–2008), a cohort of younger women (the Nurses’ Health Study II, 1991–2005), and a cohort of men (Health Professionals’ Follow-up Study, 1986–2006). Information on smoking was collected biennially during follow-up. The authors identified a total of 2,410 participants with incident psoriasis. Compared with never smokers, past smokers had a relative risk of incident psoriasis of 1.39 (95% confidence interval (CI): 1.27, 1.52) and current smokers had a relative risk of 1.94 (95% CI: 1.64, 2.28). For current smokers who smoked 1–14 cigarettes/day, the relative risk was 1.81 (95% CI: 1.38, 2.36); for those who smoked 15–24 cigarettes/day, the relative risk was 2.04 (95% CI: 1.68, 2.47); and for those who smoked 25 or more cigarettes/day, the relative risk was 2.29 (95% CI: 1.74, 3.01). There was a trend toward an increased risk of psoriasis with increasing pack-years or duration of smoking (Ptrend < 0.0001). The risk was highest among smokers who had 65 or more pack-years of smoking (relative risk = 2.72, 95% CI: 2.05, 3.60) and among those with a smoking duration of 30 or more years (relative risk = 1.99, 95% CI: 1.75, 2.25). The authors observed a graded reduction of risk with an increase in time since smoking cessation (Ptrend <0.0001). In this study, smoking was found to be an independent risk factor for psoriasis in both women and men. Psoriasis risk was particularly augmented for heavy smokers and persons with longer durations of smoking.
Abstract 8 of 13Original ContributionAbstract 8 of 13 Physical Activity, Sedentary Behavior, and Leukocyte Telomere Length in Women Leukocyte telomere length (LTL) is a potential indicator of cellular aging; however, its relation to physical activity and sedentary behavior is unclear. The authors examined cross-sectionally associations among activity, sedentary behavior, and LTL among 7,813 women aged 43–70 years in the Nurses’ Health Study. Participants self-reported activity by questionnaire in 1988 and 1992 and sedentary behavior in 1992. Telomere length in peripheral blood leukocytes, collected in 1989–1990, was measured by quantitative polymerase chain reaction. The least- squares mean telomere length (z-score) was calculated after adjustment for age and other potential confounders. For total activity, moderately or highly active women had a 0.07-standard deviation (SD) increase in LTL (2-sided Ptrend = 0.02) compared with those least active. Greater moderate- or vigorous-intensity activity was also associated with increased LTL (SD = 0.11 for 2–4 vs. <1 hour/week and 0.04 for ≥7 vs. <1 hour/week; 2-sided Ptrend = 0.02). Specifically, calisthenics or aerobics was associated with increased LTL (SD = 0.10 for ≥2.5 vs. 0 hours/week; 2-sided Ptrend = 0.04). Associations remained after adjustment for body mass index. Other specific activities and sitting were unassociated with LTL. Although associations were modest, these findings suggest that even moderate amounts of activity may be associated with longer telomeres, warranting further investigation in large prospective studies.
Abstract 9 of 13Original ContributionAbstract 9 of 13 Endogenous Reproductive Hormones and C-reactive Protein Across the Menstrual Cycle The BioCycle Study C-reactive protein (CRP) is one of the most commonly used markers of acute phase reaction in clinical settings and predictors of cardiovascular risk in healthy women; however, data on its physiologic regulation in premenopausal women are sparse. The objective of this study was to evaluate the association between endogenous reproductive hormones and CRP in the BioCycle Study (2005–2007). Women aged 18–44 years from western New York were followed prospectively for up to 2 menstrual cycles (n = 259). Serum levels of CRP, estradiol, progesterone, luteinizing hormone, and follicle- stimulating hormone were measured up to 8 times per cycle, timed by fertility monitors. CRP levels varied significantly across the cycle (P 3 mg/L) during menses compared with other phases (12.3% vs. 7.4%; P < 0.001). A 10-fold increase in estradiol was associated with a 24.3% decrease in CRP (95% confidence interval: 19.3, 29.0). A 10-fold increase in luteal progesterone was associated with a 19.4% increase in CRP (95% confidence interval: 8.4, 31.5). These results support the hypothesis that endogenous estradiol might have antiinflammatory effects and highlight the need for standardization of CRP measurement to menstrual cycle phase in reproductive-aged women.
Abstract 10 of 13Original ContributionAbstract 10 of 13 Hair Relaxer Use and Risk of Uterine Leiomyomata in African- American Women Hair relaxers are used by millions of black women, possibly exposing them to various chemicals through scalp lesions and burns. In the Black Women’s Health Study, the authors assessed hair relaxer use in relation to uterine leiomyomata incidence. In 1997, participants reported on hair relaxer use (age at first use, frequency, duration, number of burns, and type of formulation). From 1997 to 2009, 23,580 premenopausal women were followed for incident uterine leiomyomata. Multivariable Cox regression was used to estimate incidence rate ratios and 95% confidence intervals. During 199,991 person-years, 7,146 cases of uterine leiomyomata were reported as confirmed by ultrasound (n = 4,630) or surgery (n = 2,516). The incidence rate ratio comparing ever with never use of relaxers was 1.17 (95% confidence interval (CI): 1.06, 1.30). Positive trends were observed for frequency of use (Ptrend < 0.001), duration of use (Ptrend = 0.015), and number of burns (Ptrend < 0.001). Among long-term users (≥10 years), the incidence rate ratios for frequency of use categories 3–4, 5–6, and ≥7 versus 1–2 times/year were 1.04 (95% CI: 0.92, 1.19), 1.12 (95% CI: 0.99, 1.27), and 1.15 (95% CI: 1.01, 1.31), respectively (Ptrend = 0.002). Risk was unrelated to age at first use or type of formulation. These findings raise the hypothesis that hair relaxer use increases uterine leiomyomata risk.
Abstract 11 of 13Original ContributionAbstract 11 of 13 Helicobacter pylori Infection and Colorectal Cancer Risk: Evidence From a Large Population-based Case-Control Study in Germany Evidence concerning the role of Helicobacter pylori infection in the development of colorectal cancer remains controversial. The authors assessed the association of H. pylori seroprevalence with risk of colorectal cancer in a large population-based case-control study from Germany in 2003–2007. Serum antibodies to H. pylori in general and the cytotoxin-associated gene A protein (CagA) were measured in 1,712 incident colorectal cancer cases and 1,669 controls. The association between H. pylori seroprevalence and colorectal cancer risk was estimated by logistic regression, with adjustment for potential confounders and stratification by age group, sex, anatomic subsites, and cancer stage. Overall, H. pylori seroprevalence was higher in cases (46.1%) than in controls (40.1%), resulting in an age- and sex-adjusted odds ratio of 1.30 (95% confidence interval (CI): 1.14, 1.50). Adjustment for established colorectal cancer risk factors decreased the odds ratio to 1.26 (95% CI: 1.09, 1.47), with a further reduction to 1.18 (95% CI: 1.01, 1.38) after additional adjustment for previous colorectal endoscopy. Stratified analyses showed risk elevation to be essentially confined to left-sided colorectal cancer, with an odds ratio of 1.22 (95% CI: 1.02, 1.45), suggesting that H. pylori infection may be associated with a small yet relevant risk increase in the left colorectum.
Abstract 12 of 13Original ContributionAbstract 12 of 13 Prenatal Exposure to Mercury and Infant Neurodevelopment in a Multicenter Cohort in Spain: Study of Potential Modifiers Vulnerability of the central nervous system to mercury is increased during early development. This study aimed to evaluate whether cord blood total mercury levels may have a negative effect on both mental and psychomotor development in a maternal-birth cohort from moderate-high fish consumption areas. Study subjects were 1,683 child participants in the INMA (Environment and Childhood) Project from 4 areas of Spain between 2003 and 2010. Cord blood total mercury levels were analyzed by atomic absorption spectrometry. Infant neurodevelopment was assessed around age 14 months by the Bayley Scales of Infant Development. Sociodemographic, lifestyle, and dietary information was obtained by questionnaire during pregnancy. The geometric mean of total mercury levels was 8.4 μg/L (95% confidence interval (CI): 8.1, 8.7). In multivariate analysis, a doubling in total mercury levels did not show an association with mental (β = 0.1, 95% CI: −0.68, 0.88) or psychomotor (β = −0.05, 95% CI: −0.79, 0.68) developmental delay; however, stratified findings by sex suggest a negative association between prenatal exposure to total mercury and psychomotor development among female infants (β = −1.09, 95% CI: −2.21, 0.03), although follow-up is required to confirm these results.
Abstract 13 of 13Original ContributionAbstract 13 of 13 Strength of Association for Incident Diabetes Risk Factors According to Diabetes Case Definitions The Atherosclerosis Risk in Communities Study Prospective epidemiologic studies have characterized major risk factors for incident diabetes by a variety of diabetes case definitions. Whether different definitions alter the association of diabetes with risk factors is largely unknown. Using 1987–1998 data from the ongoing Atherosclerosis Risk in Communities (ARIC) Study, the authors assessed the relation of traditional risk factors with 3 different diabetes case definitions and 4 fasting glucose categories. They compared the study protocol case definition with 2 nested case definitions, self- reported diabetes and a multiple-evidence definition. Significant differences in risk factor associations by case definition and by screening cutpoints were observed. Specifically, the magnitude of the association between the risk factors (baseline metabolic syndrome, fasting glucose, blood pressure, body mass index, and serum insulin) and incident diabetes differed by case definition. Associations with these risk factors were weaker with a case definition based on self- report compared with other definitions. These results illustrate the potential limitations of case definitions that rely solely on self-report or those that incorporate measured glucose values to ascertain undiagnosed cases. Although the ability to identify risk factors of diabetes was consistent for the case definitions studied, tests of novel risk factors may result in different estimates of effect sizes depending on the definition used.