A method for statistically comparing spatial distribution maps

<p>Abstract</p> <p>Background</p> <p>Ecological niche modeling is a method for estimation of species distributions based on certain ecological parameters. Thus far, empirical determination of significant differences between independently generated distribution maps for a single species (maps which are created through equivalent processes, but with different ecological input parameters), has been challenging.</p> <p>Results</p> <p>We describe a method for comparing model outcomes, which allows a statistical evaluation of whether the strength of prediction and breadth of predicted areas is measurably different between projected distributions. To create ecological niche models for statistical comparison, we utilized GARP (Genetic Algorithm for Rule-Set Production) software to generate ecological niche models of human monkeypox in Africa. We created several models, keeping constant the case location input records for each model but varying the ecological input data. In order to assess the relative importance of each ecological parameter included in the development of the individual predicted distributions, we performed pixel-to-pixel comparisons between model outcomes and calculated the mean difference in pixel scores. We used a two sample Student's t-test, (assuming as null hypothesis that both maps were identical to each other regardless of which input parameters were used) to examine whether the mean difference in corresponding pixel scores from one map to another was greater than would be expected by chance alone. We also utilized weighted kappa statistics, frequency distributions, and percent difference to look at the disparities in pixel scores. Multiple independent statistical tests indicated precipitation as the single most important independent ecological parameter in the niche model for human monkeypox disease.</p> <p>Conclusion</p> <p>In addition to improving our understanding of the natural factors influencing the distribution of human monkeypox disease, such pixel-to-pixel comparison tests afford users the ability to empirically distinguish the significance of each of the diverse environmental parameters included in the modeling process. This method will be particularly useful in situations where the outcomes (maps) appear similar upon visual inspection (as are generated with other modeling programs such as MAXENT), as it allows an investigator the capacity to explore subtle differences among ecological parameters and to demonstrate the individual importance of these factors within an overall model.</p

A Methodological Approach to Assessing the Health Impact of Environmental Chemical Mixtures: PCBs and Hypertension in the National Health and Nutrition Examination Survey

We describe an approach to examine the association between exposure to chemical mixtures and a health outcome, using as our case study polychlorinated biphenyls (PCBs) and hypertension. The association between serum PCB and hypertension among participants in the 1999–2004 National Health and Nutrition Examination Survey was examined. First, unconditional multivariate logistic regression was used to estimate odds ratios and associated 95% confidence intervals. Next, correlation and multicollinearity among PCB congeners was evaluated, and clustering analyses performed to determine groups of related congeners. Finally, a weighted sum was constructed to represent the relative importance of each congener in relation to hypertension risk. PCB serum concentrations varied by demographic characteristics, and were on average higher among those with hypertension. Logistic regression results showed mixed findings by congener and class. Further analyses identified groupings of correlated PCBs. Using a weighted sum approach to equalize different ranges and potencies, PCBs 66, 101, 118, 128 and 187 were significantly associated with increased risk of hypertension. Epidemiologic data were used to demonstrate an approach to evaluating the association between a complex environmental exposure and health outcome. The complexity of analyzing a large number of related exposures, where each may have different potency and range, are addressed in the context of the association between hypertension risk and exposure to PCBs

Effect of ethnicity on access and device complications during endovascular aneurysm repair

AbstractIntroductionThere are no published reports on the association between ethnicity and outcome after aortoiliac stent grafting to treat aneurismal disease. Because Hawaii is a state with an ethnically diverse population, we conducted a retrospective study to examine this potential association. We hypothesized that individuals of Asian ancestry may have higher complication rates after endovascular repair compared with non-Asians.MethodsAll endovascular devices placed to treat aneurysm disease from 1996 to 2003 were evaluated in two institutions. The association between ethnicity and access-related and device-related complications, both periprocedural and delayed, was examined with logistic regression analysis.ResultsNinety-two aortoiliac endografts were placed during the study period, including 87 in patients with abdominal aortic aneurysms with or without iliac aneurysm disease, and five patients with isolated iliac artery aneurysms. Forty-four percent of patients were categorized as Asian, 39% as white, 16% as Pacific Islander, and 1% as African American. Access-related and device-related complications (ADRCs) occurred in 11 of 92 (12%) of these patients. The following parameters were significantly associated with ADRCs: Asian ethnicity (P =.015), age greater than 80 years (P = .02), and external iliac diameter smaller than 7.5 mm (P =.01). Asian patients were more likely to have experienced ADRCs than were non-Asian patients (odds ratio, 7.3; 95% confidence interval, 1.5-35.8; P = .015). Asians also had smaller external iliac artery diameters (P = .0003) and more tortuous iliac arteries (P = .03) compared with non-Asians. After adjusting for iliac artery diameter and tortuosity, the association between Asian ethnicity and ARDCs became nonsignificant (P = .074), which suggests that the association between race and complications may be at least in part due to small and tortuous iliac arteries. There was no association between age, gender, or ethnicity and postoperative detection of endoleak.ConclusionOur data indicate that individuals of Asian ancestry are far more likely to experience adverse access-related and device-related complications after aortoiliac stent grafting than are non-Asians. We found that this association is at least partly attributable to the smaller and more tortuous iliac arteries in persons of Asian ancestry

Increasing Rate of Pneumonia Hospitalizations among Older American Indian and Alaska Native Adults

Objective: To examine rates and trends of pneumonia hospitalization among older American Indian and Alaska Native (AI/AN) adults. Methods: Pneumonia hospitalizations for older AI/AN adults ≥65 years of age living in the Alaska and Southwest Indian Health Service (IHS) regions during 1988 through 2002 from the IHS hospital discharge data were analyzed. Results: The average annual hospitalization rate for first-listed pneumonia for older AI/AN adults in both the Alaska and the Southwest regions has increased (15.3 and 23.0 in 1988-1990 to 25.9 and 28.8 in 2000-2002 per 1,000 population, respectively), with the greatest increase seen among older AI/AN adults in the Alaska region. For both regions, the hospitalization rate increased with increasing age. The proportion of pneumonia hospitalizations with the co-morbid conditions of chronic heart disease, chronic lung disease and diabetes mellitus in the Alaska and the Southwest regions increased from 48.8% and 30.8% in 1988-1990 to 65.4% and 40.7% in 2000-2002, respectively. Conclusions: The rate of pneumonia hospitalizations among older AI/AN adults in the Alaska and the Southwest regions has increased substantially; the 2000-2002 rate was similar to or slightly higher than those reported for the general older US population. This rate increase and the increasing prevalence of chronic co-morbid conditions indicate a need for prevention efforts and health interventions among older AI/AN adults

Trends in Hospitalizations for Peptic Ulcer Disease, United States, 1998–20051

TOC summary: Decreased hospitalization rates suggest decline in complications from Helicobacter pylori infection

The Incidence of Molluscum contagiosum among American Indians and Alaska Natives

The epidemiology of Molluscum contagiosum (MC) in the United States is largely unknown, despite the fact that the virus is directly communicable and large outbreaks occur. This study provides population-based estimates to describe the epidemiology of MC in the United States among American Indian and Alaska Native (AI/AN) persons. This population was selected because of the comprehensiveness and quality of available data describing utilization of out-patient services.Outpatient visits listing MC as a diagnosis in the Indian Health Service National Patient Information Reporting System during 2001-2005 were analyzed to assess patient characteristics, visit frequency and concurrent skin conditions. Outpatient visit rates and incidence rates were calculated based on known population denominators (retrospective cohort). Overall outpatient visit rates were also calculated for the general US population using national data. The average annual rate of MC-associated outpatient visits was 20.15/10,000 AI/AN persons for 2001-2005 (13,711 total visits), which was similar to the rate for the general US population (22.0/10,000 [95% CI: 16.9-27.1]). The incidence of MC-associated visits was 15.34/10,000. AI/AN children 1-4 years old had the highest incidence (77.12), more than twice that for children 5-14 years old (30.79); the incidence for infants (<1 year) was higher than that for adults. AI/AN persons living in the West region had the highest incidence, followed by those in the East and Alaska regions (26.96, 22.88 and 21.38, respectively). There were age-specific associations between MC and concurrent skin conditions (e.g., atopic dermatitis, eczema).This study highlights the need for periodic population-based measurements to assess trends in incidence and healthcare utilization for MC in the United States. High rates of MC were found among AI/AN persons, especially among children <15 years old. The AI/AN population would benefit from greater availability of effective strategies for prevention and treatment of MCV infection

Ecological Niche and Geographic Distribution of Human Monkeypox in Africa

Monkeypox virus, a zoonotic member of the genus Orthopoxviridae, can cause a severe, smallpox-like illness in humans. Monkeypox virus is thought to be endemic to forested areas of western and Central Africa. Considerably more is known about human monkeypox disease occurrence than about natural sylvatic cycles of this virus in non-human animal hosts. We use human monkeypox case data from Africa for 1970–2003 in an ecological niche modeling framework to construct predictive models of the ecological requirements and geographic distribution of monkeypox virus across West and Central Africa. Tests of internal predictive ability using different subsets of input data show the model to be highly robust and suggest that the distinct phylogenetic lineages of monkeypox in West Africa and Central Africa occupy similar ecological niches. High mean annual precipitation and low elevations were shown to be highly correlated with human monkeypox disease occurrence. The synthetic picture of the potential geographic distribution of human monkeypox in Africa resulting from this study should support ongoing epidemiologic and ecological studies, as well as help to guide public health intervention strategies to areas at highest risk for human monkeypox

The risk of lung cancer related to dietary intake of flavonoids

It has been hypothesized that flavonoids in foods and beverages may reduce cancer risk through antioxidation, inhibition of inflammation, and other antimutagenic and antiproliferative properties. We examined associations between intake of five flavonoid subclasses (anthocyanidins, flavan-3-ols, flavones, flavonols, flavanones) and lung cancer risk in a population-based case-control study in Montreal, Canada (1,061 cases and 1,425 controls). Flavonoid intake was estimated from a food frequency questionnaire that assessed diet two years prior to diagnosis (cases) or interview (controls). Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using unconditional logistic regression. Overall, total flavonoid intake was not associated with lung cancer risk, the effect being similar regardless of sex and smoking level. However, low flavonoid intake from food, but not from beverages, was associated with an increased risk. The adjusted ORs (95% CIs) comparing the highest versus the lowest quartiles of intake were 0.63 (0.47-0.85) for total flavonoids, 0.82 (0.61-1.11) for anthocyanidins, 0.67 (0.50-0.90) for flavan-3-ols, 0.68 (0.50-0.93) for flavones, 0.62 (0.45-0.84) for flavonols, and 0.70 (0.53-0.94) for flavanones. An inverse association with total flavone and flavanone intake was observed for squamous cell carcinoma but not adenocarcinoma. In conclusion, low flavonoid intake from food may increase lung cancer risk