Poisson Log-linear Regression Models Research Articles

HIV-1 Drug Resistance Evolution Among Patients on Potent Combination Antiretroviral Therapy With Detectable Viremia

Many patients infected with HIV do not achieve or maintain virologic suppression below levels of detection while on potent combination antiretroviral therapy. The likelihood of emergence of incident mutations conferring reduced antiretroviral drug susceptibility was estimated among patients maintained on a stable regimen with ongoing detectable plasma HIV RNA levels. Ninety-eight HIV-infected patients were identified who had 2 genotypic antiretroviral resistance tests available. Poisson log-linear regression models were used to identify predictors and estimate incidence rates of number of acquired antiretroviral drug resistance mutations per person-year. At the 1st resistance test, 88% of patients had evidence of at least 1 mutation. Sixty percent of patients acquired at least 1 new mutation during a median of 9.3 months between consecutive resistance tests, with an incidence rate of 1.61 acquired mutations per person-year (95% CI: 1.36-1.90). Predictors of resistance evolution included average plasma HIV RNA level, HIV RNA slope, and number of mutations detected at the 1st resistance test. The likelihood of acquiring drug resistance mutations while remaining on potent combination antiretroviral therapy that does not confer complete suppression of HIV replication is relatively low and depends on the level of viral replication and prior resistance.

Food Safety and Inspection Service Regulatory Testing Program for Escherichia coli O157:H7 in Raw Ground Beef

We analyzed raw ground beef testing data to determine whether a decrease in the rate of Escherichia coli O157:H7–positive raw ground beef samples has occurred since the inception of Food Safety and Inspection Service (U.S. Department of Agriculture) regulatory actions and microbiological testing concerning this commodity and pathogen. A main effects log-linear Poisson regression model was constructed to evaluate the association between fiscal year and the rate of E. coli O157: H7–positive raw ground beef samples while controlling for the effect of season for the subset of test results obtained from fiscal year (FY)2000 through FY2003. Rate ratios were used to compare the rate of E. coli O157:H7–positive raw ground beef samples between sequential years to identify year-to-year differences. Of the 26,521 raw ground beef samples tested from FY2000 through FY2003, 189 (0.71%) tested positive for E. coli O157:H7. Year-to-year comparisons identified a 50% reduction in the rate of positive ground beef samples from FY2002 to FY2003 when controlling for season (95% CI, 10 to 72% decrease; P = 0.02). This decrease was the only significant year-to-year change in the rate of E. coli O157:H7–positive raw ground beef samples but was consistent in samples obtained from both federally inspected establishments and retail outlets. We believe this decrease is attributed to specific regulatory actions by Food Safety and Inspection Service and subsequent actions implemented by the industry, with the goal of reducing E. coli O157:H7 adulteration of raw ground beef. Continued monitoring is necessary to confirm that the decrease in the rate of E. coli O157:H7 in raw ground beef samples we observed here represents the beginning of a sustained trend.

Changes in public order after the opening of a medically supervised safer injecting facility for illicit injection drug users.

North America's first medically supervised safer injecting facility for illicit injection drug users was opened in Vancouver on Sept. 22, 2003. Although similar facilities exist in a number of European cities and in Sydney, Australia, no standardized evaluations of their impact have been presented in the scientific literature. Using a standardized prospective data collection protocol, we measured injection-related public order problems during the 6 weeks before and the 12 weeks after the opening of the safer injecting facility in Vancouver. We measured changes in the number of drug users injecting in public, publicly discarded syringes and injection-related litter. We used Poisson log-linear regression models to evaluate changes in these public order indicators while considering potential confounding variables such as police presence and rainfall. In stratified linear regression models, the 12-week period after the facility's opening was independently associated with reductions in the number of drug users injecting in public (p < 0.001), publicly discarded syringes (p < 0.001) and injection-related litter (p < 0.001). The predicted mean daily number of drug users injecting in public was 4.3 (95% confidence interval [CI] 3.5-5.4) during the period before the facility's opening and 2.4 (95% CI 1.9-3.0) after the opening; the corresponding predicted mean daily numbers of publicly discarded syringes were 11.5 (95% CI 10.0-13.2) and 5.4 (95% CI 4.7-6.2). Externally compiled statistics from the city of Vancouver on the number of syringes discarded in outdoor safe disposal boxes were consistent with our findings. The opening of the safer injecting facility was independently associated with improvements in several measures of public order, including reduced public injection drug use and public syringe disposal.

Evolution of resistance to drugs in HIV-1-infected patients failing antiretroviral therapy

The optimal time for changing failing antiretroviral therapy (ART) is not known. It involves balancing the risk of exhausting future treatment options against the risk of developing increased drug resistance. The frequency with which new drug-resistance mutations (DRM) developed and their potential consequences in patients continuing unchanged treatment despite persistent viremia were assessed. A retrospective study of consecutive sequence samples from 106 patients at one institution with viral load (VL) of more than 400 copies/ml, with no change in ART for more than 2 months despite virologic failure. Two consecutive pol sequences, CD4 cell counts and VL were analyzed to quantify the development of new DRM and to identify changes in immunologic and virologic parameters. Genotypic susceptibility scores (GSS) and viral drug susceptibilities were calculated by a computer program (HIVDB). Poisson log-linear regression models were used to predict the expected number of mutations at the second time point. : After a median of 14 months of continued ART, 75% (80 of 106) of patients acquired new DRM and were assigned a significantly lower GSS, potentially limiting the success of future ART. The development of new DRM was proportional to the time between the two sequences and inversely proportional to the number of DRM in the first sequence. However, the development of DRM was not associated with significant changes in CD4 or VL counts. Despite stable levels of CD4 and VL over time, maintaining a failing therapeutic regimen increases drug resistance and may limit future treatment options.

USING EVAPORATIVE COOLING TO REDUCE THE FREQUENCY AND DURATION OF ELEVATED TEMPERATUREHUMIDITY INDICES IN OKLAHOMA

Extreme temperatures and humidities can be harmful or even fatal to livestock if proper precautions are not taken.An indicator often used to measure stressful conditions is the Temperature-Humidity Index (THI). Using seven years of hourlydata from 17 sites in Oklahoma, total annual hours were determined for THI . 84 and THI . 79. To provide a tool to determinethe effect of employing evaporative cooling to reduce THI levels, a Poisson loglinear regression model was used to predictthe average annual hours that an evaporative cooler could reduce THI levels to below 79. Predicted rates of reduction in THIranged from 64.3% to 100%.

Differences in the epidemic rise and decrease of prostate cancer among geographical areas in Southern Europe: an analysis of differential trends in incidence and mortality in France, Italy and Spain

This is a population-based study aimed at evaluating incidence and mortality trends for prostate cancer in France, Italy and Spain, during the prostate-specific antigen (PSA) era, considering elderly people aged 70 years and over and younger adults aged between 40 and 69 years. Trends were estimated by a log-linear Poisson regression model and expressed as an Estimated Annual Percent Change (EAPC). Incidence increased sharply in almost all areas. Spain showed the lowest increases. Incidence started to rise around 1985 in France and after 1990 in Italy and Spain. Mortality increased until the late 1980s in all countries, then declined in France and Italy (−2.5% in 40–69 year age group), but not in Spain. Younger people showed a much higher rise in incidence than the elderly, while mortality decreased mainly in the younger adults. The decrease in mortality was more marked in those areas and the younger age group where the rise in incidence was higher and started earlier, i.e. in France and in younger people, suggesting that the PSA test may have had a positive effect on mortality, although other clinical advances also have to be taken into account.

Prostate cancer incidence and mortality trends among elderly and adult Europeans

Prostate cancer is a common malignancy primarily of elderly men, with incidence rates rapidly increasing, owing to the population ageing and the introduction of more sensitive diagnostic procedures. Although the effectiveness of a screening test remains controversial, the decreasing mortality rates, which recently emerged in the USA, may be partly attributable to the changes of patterns of care, thus suggesting a potential effect of preventive measure. The object of this study is to examine time trends in incidence and mortality from prostate cancer in European Union (EU) countries, with particular attention to possible differences between the elderly (65 years old or over) and younger or middle age adults (35–64 years old). EUROCIM, the data base created by the European Network of Cancer Registries, provided the incidence and mortality data for the 12 EU Countries analysed (namely: Finland, Denmark, Scotland, England and Wales, Ireland and The Netherlands in Northern Europe; Austria, Germany and France in Central Europe; Italy, Spain and Portugal in Southern Europe), for the 1978–1994 period. Incidence and mortality time trends, expressed as mean difference per cent (MD%) per year, were estimated by a Poisson log-linear regression model. Higher resolution analyses were also carried out to check differences in time trends by age class within the two groups under study. Upward mortality trends occurred in several countries, excepting Ireland, Austria and Southern Europe, but only for younger and middle aged adults. Rates increased more rapidly in older age groups; a clear north–south gradient appeared both in the elderly and in younger adults; for the elderly, MD% higher than +1.5 for most countries of Northern Europe, MD% around +1 for Central Europe, and MD% less than +1 for Southern Europe were registered, with lower values for younger people. Incidence rates rose across the period considered, almost in all countries both for elderly and for younger and middle age adults, increasing more rapidly in younger age. Incidence trends showed a less clear geographic pattern than for mortality. In the younger group, high MD%, ranging in Northern Europe from +3.2 in Finland and England and Wales to +5.7 in The Netherlands, were observed, while in the South values ranged between +4.2 and +5.0. In Central Europe, very high MD%, ranging between +8.4 in France and +16.6 in Austria, were noted. No significant trends were observed for Denmark, Ireland and Portugal. For the elderly the increase was generally lower and no significant trend was observed in Germany and Portugal. Interaction between age and calendar period in the older group was observed for most of the considered countries. With reference to mortality, the MD% showed a tendency to rise, with increasing age, while no consistent pattern emerged for incidence. The observed incidence trends are probably a consequence of the different times in which the more recent detection methods were introduced in each country, and of the different policies adopted by each health care system towards the elderly. A comparison with the USA data suggests that in the next future a favourable downward mortality trend could be expected also in some EU Countries and, particularly, for younger age groups, even though prostatic cancer in old patients will remain a great burden, which National Health Care Systems will have to face in the next decades.

Urban air pollution and cardiopulmonary ill health: a 14.5 year time series study.

OBJECTIVES: To examine possible associations between daily concentrations of urban air pollutants and hospital emergency admissions and mortality due to cardiac and pulmonary disease. METHODS: A time series study was...

Cancer mortality by urbanization and proximity to the sea coast in Campania Region, southern Italy.

The risk for several cancers is higher in urban than in rural areas. The gradient has seldom been studied in southern Europe. The geographical pattern of mortality for different cancers and all causes was studied in the Campania Region (about 5.6 million inhabitants), whose largest town is Naples. The key variables were residence in urban/rural and coastal/inland municipalities. Relative risks of death and corresponding 95% confidence intervals by residence were evaluated by means of Poisson log-linear regression models. Significantly increased mortality rates in urban compared to rural municipalities were found for several cancer causes of death. In particular, in both sexes, excesses in the order of 30-50% were observed for tobacco-related neoplasms (i.e., larynx, lung, and bladder) and cancers of the intestine, liver, brain, multiple myeloma and non-Hodgkin's lymphoma, in addition to all-cancer, and all-cause mortality. In females, specific excesses were also noticed for cancer of the gallbladder, pancreas, breast and uterus (corpus and cervix). Conversely, significantly decreased mortality rates in urban with respect to rural municipalities were observed for cancer of the oral cavity and pharynx in males. Coastal location and degree of urbanization were strongly correlated, thus showing similar associations with most causes of death. However, a significant excess of cancer of the pleura in males was restricted to coastal municipalities. Anti-smoking campaigns, sanitation improvements, hepatitis B vaccination, and a decrease in obesity emerge as high priorities with respect to cancer control strategies in the Campania Region, particularly in overpopulated, underprivileged urban areas.

Birth order, sibship size and risk of Hodgkin's disease in children and young adults: a population-based study of 31 million person-years.

It has been proposed that Hodgkin's disease (HD) may have an infectious origin and that delayed exposure to infection may increase the risk of HD in young adults. This hypothesis is addressed by studying the family structure among children and young adults. The Civil Registration System was used to establish a population-based cohort consisting of all persons whose mothers were born in Denmark since 1935. Persons who developed HD were identified by linkage with the Danish Cancer Registry. HD incidence rate ratios were estimated based on a log-linear Poisson regression model. The cohort of 2.1 million persons (aged 0-42 years) was followed for 31.1 million person years, during which period 378 cases of HD occurred. Among children (< 15 years, n = 72), the relative risk (RR) of HD tended to increase with increasing sibship size, the relative increase in risk per increase in sibship size (the trend) being 1.28 [95% confidence interval (CI) 1.00-1.63]. The trend for birth order was 1.26 (95% CI 0.92-1.73). Among young adults (> or = 15 years, n = 306) the risk of HD, on the contrary, tended to decrease with increasing sibship size [trend = 0.91 (95% CI, 0.81-1.03)] and birth order (trend = 0.85 (95% CI, 0.71-1.01). These trends among young adults were significantly different from the corresponding trends among children (p < 0.05). Siblings of cases were at increased risk of HD (RR = 18; 95% CI, 2.2-65, n = 2). Our findings are compatible with the hypothesis that delayed exposure to infection may be a risk factor for HD in young adults, and that early exposure perhaps to another infectious agent may increase the risk of HD in children.