Socioeconomic differences in dietary patterns among middle-aged men and women

The aim of the study is to (i) identify common dietary patterns, (ii) study socioeconomic differences in these dietary patterns, and (iii) assess whether they contribute to socioeconomic differences in biological risk factors. The data come from the Whitehall II study of London civil servants, who participated in the third phase (1991-1993) and were 39-63-years old (N=8004). Food frequency questionnaire and socioeconomic background information was from a questionnaire, and biological risk factors from a medical screening. Six dietary patterns were identified. In reference to high employment grade men, the odds ratios of low grade men consuming the 'unhealthy' or the 'very unhealthy' diet were 1.26 and 3.34, respectively, while the odds for the 'French' diet was 0.13. Among women the corresponding odds were 2.98, 6.19 and 0.25. Adjusting for spouse's socioeconomic status and to a lesser extent smoking and exercise as well as job control attenuate these grade differences somewhat. Among men and women adjusting for dietary patterns accounted for about 25-50 per cent of grade differences in HDL and serum triglyceride levels.     

A comparison of propensity score methods: a case-study estimating the effectiveness of post-AMI statin use

There is an increasing interest in the use of propensity score methods to estimate causal effects in observational studies. However, recent systematic reviews have demonstrated that propensity score methods are inconsistently used and frequently poorly applied in the medical literature. In this study, we compared the following propensity score methods for estimating the reduction in all-cause mortality due to statin therapy for patients hospitalized with acute myocardial infarction: propensity-score matching, stratification using the propensity score, covariate adjustment using the propensity score, and weighting using the propensity score. We used propensity score methods to estimate both adjusted treated effects and the absolute and relative risk reduction in all-cause mortality. We also examined the use of statistical hypothesis testing, standardized differences, box plots, non-parametric density estimates, and quantile-quantile plots to assess residual confounding that remained after stratification or matching on the propensity score. Estimates of the absolute reduction in 3-year mortality ranged from 2.1 to 4.5 per cent, while estimates of the relative risk reduction ranged from 13.3 to 17.0 per cent. Adjusted estimates of the reduction in the odds of 3-year death varied from 15 to 24 per cent across the different propensity score methods.     

Measuring the impact of conjugate vaccines on invasive Haemophilus influenzae type b infection in Western Australia

Abstract: Haemophilus influenzae type b (Hib) causes serious infections in 26–59 per 100 000 non–Aboriginal Australian children under five years of age. Aboriginal children suffer much higher rates of infection (≥ 150 per 100 000), and at an earlier age, and have a greater risk of death and disability due to Hib infection. In 1992 and 1993, four conjugate Hib vaccines were introduced in Australia, and a nationally funded program of infant vaccination was begun in July 1993. This study aimed at evaluating the effectiveness of Hib vaccination in Aboriginal and non–Aboriginal children in Western Australia using a population–based active surveillance system for non–Aboriginal children and a case control study for Aboriginal children. The incidence of invasive Hib disease in non–Aboriginal children fell from 30.9 per 100 000 before vaccination was available to 6.3 per 100 000 in the second year after its introduction. The vaccine efficacy was estimated to be 80 per cent for Aboriginal children (odds ratio 0.20, 95 per cent CI 0.01–2.76) and, after adjustment for confounders, 75 per cent (odds ratio 0.25, CI 0.02–3.66). Based on the adjusted value (75 per cent), and using a Bayesian approach, we estimate that the posterior probability was 0.55 that the true vaccine efficacy is greater than 70 per cent, and 0.69 that the efficacy is greater than 50 per cent. We conclude that Hib vaccination is effective in preventing invasive Hib disease in Aboriginal and non–Aboriginal children in Australia. Aust N Z J Public Health 1998; 22: 67–72)     

COMPARING METHODS FOR CALCULATING CONFIDENCE INTERVALS FOR VACCINE EFFICACY

A method is introduced for computing a Bayesian 95 per cent posterior probability region for vaccine efficacy. This method assumes independent vague gamma prior distributions for the incidence rates on each arm of the trial, and a Poisson likelihood for the counts of incident cases of infection. The approach is similar in spirit to the Bayesian analysis of the binomial risk ratio described by Aitchison and Bacon-Shone. However, the focus of our interest is not on incorporating prior information into the design of trials for efficacy, but rather on evaluating whether or not the Bayesian approach with vague prior information produces comparable results to a frequentist approach. A review of methods for constructing exact and large sample intervals for vaccine efficacy is provided as a framework for comparison. The confidence interval methods are assessed by comparing the size and power of tests of vaccine efficacy in proposed intermediate sized randomized double blinded placebo controlled trials.     

Estimating HIV incidence rates from age prevalence data in epidemic situations.

We present a method of estimating HIV incidence rates in epidemic situations from data on age-specific prevalence and changes in the overall prevalence over time. The method is applied to women attending antenatal clinics in Hlabisa, a rural district of KwaZulu/Natal, South Africa, where transmission of HIV is overwhelmingly through heterosexual contact. A model which gives age-specific prevalence rates in the presence of a progressing epidemic is fitted to prevalence data for 1998 using maximum likelihood methods and used to derive the age-specific incidence. Error estimates are obtained using a Monte Carlo procedure. Although the method is quite general some simplifying assumptions are made concerning the form of the risk function and sensitivity analyses are performed to explore the importance of these assumptions. The analysis shows that in 1998 the annual incidence of infection per susceptible woman increased from 5.4 per cent (3.3-8.5 per cent; here and elsewhere ranges give 95 per cent confidence limits) at age 15 years to 24.5 per cent (20.6-29.1 per cent) at age 22 years and declined to 1.3 per cent (0.5-2.9 per cent) at age 50 years; standardized to a uniform age distribution, the overall incidence per susceptible woman aged 15 to 59 was 11.4 per cent (10.0-13.1 per cent); per women in the population it was 8.4 per cent (7.3-9.5 per cent). Standardized to the age distribution of the female population the average incidence per woman was 9.6 per cent (8.4-11.0 per cent); standardized to the age distribution of women attending antenatal clinics, it was 11.3 per cent (9.8-13.3 per cent). The estimated incidence depends on the values used for the epidemic growth rate and the AIDS related mortality. To ensure that, for this population, errors in these two parameters change the age specific estimates of the annual incidence by less than the standard deviation of the estimates of the age specific incidence, the AIDS related mortality should be known to within +/-50 per cent and the epidemic growth rate to within +/-25 per cent, both of which conditions are met. In the absence of cohort studies to measure the incidence of HIV infection directly, useful estimates of the age-specific incidence can be obtained from cross-sectional, age-specific prevalence data and repeat cross-sectional data on the overall prevalence of HIV infection. Several assumptions were made because of the lack of data but sensitivity analyses show that they are unlikely to affect the overall estimates significantly. These estimates are important in assessing the magnitude of the public health problem, for designing vaccine trials and for evaluating the impact of interventions.     

The performance of different propensity score methods for estimating marginal odds ratios

The propensity score which is the probability of exposure to a specific treatment conditional on observed variables. Conditioning on the propensity score results in unbiased estimation of the expected difference in observed responses to two treatments. In the medical literature, propensity score methods are frequently used for estimating odds ratios. The performance of propensity score methods for estimating marginal odds ratios has not been studied. We performed a series of Monte Carlo simulations to assess the performance of propensity score matching, stratifying on the propensity score, and covariate adjustment using the propensity score to estimate marginal odds ratios. We assessed bias, precision, and mean-squared error (MSE) of the propensity score estimators, in addition to the proportion of bias eliminated due to conditioning on the propensity score. When the true marginal odds ratio was one, then matching on the propensity score and covariate adjustment using the propensity score resulted in unbiased estimation of the true treatment effect, whereas stratification on the propensity score resulted in minor bias in estimating the true marginal odds ratio. When the true marginal odds ratio ranged from 2 to 10, then matching on the propensity score resulted in the least bias, with a relative biases ranging from 2.3 to 13.3 per cent. Stratifying on the propensity score resulted in moderate bias, with relative biases ranging from 15.8 to 59.2 per cent. For both methods, relative bias was proportional to the true odds ratio. Finally, matching on the propensity score tended to result in estimators with the lowest MSE.     

Hepatitis B infection in a day school for mentally retarded students: transmission from students to staff

We carried out a seroepidemiologic study to evaluate the transmission of hepatitis B virus (HBV) from students to staff in a day school for mentally retarded students. Of 505 students tested, 37 (7.3 per cent) had HBsAg; 74 per cent of HBsAg-positive sera tested were HBeAg-positive. Of 162 staff members tested, 21 (13.0 per cent) were HBV marker positive and two (1.2 per cent) had HBsAg; specialized educators and teachers showed the highest HBV marker prevalence (22.2 per cent and 21.3 per cent, respectively). The prevalence of HBV markers among staff was independently associated with classroom contact with a HBsAg-positive student, duration of employment at the school, and previous work with mentally retarded individuals. The incidence of HBV infection among teaching staff with regular classroom contact, estimated by logistic regression analysis, was 2.6 per cent per year. This observation indicates that teaching staff in schools for mentally retarded students with direct classroom contact may carry an occupational risk of HBV infection.     

The generalization of the odds ratio, risk ratio and risk difference to r x k tables

Familiar measures of association for 2 x 2 tables are the odds ratio, the risk ratio and the risk difference. Analagous measures of outcome-exposure association are desirable when there are several degrees of severity of both exposure and disease outcome. One such measure (alpha), which we label the general odds ratio (OR(G)), was proposed by Agresti. Convenient methods are given for calculation of both standard error and 95 per cent confidence intervals for OR(G). Other approaches to generalizing the odds ratio entail fitting statistical models which might not fit the data, and cannot handle some zero frequencies. We propose a generalization of the risk ratio (RR(G)) following the statistical approaches of Agresti, Goodman and Kruskal. A method of calculating the standard error and 95 per cent confidence interval for RR(G) is provided. A known statistic, Somers' d, fulfils the characteristics necessary for a generalized risk difference (RD(G)). These measures have straightforward interpretations, are easily computed, are at least as precise as other methods and do not require fitting statistical models to the data. We also examine the pooling of such measures as in, for example, meta-analysis.     

Web page quality: can we measure it and what do we find? A report of exploratory findings

BACKGROUND: The aim of this study was to report exploratory findings from an attempt to quantify the quality of a sample of World Wide Web (WWW) pages relating to MMR vaccine that a typical user might locate. METHOD: Forty pages obtained from a search of the WWW using two search engines and the search expression 'mmr vaccine' were analysed using a standard proforma. The proforma looked at the information the pages contained in terms of three categories: content, authorship and aesthetics. The information from each category was then quantified into a summary statistic, and receiver operating characteristic (ROC) curves were generated using a 'gold standard' of quality derived from the published literature. Optimal cut-off points for each of the three sections were calculated that best discriminated 'good' from 'bad' pages. Pages were also assessed as to whether they were pro- or anti-vaccination. RESULTS: For this sample, the combined contents and authorship score, with a cut-off of five, was a good discriminator, having 88 per cent sensitivity and 92 per cent specificity. Aesthetics was not a good discriminator. In the sample, 32.5 per cent of pages were pro-vaccination; 42.5 per cent were anti-vaccination and 25 per cent were neutral. The relative risk of being of poor quality if anti-vaccination was 3.3 (95 per cent confidence interval 1.8, 6.1). CONCLUSION: The sample of Web pages did contain some quality information on MMR vaccine. It also contained a great deal of misleading, inaccurate data. The proforma, combined with a knowledge of the literature, may help to distinguish between the two.     

Human immunodeficiency virus infection in heterosexual intravenous drug users in San Francisco.

To investigate the risk of infection with the human immunodeficiency virus (HIV) in San Francisco, the prevalence of antibodies to HIV was determined in 281 heterosexual intravenous drug users recruited from community-based settings. Ten per cent of subjects had ELISA and Western blot confirmed seropositivity for antibodies (95 per cent CI 6.8-14.2 per cent). Analysis of behavioral factors revealed an increased risk of seropositivity in addicts who reported regularly sharing needles when injecting, particularly those sharing with two or more persons (odds ratio = 5.43; 95 per cent CI 1.08-52.5). Blacks and Latinos also had a greater prevalence of seropositivity than Whites, and this finding persisted after adjustment for needle sharing (adjusted odds ratio = 2.8; 95 per cent CI .84-8.59). Seropositivity was not associated with age, sex, duration of drug use, or history of prostitution. These data indicate that a new epidemic of AIDS (acquired immunodeficiency syndrome) in intravenous drug users, similar to that which has occurred among homosexuals in San Francisco, is possible. The relatively low seroprevalence in 1985 provides health officials an important opportunity to intervene and attempt to prevent widespread infection of drug users with HIV.     

Finding factors influencing risk: comparing Bayesian stochastic search and standard variable selection methods applied to logistic regression models of cases and controls

When modeling the risk of a disease, the very act of selecting the factors to be included can heavily impact the results. This study compares the performance of several variable selection techniques applied to logistic regression. We performed realistic simulation studies to compare five methods of variable selection: (1) a confidence interval (CI) approach for significant coefficients, (2) backward selection, (3) forward selection, (4) stepwise selection, and (5) Bayesian stochastic search variable selection (SSVS) using both informed and uniformed priors. We defined our simulated diseases mimicking odds ratios for cancer risk found in the literature for environmental factors, such as smoking; dietary risk factors, such as fiber; genetic risk factors, such as XPD; and interactions. We modeled the distribution of our covariates, including correlation, after the reported empirical distributions of these risk factors. We also used a null data set to calibrate the priors of the Bayesian method and evaluate its sensitivity. Of the standard methods (95 per cent CI, backward, forward, and stepwise selection) the CI approach resulted in the highest average per cent of correct associations and the lowest average per cent of incorrect associations. SSVS with an informed prior had a higher average per cent of correct associations and a lower average per cent of incorrect associations than the CI approach. This study shows that the Bayesian methods offer a way to use prior information to both increase power and decrease false-positive results when selecting factors to model complex disease risk.     

Scope of Knowledge About Zika Among Women in US–Mexico Border Communities

Maternal Zika virus infection (ZIKV) has serious health consequences for unborn offspring. Knowledge about prevention is critical to reducing risk, yet what women in the high-risk US–Mexico border region know about protecting themselves and their babies from ZIKV is mostly unknown. This study aimed to assess knowledge of ZIKV among pregnant and inter-conception women and to identify sources of information that might address knowledge gaps. Clients in five federally-funded, border region Healthy Start programs (N?=?326) were interviewed in late 2016 about their knowledge of ZIKV prevention methods and whether they believed themselves or their babies to be at risk. Sources of information about ZIKV and demographic characteristics were also measured. Chi square tests identified important associations between variables; adjusted odds ratios (AOR) and 95% confidence intervals for knowledge and beliefs were calculated. Among the 305 women aware of ZIKV, 69.5% could name two ways to prevent infection. Only 16.1% of women named using condoms or abstaining from sex as a prevention method. While 75.3% heard about ZIKV first from TV/radio, just 9.5% found the information helpful. Women who received helpful information from health care providers had greater odds of knowing two prevention methods (AOR?=?2.0; 1.1–3.7), when to test for ZIKV (AOR?=?5.2; 2.1–13.2), and how long to delay pregnancy after infection in a male partner (AOR?=?1.9; 1.1–3.2). Those who said web-based and social media sources were helpful had greater odds of knowing when to test for ZIKV (AOR?=?2.8; 1.3–6.3). Results can inform messaging for safe pregnancy and ZIKV prevention.     

Evaluating the risks of cesarean section: low Apgar score in repeat C-section and vaginal deliveries.

Data from Washington State birth certificates from 1980-83 were used to estimate excess risk to the infant delivered via repeat cesarean section independently of any risk associated with the indication for the procedure. Using a case-control design, we compared the method of delivery of all infants with low (0-6) five-minute Apgar scores born to multiparous mothers after uncomplicated pregnancies and births to that of similar infants with a high score (7-10), frequency matched by birthweight. Of the 1,030 infants with low Apgar score, 127 (12.3 per cent) were delivered via repeat cesarean section, in contrast to 98 (9.8 per cent) of 998 controls with high Apgar score. In a regression model controlling for birthweight, gestational length, maternal age, and income the relative risk was 1.29 (95% confidence interval 0.97, 1.72). Excess risk was highest among babies of normal (2500-4000 grams) birthweight. While a number of limitations inherent in the source of data require cautious interpretation of these results, we conclude that some excess risk of low Apgar score may be associated with repeat cesarean section procedures.     

Assessment of self-report in HIV surveillance: a pilot study

Abstract: The basis of HIV exposure category classification was investigated among selected cases of newly diagnosed HIV infection. Questionnaires seeking specific information on patient-reported exposure to HIV were forwarded to doctors who had requested the HIV antibody test for patients who met the study sample criteria. The cases of interest were those newly diagnosed between 1 January and 31 October 1991 and notified to state and territory health authorities as having been attributed to exposures to HIV other than male homosexual contact or receipt of blood, blood products or tissue. A total of 158 questionnaires was forwarded and 59 per cent were returned. Among the returned questionnaires included in the study sample, exposure to HIV on the original notification to the health authority was given as injecting drug use (8 per cent, 3 of 37), heterosexual contact (46 per cent, 17 of 37), or unavailable (46 per cent, 17 of 37). A clear basis for HIV exposure category classification was provided on the questionnaires for 70 per cent (7 of 10) of cases among women, whereas among men whose infection was attributed to heterosexual contact, a basis for exposure category classification was specified for only 43 per cent (10 of 23) of cases. Although the study was limited by the low response rate, use of the questionnaire provided a relatively simple means for assessing self-reported HIV exposure history.     

Jabs in the dark: injecting equipment found in prisons,and the risks of viral transmission

Abstract: Injecting drug users in prisons may reuse and share contaminated injecting equipment, increasing their risk of infection with blood-borne viruses. We examined 58 syringes found in three metropolitan Adelaide prisons during a one-year period: 95 per cent were one millilitre volume; blood was visible in 24 per cent; 58 per cent indicated repeated use; 33 per cent were wrapped in plastic; and 26 per cent had detachable needles, allowing more blood to be trapped in the dead space between the syringe barrel and needle than with the fixed-needle variety. The nature and condition of some of these syringes suggested they might transmit contaminated blood. The ineffectiveness of present approaches to keeping injecting equipment out of prisons demands a more enlightened approach to harm minimisation. With doubts cast on the efficacy of bleach, education should be supported by practical means to reduce transmission of viruses. Provision of sterile injecting equipment is a possible option.     

Association of obesity and ovarian cancer in a case-control study

Data from a population-based case-control study conducted in Washington State and Utah were used to assess whether obesity is associated with an altered risk of epithelial ovarian cancer. Quetelet index, defined as weight (kg) at age 30 years divided by height (m) squared, was calculated for each woman, and the values for all subjects were divided into five categories of approximately equal size. Compared with women in the lowest category, women in the highest category had an odds ratio of 1.7 (95 per cent CI 1.1-2.7). Risks for women in the three intermediate Quetelet index categories also exceeded the risk for women in the lowest group, but to a much smaller degree. Among women with serous tumors, those in the highest Quetelet index category were at a greater than twofold excess risk (OR = 2.2, 95 per cent CI 1.1-4.2), but the risk was not increased in the intermediate categories. For endometrioid tumors, risk increased consistently with increasing Quetelet index, and the odds ratio in the highest category was 4.7 (95 per cent CI 1.0-22.7). For both serous and endometrioid tumors, the excess risk was largely confined to premenopausal women. The results of this analysis suggest that for at least some types of ovarian tumor, obesity may warrant further attention as a possible etiologic factor.     

Estimation of infectious disease parameters from serological survey data: the impact of regular epidemics

Serological surveys are a useful source of information about epidemiological parameters for infectious diseases. In particular they may be used to estimate contact rates, forces of infection, the reproduction number and the critical vaccination threshold. However, these estimation methods require the assumption that the infection is in endemic equilibrium. Such equilibria seldom exist in practice: for example, many common infections of childhood exhibit regular epidemic cycles. In this paper, we investigate whether ignoring such cycles produces biased estimates. We apply the methods to data on mumps and rubella in the U.K. prior to the introduction of the combined measles, mumps, rubella (MMR) vaccine. We conclude that past epidemics have only a marginal effect on estimates, and that standard methods that do not adjust for regular epidemics are valid.     

An outbreak of cryptosporidiosis associated with an animal nursery at a regional fair.

Cryptosporidiosis is a common gastrointestinal illness that is transmitted from infected persons, animals, or contaminated water or food. This article reports on an outbreak of cryptosporidiosis associated with an animal nursery at an agricultural show held in northern Tasmania during October 2001. Eighty-one per cent of cases (38/47) notified to the Tasmanian Department of Health and Human Services over a 35 day period were interviewed to determine potential sources of infection. Eighty-one per cent of interviewed cases (29/36) reported that they had attended the agricultural show, and 75 per cent (27/36) reported contact with animals in the animal nursery. Cases occurring more than one incubation period after the agricultural show were significantly more likely to have had contact with someone else with diarrhoea (p<0.01). This is the first reported outbreak of cryptosporidiosis associated with an animal nursery in Australia. The outbreak demonstrates the importance of infection control policies and hygiene measures in the animal nursery setting.     

Knowledge of and attitudes to infection control of tattooists at registered premises in Victoria, 1994

Abstract: Historically, the relationship between health authorities and tattooists has been marked by suspicion and mutual distrust, with tattooists being stereotyped as having little concern for hygiene, and considered largely ineducable about infection control. In this study, a random sample of tattooists working at one–third of the 65 registered tattooing premises in Victoria completed a questionnaire that recorded demographic information and knowledge and attitudes to Standards of practice for tattooing 1990, which specifies guidelines for infection control in Victorian tattooing premises. Of these premises, 89 per cent participated and 36 of 37 tattooists working therein (22 metropolitan, 14 country) completed the questionnaire; 81 per cent were male. Reports by the tattooists indicated that: 50 per cent had not commenced immunisation for hepatitis B; that 78, 42 and 34 per cent either had not been tested or were unsure whether they had been tested for hepatitis C, hepatitis B and human immunodeficiency virus (HIV); and that no tattooist was a hepatitis B carrier or was positive for hepatitis C or HIV. Respondents acknowledged the potential for transmission of infectious diseases through tattooing, endorsed formal training in tattooing and infection control for new tattooists, and supported continuing education in infection control for existing tattooists. Most were critical of environmental health officers, particularly for inaction in not closing and prosecuting unregistered tattooists. Despite deficiencies in the knowledge and training of tattooists in infection control, they recognise its importance and are willing to attend appropriate training.     

Urinary-tract infection and bacteraemia in hospitalized medical patients--a European multicentre prevalence survey on nosocomial infection

A co-ordinated survey of 3899 medical patients in 169 wards, performed simultaneously in eight countries, showed a point-prevalence of urinary-tract infection (UTI) and bacteraemia of 12.6 and 1.6 per cent, respectively. One-half of the infections were acquired after the patients' admission. The bacteriological patterns of hospital- vs community-acquired infections were different, but showed no unexpected features. Antibiotic treatment was recorded in 22.3 per cent of the patients in this study, urinary-tract disinfectants, sulphonamides or penicillins being used in 95 per cent of those treated for UTI. The overall prevalence of urinary-tract drainage was 11.0 per cent with no significant difference between the two sexes. At ward level the rate of catheterized patients varied from below 5 per cent to more than 25 per cent, indicating--besides variations in the ward populations--differences in policies. The association between nosocomial UTI and the presence of an indwelling catheter and/or female sex was confirmed, while high age appeared to be a secondary risk factor among catheterized patients. The prevalence of nosocomial bacteraemia in patients with UTI was five times higher than in those without urinary-tract involvement, and a significant part of the nosocomial cases of both UTI and bacteraemia was clearly device-related. Guidelines for the use of indwelling catheters should be restrictive and provide for prompt removal. When introduced and followed they will effectively reduce nosocomial UTI and bacteraemia.