Cross-sectional Prevalence Data Research Articles

Joint Modeling of HCV and HIV Infections among Injecting Drug Users in Italy Using Repeated Cross-Sectional Prevalence Data

During their injecting career, injecting drug users (IDUs) are exposed to some infections, like hepatitis C virus (HCV) infection and human immunodeficiency virus (HIV) infection, due to their injecting behavioral risk factors, such as sharing syringes or other paraphernalia containing infected blood, or sexual behavior risk factors. If we consider that these IDUs might belong to a social network of people where these behavioral risk factors are spread, then HCV and HIV infections might be associated at both the individual and the population level. In this paper, we study the association between HCV and HIV infection at the population level using aggregate data. Our aim is to define a hierarchy of structured models with which the association between HCV and HIV infection at population level and the time trend of prevalence can be investigated. The data analyzed in the paper are “diagnostic testing data,” which consist of repeated cross-sectional prevalence measurements from 1998 to 2006 for HCV and HIV infection, obtained from a sample of 515 drug treatment centers spread among the 20 regions in Italy, where subjects went for a serum diagnostic test. Since we do not have any individual data, it is not possible to relate these prevalence data to socio-demographic or behavioral risk data. Each region defines a cluster with repeated prevalence data for HCV and HIV infection over time. Several modeling approaches, such as generalized linear mixed models (GLMMs) and hierarchical Bayesian models are applied to the data. First, we test different covariance structures for the region-specific random effects in the GLMM context; second, a hierarchical Bayesian model is used to refit the best GLMM in order to obtain the posterior distribution for the parameters of primary interest. We found that the correlation at population level between HCV and HIV is approximately 0.68 and the prevalence of the two infections generally decreased over the years, compared to the situation in 1998.

Obtaining multistate life table distributions for highly refined subpopulations from cross-sectional data: A bayesian extension of sullivan’s method

Multistate life table methods are often used to estimate the proportion of remaining life that individuals can expect to spend in various states, such as healthy and unhealthy states. Sullivan's method is commonly used when panels containing data on transitions are unavailable and true multistate tables cannot be generated. Sullivan's method requires only cross-sectional mortality data and cross-sectional data indicating prevalence in states of interest. Such data often come from sample surveys, which are widely available. Although the data requirements for Sullivan's method are minimal, the method is limited in its ability to produce estimates for subpopulations because of limited disaggregation of data in cross-sectional mortality files and small cell sizes in aggregated survey data. In this article, we develop, test, and demonstrate a method that adapts Sullivan's approach to allow the inclusion of covariates in producing interval estimates of state expectancies for any desired subpopulation that can be specified in the cross-sectional prevalence data. The method involves a three-step process: (1) using Gibbs sampling to sample parameters from a bivariate regression model; (2) using ecological inference for producing transition probability matrices from the Gibbs samples; (3) using standard multistate calculations to convert the transition probability matrices into multistate life tables.

Recovering incidence from repeated measures of prevalence: the case of urinary tract infections

To study the relationships between prevalence and incidence in the case of nosocomial infections of the urinary tract, and to evaluate if repeated prevalence measures may be useful to obtain an estimate of incidence. Methodology is based on a simple and reasonable assumption on the infection dynamics: starting from a difference equation modeling the evolution of hospital population, it is obtained a set of equations allowing to calculate the incidence by means of the knowledge of prevalence. The numerical validation of the model done by computer simulations, shows that the model obtains a better estimate of incidence than the approach given by the classical rule prevalence = incidence x duration. The proposed strategy permits to forecast the incidence of the urinary tract nosocomial infections by using repeated measures of prevalence. It is hence possible to estimate the incidence from cross-sectional prevalence data with sufficient accuracy to monitor and estimate the time dynamics of these infections.

The association between graded physical activity in postmenopausal British women, and the prevalence and incidence of hip and wrist fractures

physical activity is promoted for older women as a means of maintaining health and avoiding falls and fractures. Findings relating physical activity of older women to risk of falls and fracture are contradictory. The association between level of physical activity and prevalent and incident hip and wrist fractures was examined in a large representative sample of postmenopausal British women. data from the British Women's Heart and Health Study, a cohort study of 4286 postmenopausal women aged 60-79, from 23 UK towns were used. Information on physical activity, anthropometry, falls and hip and wrist fractures from baseline examination and questionnaire (1999-2001) and follow-up questionnaire (2007) were available. Cross-sectional baseline prevalence data were analysed using logistic regression and cohort incidence data using a Cox proportional hazards model examining the association of physical activity with fracture outcomes. 3003 (70%) women, with complete baseline data, were studied. 13.6% had previously fractured a wrist and 1.3% a hip. Analyses unadjusted for confounders showed moderate protective associations between activity and fracture risk. After adjustment for confounders there was a weak trend towards fewer hip fractures (adjusted OR 0.13 [0.01, 1.18]) and more wrist fractures (adjusted OR 1.35 [0.76, 2.48]), amongst most active compared with inactive women. The crude incidence rate of wrist and/or hip fracture was 7.0 [5.9, 8.2] per 1000 person-years. No evidence was found for an association between physical activity and combined incident hip and/or wrist fracture (adjusted rate ratio inactive versus most active 1.69 [0.67, 4.24]). no clear associations between graded physical activity and hip/wrist fractures were seen but estimates were imprecise. Physical activities are heterogeneous and individual fracture types and mechanisms differ. Very large prospective observational studies are required to disentangle the precise effects of different activity patterns on different fracture types.

The association between graded physical activity in postmenopausal British women and the prevalence and incidence of hip and wrist fractures

Background physical activity is promoted for older women as a means of maintaining health and avoiding falls and fractures. Findings relating physical activity of older women to risk of falls and fracture are contradictory. The association between level of physical activity and prevalent and incident hip and wrist fractures was examined in a large representative sample of postmenopausal British women. Methods data from the British Women's Heart and Health Study, a cohort study of 4286 postmenopausal women aged 60-79, from 23 UK towns were used. Information on physical activity, anthropometry, falls and hip and wrist fractures from baseline examination and questionnaire (1999-2001) and follow-up questionnaire (2007) were available. Cross-sectional baseline prevalence data were analysed using logistic regression and cohort incidence data using a Cox proportional hazards model examining the association of physical activity with fracture outcomes. Results 3003 (70%) women, with complete baseline data, were studied. 13.6% had previously fractured a wrist and 1.3% a hip. Analyses unadjusted for confounders showed moderate protective associations between activity and fracture risk. After adjustment for confounders there was a weak trend towards fewer hip fractures (adjusted OR 0.13 [0.01, 1.18]) and more wrist fractures (adjusted OR 1.35 [0.76, 2.48]), amongst most active compared with inactive women. The crude incidence rate of wrist and/or hip fracture was 7.0 [5.9, 8.2] per 1000 person-years. No evidence was found for an association between physical activity and combined incident hip and/or wrist fracture (adjusted rate ratio inactive versus most active 1.69 [0.67, 4.24]). Conclusion no clear associations between graded physical activity and hip/wrist fractures were seen but estimates were imprecise. Physical activities are heterogeneous and individual fracture types and mechanisms differ. Very large prospective observational studies are required to disentangle the precise effects of different activity patterns on different fracture types.

Alcohol and transactional sex: How risky is the mix?

This study examines alcohol use, transactional sex (TS), and sexually transmitted infection (STI) risk among sugar plantation residents near Moshi, Tanzania, from 2002 to 2004. We compare popular discourse gathered through ethnographic methods with cross-sectional questionnaire and STI prevalence data to illuminate the close correspondence of alcohol use and TS with STI transmission. People attributed to alcohol varied consequences: some socially desirable (relaxing, reducing worries) and others (drunkenness, removing shame) thought to put alcohol abusers at risk for STIs. TS-exchanging money, food, gifts, alcohol or work for sex-was not stigmatized, but people believed that seeking sexual partners for money (or providing money to sexual partners) led to riskier sexual relationships. We explore popular discourse about how alcohol use and TS independently and in combination led to increased STI exposure. Popular discourse blamed structural circumstances-limited economic opportunities, few social activities, separated families-for risky sex and STIs. To understand individual behavior and risk, we surveyed 556 people. We measured associations between their self-reported behaviors and infection with herpes simplex virus type-2 (HSV-2), syphilis, and HIV in 462 participants who were tested. Alcohol abuse was associated with prevalent STI and HIV infection. Exchanging sex for alcohol and work were both associated with prevalent STI. Participants who both abused alcohol and participated in TS had greatest risk for STI. Findings from the two analytic methods-interrogation of popular discourse, and association between self-reported behavior and STIs-were largely in agreement. We posit explanations for discrepancies we found through the concepts of sensationalization, self-exceptionalization, and the influence of an authoritative moral discourse.

MYCOBACTERIOSIS‐ASSOCIATED MORTALITY IN WILD STRIPED BASS (MORONE SAXATILIS) FROM CHESAPEAKE BAY, USA

The striped bass (Morone saxatilis) is an economically and ecologically important finfish species along the Atlantic seaboard of the United States. Recent stock assessments in Chesapeake Bay (U.S.A.) indicate that non-fishing mortality in striped bass has increased since 1999, concomitant with very high (>50%) prevalence of visceral and dermal disease caused by Mycobacterium spp. Current fishery assessment models do not differentiate between disease and other components of non-fishing mortality (e.g., senescence, predation); therefore, disease impact on the striped bass population has not been established. Specific measurement of mortality associated with mycobacteriosis in wild striped bass is complicated because the disease is chronic and mortality is cryptic. Epidemiological models have been developed to estimate disease-associated mortality from cross-sectional prevalence data and have recently been generalized to represent disease processes more realistically. Here, we used this generalized approach to demonstrate disease-associated mortality in striped bass from Chesapeake Bay. To our knowledge this is the first demonstration of cryptic mortality associated with a chronic infectious disease in a wild finfish. This finding has direct implications for management and stock assessment of striped bass, as it demonstrates population-level negative impacts of a chronic disease. Additionally, this research provides a framework by which disease-associated mortality may be specifically addressed within fisheries models for resource management.

Estimating Incidence from Prevalence in Generalised HIV Epidemics: Methods and Validation

BackgroundHIV surveillance of generalised epidemics in Africa primarily relies on prevalence at antenatal clinics, but estimates of incidence in the general population would be more useful. Repeated cross-sectional measures of HIV prevalence are now becoming available for general populations in many countries, and we aim to develop and validate methods that use these data to estimate HIV incidence.Methods and FindingsTwo methods were developed that decompose observed changes in prevalence between two serosurveys into the contributions of new infections and mortality. Method 1 uses cohort mortality rates, and method 2 uses information on survival after infection. The performance of these two methods was assessed using simulated data from a mathematical model and actual data from three community-based cohort studies in Africa. Comparison with simulated data indicated that these methods can accurately estimates incidence rates and changes in incidence in a variety of epidemic conditions. Method 1 is simple to implement but relies on locally appropriate mortality data, whilst method 2 can make use of the same survival distribution in a wide range of scenarios. The estimates from both methods are within the 95% confidence intervals of almost all actual measurements of HIV incidence in adults and young people, and the patterns of incidence over age are correctly captured.ConclusionsIt is possible to estimate incidence from cross-sectional prevalence data with sufficient accuracy to monitor the HIV epidemic. Although these methods will theoretically work in any context, we have able to test them only in southern and eastern Africa, where HIV epidemics are mature and generalised. The choice of method will depend on the local availability of HIV mortality data.

Estimating HIV hazard rates from cross-sectional HIV prevalence data

We propose a method of estimating the HIV hazard rate in a population when only cross-sectional data measuring HIV-prevalence are available. In a cross-sectional study, individuals who test positive are left-censored since we know only that the transition time is smaller than the monitoring time. Individuals who test negative are right-censored since we know only that the transition time is greater than the monitoring time. The transition time is not observed directly. For our method, we assume the hazard rate is well-defined after the time we start screening. We assume further the mortality rates for HIV-positive and HIV-negative individuals are known. The method is illustrated using HIV-prevalence data collected over four years among women in Cape Town, South Africa.

Panic Attacks and Suicide Attempts

To the Editor.— Weissman et al 1 and Johnson et al 2 reported cross-sectional survey results from the National Institute of Mental Health Epidemiologic Catchment Area Program to show that a history of panic attacks signaled a markedly high lifetime prevalence of suicide attempts, even in the absence of other diagnosed psychiatric disorders. On this basis, the authors argued that physicians should be attentive to panic symptoms shown in their patients. We were concerned that reliance on cross-sectional lifetime prevalence data might create a spurious artifact in the form of an association between a history of panic attacks and a history of suicide attempts. For this reason, we extended a prior casecontrol analysis based on 40 community survey respondents who recently attempted suicide and 160 matched controls. 3 The recent suicide attempters were detected at cross-section and at follow-up after 1 year in the prospective component of the Epidemiologic Catchment