Closing the gap on causal processes of infection risk from cross-sectional data: structural equation models to understand infection and co-infection.

BACKGROUND: Epidemiological studies of disease exposure risk are frequently based on observational, cross-sectional data, and use statistical approaches as crucial tools for formalising causal processes and making predictions of exposure risks. However, an acknowledged limitation of traditional models is that the inferred relationships are correlational, cannot easily distinguish direct from indirect determinants of disease risk, and are often considerable simplifications of complex interrelationships. This may be particularly important when attempting to infer causality in patterns of co-infection through pathogen-facilitation. METHODS: We describe analyses of cross-sectional data using structural equation models (SEMs), a contemporary advancement on traditional regression approaches, based on our study system of feline gammaherpesvirus (FcaGHV1) in domestic cats. RESULTS: SEMs strongly supported a latent (host phenotype) variable associated with FcaGHV1 exposure and co-infection risk, suggesting these individuals are simply more likely to become infected with multiple pathogens. However, indications of pathogen-covariance (potential facilitation) were also variably detected: potentially among FcaGHV1, Bartonella spp and Mycoplasma spp. CONCLUSIONS: Our models suggest multiple exposures are primarily driven by host phenotypic traits, such as aggressive male phenotypes, and secondarily by pathogen-pathogen interactions. The results of this study demonstrate the application of SEMs to understanding epidemiological processes using observational data, and could be used more widely as a complementary tool to understand complex cross-sectional information in a wide variety of disciplines.

Felis catus gammaherpesvirus 1; a widely endemic potential pathogen of domestic cats.

Felis catus gammaherpesvirus 1 (FcaGHV1), recently discovered in the USA, was detected in domestic cats in Australia (11.4%, 95% confidence interval 5.9-19.1, n=110) and Singapore (9.6%, 95% confidence interval 5.9-14.6, n=176) using qPCR. FcaGHV1 qPCR positive cats were 2.8 times more likely to be sick than healthy. Risk factors for FcaGHV1 detection included being male, increasing age and coinfection with pathogenic retroviruses, feline immunodeficiency virus (FIV) or feline leukaemia virus. FcaGHV1 DNA was detected in multiple tissues from infected cats with consistently high virus loads in the small intestine. FcaGHV1 viral load was significantly higher in FIV-infected cats compared with matched controls, mimicking increased Epstein-Barr virus loads in human immunodeficiency virus-infected humans. FcaGHV1 is endemic in distant geographic regions and is associated with being sick and with coinfections. Horizontal transmission of FcaGHV1 is supported, with biting being a plausible route. A pathogenic role for FcaGHV1 in domestic cats is supported.

General practice and social service partnership for better clinical outcomes, patient self efficacy and lifestyle behaviours of diabetic care: randomised control trial of a chronic care model.

BACKGROUND: The International Diabetes Attitudes, Wishes, and Needs (DAWN) programmes have shown the existence of a critical gap in self management support and access to the support system. This study aims to evaluate the effectiveness of the diabetes mellitus (DM) self management programme, with partnership between general practice and social work, on clinical outcomes, patient self efficacy and lifestyle behaviours. METHODS: In this is single blind randomised controlled trial, subjects were recruited from patients attending general outpatient clinics in the Hospital Authority New Territory East Cluster of Hong Kong. 157 subjects meeting the inclusion criteria completed the study and were randomly assigned to the experimental or control group. The experimental group underwent the six sessions of weekly DM self management course with emphasis on self efficacy and participatory approach. The outcome measurements included HbA1c concentration, DM self efficacy scale, dietary behaviours, body mass index (BMI), and waist: hip ratio. RESULTS: Baseline assessment observed no significant differences between experimental and control groups for the variables related to outcomes. For the experimental group, the proportion of subjects with normal HbA1c increased from 4.5% (3/66) at baseline to 28.6% (19/66) at week 28 (p<0.001), but there was insignificant improvement in the control group (3.9% to 11.8%, p=0.13). Repeated measure of analysis of variance showed pronounced improvement in DM self efficacy scale and BMI among the experimental group with significant interaction. Dietary behaviours also improved significantly in the experimental group. CONCLUSION: The DM care model with partnership between general practice and social work demonstrated better diabetic control with improvement of self efficacy and minimisation of risk behaviours. TRIAL REGISTRATION: Current Controlled Trials ISRCTN78882965.