Approximating posteriors with high-dimensional nuisance parameters via integrated rotated Gaussian approximation.

Posterior computation for high-dimensional data with many parameters can be challenging. This article focuses on a new method for approximating posterior distributions of a low- to moderate-dimensional parameter in the presence of a high-dimensional or otherwise computationally challenging nuisance parameter. The focus is on regression models and the key idea is to separate the likelihood into two components through a rotation. One component involves only the nuisance parameters, which can then be integrated out using a novel type of Gaussian approximation. We provide theory on approximation accuracy that holds for a broad class of forms of the nuisance component and priors. Applying our method to simulated and real data sets shows that it can outperform state-of-the-art posterior approximation approaches.

Is rectal douching and sharing douching equipment associated with anorectal chlamydia and gonorrhoea? A cross-sectional study among men who have sex with men.

INTRODUCTION: Men who have sex with men (MSM) are at high risk for anorectal chlamydia and gonorrhoea infections. Many MSM use rectal douches in preparation for sex, which might break down the mucosal barrier function and facilitate the acquisition of STI. We determined whether rectal douching or sharing douching equipment was associated with anorectal chlamydia and gonorrhoea. METHODS: In a cross-sectional study among 994 MSM attending the STI outpatient clinic of Amsterdam between February and April 2011, data were collected on rectal douching, sexual behaviour and STI. We used multivariable logistic regression analysis to determine the association between rectal douching, including sharing of douching equipment, and anorectal chlamydia and gonorrhoea for those reporting receptive anal sex. We adjusted for other risk behaviour, that is, condom use, number of partners and HIV status. RESULTS: Of 994 MSM, 46% (n=460) practised rectal douching, of whom 25% (n=117) shared douching equipment. Median age was 39 years (IQR 30-47), median number of sex partners in the 6 months prior to consult was five (IQR 3-10) and 289 (29.0%) participants were HIV positive. The prevalence of anorectal chlamydia and/or gonorrhoea for those reporting receptive anal sex was 9.6% (n=96). In multivariable analysis, HIV positivity (aOR=2.2, 95% CI 1.3 to 3.6), younger age (aOR=2.5, CI 1.4 to 4.5 for those aged <35 years compared with those aged ≥45 years), and more sexual partners (aOR=1.2, 95% CI 1.0 to 1.5 for 1 log increase) were significantly associated with anorectal STI. However, rectal douching or sharing douching equipment were not significantly associated with anorectal chlamydia and/or gonorrhoea (p=0.647). CONCLUSIONS: Almost half of MSM used rectal douching and a quarter of these shared douching equipment. Though using douching equipment does not appear to contribute to anorectal chlamydia and gonorrhoea in this study, STI prevalence remains high and prevention strategies like early testing and treatment remain of utmost importance.