A comparison of missing data procedures for addressing selection bias in HIV sentinel surveillance data

Background

Selection bias is common in clinic-based HIV surveillance. Clinics located in HIV hotspots are often the first to be chosen and monitored, while clinics in less prevalent areas are added to the surveillance system later on. Consequently, the estimated HIV prevalence based on clinic data is substantially distorted, with markedly higher HIV prevalence in the earlier periods and trends that reveal much more dramatic declines than actually occur.

Methods

Using simulations, we compare and contrast the performance of the various approaches and models for handling selection bias in clinic-based HIV surveillance. In particular, we compare the application of complete-case analysis and multiple imputation (MI). Several models are considered for each of the approaches. We demonstrate the application of the methods through sentinel surveillance data collected between 2002 and 2008 from India.

Results

Simulations suggested that selection bias, if not handled properly, can lead to biased estimates of HIV prevalence trends and inaccurate evaluation of program impact. Complete-case analysis and MI differed considerably in their ability to handle selection bias. In scenarios where HIV prevalence remained constant over time (i.e. β = 0), the estimated ${\widehat{\beta }}_1$ derived from MI tended to be biased downward. Depending on the imputation model used, the estimated bias ranged from ?1.883 to ?0.048 in logit prevalence. Furthermore, as the level of selection bias intensified, the extent of bias also increased. In contrast, the estimates yielded by complete-case analysis were relatively unbiased and stable across the various scenarios. The estimated bias ranged from ?0.002 to 0.002 in logit prevalence.

Conclusions

Given that selection bias is common in clinic-based HIV surveillance, when analyzing data from such sources appropriate adjustment methods need to be applied. The results in this paper suggest that indiscriminant application of imputation models can lead to biased results.

     

HDL and endothelial protection

High-density lipoproteins (HDLs) represent a family of particles characterized by the presence of apolipoprotein A-I (apoA-I) and by their ability to transport cholesterol from peripheral tissues back to the liver. In addition to this function, HDLs display pleiotropic effects including antioxidant, anti-apoptotic, anti-inflammatory, anti-thrombotic or anti-proteolytic properties that account for their protective action on endothelial cells. Vasodilatation via production of nitric oxide is also a hallmark of HDL action on endothelial cells. Endothelial cells express receptors for apoA-I and HDLs that mediate intracellular signalling and potentially participate in the internalization of these particles. In this review, we will detail the different effects of HDLs on the endothelium in normal and pathological conditions with a particular focus on the potential use of HDL therapy to restore endothelial function and integrity.     

A 15q13.3 microdeletion segregating with autism

Autism and mental retardation (MR) show high rates of comorbidity and potentially share genetic risk factors. In this study, a rare ∼2 Mb microdeletion involving chromosome band 15q13.3 was detected in a multiplex autism family. This genomic loss lies between distal break points of the Prader–Willi/Angelman syndrome locus and was first described in association with MR and epilepsy. Together with recent studies that have also implicated this genomic imbalance in schizophrenia, our data indicate that this CNV shows considerable phenotypic variability. Further studies should aim to characterise the precise phenotypic range of this CNV and may lead to the discovery of genetic or environmental modifiers.     

老年急性心肌梗死急诊PCI术后联合服用尼可地尔与曲美他嗪对改善心功能的短期随访研究

目的：观察急诊经皮冠状动脉介入术(PCI)后联合服用尼可地尔、曲美他嗪对对老年多支病变ST段抬高型心肌梗死(STEMI)心功能的改善效果。方法：将2014年6月-2016年12月期间105例急诊PCI有效病例据随机数字分为观察组(52例)、对照组(53例),对照组出院后服用盐酸曲美他嗪片,每次20mg,每日3次,连服6个月,观察组在对照组基础上加服尼可地尔片,每次5mg,每日3次,术后随访6个月,比较两组血清学心肌损伤标志物、顿抑心肌血流灌注、心功能及不良心血管事件。结果：两组术后6个月BNP、Hs-CRP、MMP-9均显著低于本组术后3个月水平(P<0.05);术后3个月,观察组BNP(202.7±42.6 vs. 225.7±48.3) pg/ml显著低于对照组(P<0.05),术后6个月观察组BNP(137.9±36.5 vs. 165.9±41.1) pg/ml、Hs-CRP(4.19±1.23 vs. 5.01±1.55) mg/L、MMP-9(82.8±13.6 vs. 95.7±17.4) μg/L均显著低于对照组(P<0.05)。心肌核素显像显示两组术后6个月SRS、TPD%均显著低于术后3个月水平(P<0.05);术后3个月观察组SRS(15.6±3.8 vs. 17.9±4.3)显著低于对照组,术后6个月观察组SRS(8.9±2.3 vs. 13.5±2.8)、TPD%(18.2±4.9 vs. 22.4±5.7)%均显著低于对照组(P<0.05)。超声心动图检查显示两组术后LVEF、PER均较出院前显著提高(P<0.05),LVESVI、LVEDVI均显著降低(P<0.05);术后3个月观察组LVEF(56.1±4.5 vs. 53.9±4.6)%显著高于对照组,术后6个月观察组LVEF(58.8±4.7 vs. 56.5±4.7)%、PER(1.82±0.13 vs. 1.77±0.11) EDV/s均显著高于对照组(P<0.05),而LVESVI(38.5±6.3 vs. 42.1±7.8) ml/m₂、LVEDVI(85.6±12.5 vs. 92.4±14.4)ml/m₂均显著低于对照组水平(P<0.05)。观察组随访期内心绞痛发生率(7.7% vs.17.0%)、靶血管血运重建比例(1.9% vs.5.7%)、再入院比例(5.8% vs.9.4%)低于对照组,差异均无统计学意义(P＞0.05)。结论：尼可地尔、曲美他嗪对改善心肌灌注作用协同,急诊PCI术后口服曲美他嗪基础上加服尼可地尔有助于减轻心肌损伤,提高心功能,联合用药长期效果更为显著。     

Recurrent postoperative sciatica: evaluation with MR imaging and enhanced CT

Magnetic resonance (MR) imaging and computed tomography enhanced with intravenous iodine injection (ECT) were prospectively compared in 80 patients in the diagnosis of recurrent postoperative sciatica. Diagnostic accuracy was determined with surgical verification. Isolated fibrosis was considered a contraindication to surgery. A decision to operate was made in 56 of the 80 patients on the basis of MR imaging findings; in 21 of the 56, the decision was also made on the basis of ECT findings. Of the 80 patients, 45 underwent surgery, In all but one of these patients, the diagnosis made on the basis of MR imaging findings was confirmed with surgical analysis. The only surgical finding that did not agree with MR imaging findings was a calcification of the common posterior ligament. The 21 diagnoses of disk herniation based on ECT findings were confirmed surgically, but among the 24 diagnoses of fibrosis made with the help of ECT, there were actually 19 recurrent herniations, four herniations with fibrosis, and one herniation at the level above the previously resected disk. MR imaging seems to be the investigation of choice in diagnosing the cause of recurrent postoperative sciatica.