Simplifying the estimation of diagnostic testing accuracy over time for high specificity tests in the absence of a gold standard.

Many different methods for evaluating diagnostic test results in the absence of a gold standard have been proposed. In this paper, we discuss how one common method, a maximum likelihood estimate for a latent class model found via the Expectation-Maximization (EM) algorithm can be applied to longitudinal data where test sensitivity changes over time. We also propose two simplified and nonparametric methods which use data-based indicator variables for disease status and compare their accuracy to the maximum likelihood estimation (MLE) results. We find that with high specificity tests, the performance of simpler approximations may be just as high as the MLE.

Identifying Paucisymptomatic or Asymptomatic and Unrecognized Ebola Virus Disease Among Close Contacts Based on Exposure Risk Assessments and Screening Algorithms.

BACKGROUND: There is limited evidence to evaluate screening algorithms with rapid antigen testing and exposure assessments as identification strategies for paucisymptomatic or asymptomatic Ebola virus (EBOV) infection and unrecognized EBOV disease (EVD). METHODS: We used serostatus and self-reported postexposure symptoms from a cohort study to classify contact-participants as having no infection, paucisymptomatic or asymptomatic infection, or unrecognized EVD. Exposure risk was categorized as low, intermediate, or high. We created hypothetical scenarios to evaluate the World Health Organization (WHO) case definition with or without rapid diagnostic testing (RDT) or exposure assessments. RESULTS: This analysis included 990 EVD survivors and 1909 contacts, of whom 115 (6%) had paucisymptomatic or asymptomatic EBOV infection, 107 (6%) had unrecognized EVD, and 1687 (88%) were uninfected. High-risk exposures were drivers of unrecognized EVD (adjusted odds ratio, 3.5 [95% confidence interval, 2.4-4.9]). To identify contacts with unrecognized EVD who test negative by the WHO case definition, the sensitivity was 96% with RDT (95% confidence interval, 91%-99%), 87% with high-risk exposure (82%-92%), and 97% with intermediate- to high-risk exposures (93%-99%). The proportion of false-positives was 2% with RDT and 53%-93% with intermediate- and/or high-risk exposures. CONCLUSION: We demonstrated the utility and trade-offs of sequential screening algorithms with RDT or exposure risk assessments as identification strategies for contacts with unrecognized EVD.

Triangulating Evidence to Infer Pathways that Influence Ebola Virus Disease-Related Stigma and Clinical Findings among Survivors: An Observational Cohort Study.

Visible signs of disease can evoke stigma while stigma contributes to depression and mental illness, sometimes manifesting as somatic symptoms. We assessed these hypotheses among Ebola virus disease (EVD) survivors, some of whom experienced clinical sequelae. Ebola virus disease survivors in Liberia were enrolled in an observational cohort study starting in June 2015 with visits every 6 months. At baseline and 18 months later, a seven-item index of EVD-related stigma was administered. Clinical findings (self-reported symptoms and abnormal findings) were obtained at each visit. We applied the generalized estimating equation method to assess the bidirectional concurrent and lagged associations between clinical findings and stigma, adjusting for age, gender, educational level, referral to medical care, and HIV serostatus as confounders. When assessing the contribution of stigma to later clinical findings, we restricted clinical findings to five that were also considered somatic symptoms. Data were obtained from 859 EVD survivors. In concurrent longitudinal analyses, each additional clinical finding increased the adjusted odds of stigma by 18% (95% CI: 1.11, 1.25), particularly palpitations, muscle pain, joint pain, urinary frequency, and memory loss. In lagged associations, memory loss (adjusted odds ratio [AOR]: 4.6; 95% CI: 1.73, 12.36) and anorexia (AOR: 4.17; 95% CI: 1.82, 9.53) were associated with later stigma, but stigma was not significantly associated with later clinical findings. Stigma was associated with select symptoms, not abnormal objective findings. Lagged associations between symptoms and later stigma substantiate the possibility of a pathway related to visible symptoms identified by community members and leading to fear of contagion.

Ebola virus disease-related stigma among survivors declined in Liberia over an 18-month, post-outbreak period: An observational cohort study.

BACKGROUND: While qualitative assessments of Ebola virus disease (EVD)-related stigma have been undertaken among survivors and the general public, quantitative tools and assessment targeting survivors have been lacking. METHODS AND FINDINGS: Beginning in June 2015, EVD survivors from seven Liberian counties, where most of the country's EVD cases occurred, were eligible to enroll in a longitudinal cohort. Seven stigma questions were adapted from the People Living with HIV Stigma Index and asked to EVD survivors over the age of 12 at initial visit (median 358 days post-EVD) and 18 months later. Primary outcome was a 7-item EVD-related stigma index. Explanatory variables included age, gender, educational level, pregnancy status, post-EVD hospitalization, referred to medical care and EVD source. Proportional odds logistic regression models and generalized linear mixed-effects models were used to assess stigma at initial visit and over time. The stigma questions were administered to 859 EVD survivors at initial visit and 741 (86%) survivors at follow-up. While 63% of survivors reported any stigma at initial visit, only 5% reported any stigma at follow-up. Over the 18-month period, there was a significant decrease in stigma among EVD survivors (Adjusted Odds Ratio [AOR], 0.02; 95% Confidence Interval [CI], 0.01-0.04). At initial visit, having primary, junior high or vocational education, and being referred to medical care was associated with higher odds of stigma (educational level: AOR, 1.82; 95%CI, 1.27-2.62; referred: AOR, 1.50; 95%CI, 1.16-1.94). Compared to ages of 20-29, those who had ages of 12-19 or 50+ experienced lower odds of stigma (12-19: AOR, 0.32; 95%CI, 0.21-0.48; 50+: AOR, 0.58 95%CI, 0.37-0.91). CONCLUSIONS: Our data suggest that EVD-related stigma was much lower more than a year after active Ebola transmission ended in Liberia. Among survivors who screened negative for stigma, additional probing may be considered based on age, education, and referral to care.