Prevalence Threshold and Temporal Interpretation of Screening Tests: The Example of the SARS-CoV-2 (COVID-19) Pandemic

The curvilinear relationship between a screening tests positive predictive value (PPV) and its target disease prevalence is proportional. In consequence, there is an inflection point of maximum curvature in the screening curve defined as a function of the sensitivity (a) and specificity (b) beyond which the rate of change of a tests PPV declines sharply relative to disease prevalence ({phi}). Herein, we demonstrate a mathematical model exploring this phenomenon and define the prevalence threshold point ({phi}e) where this change occurs as: O_FD O_INLINEFIG[Formula]C_INLINEFIGC_FD Understanding where this prevalence point lies in the curve has important implications for the interpretation of test results, the administration of healthcare systems, the implementation of public health measures, and in cases of pandemics like SARS-CoV-2, the functioning of society at large. To illustrate the methods herein described, we provide the example of the screening strategies used in the SARS-CoV-2 (COVID-19) pandemic, and calculate the prevalence threshold statistic of different tests available today. This concept can help contextualize the validity of a screening test in real time, thereby enhancing our understanding of the dynamics of the current pandemic.

Rojiroti microfinance and child nutrition: a cluster randomised trial.

OBJECTIVE: To determine whether Rojiroti microfinance, for poor Indian women, improves child nutrition. DESIGN: Cluster randomised trial. SETTING: Tolas (village communities) in Bihar State. PARTICIPANTS: Women and children under 5 years. INTERVENTIONS: With Rojiroti microfinance, women form self-help groups and save their money to provide loans to group members. After 6 months, they receive larger external loans. Tolas were randomised to receive Rojiroti immediately or after 18 months. OUTCOME MEASURES: The primary analysis compared the mean weight for height Z score (WHZ) of children under 5 years in the intervention versus control tolas who attended for weight and height measurement 18 months after randomisation. Secondary outcomes were weight for age Z score (WAZ), height for age Z score, mid-upper arm circumference (MUAC), wasting, underweight and stunting. RESULTS: We randomised 28 tolas to each arm and collected data from 2469 children (1560 mothers) at baseline and 2064 children (1326 mothers) at follow-up. WHZ was calculated for 1718 children at baseline and 1377 (674 intervention and 703 control) at follow-up. At 18 months, mean WHZ was significantly higher for intervention (-1.02) versus controls (-1.37; regression coefficient adjusted for clustering ß=0.38, 95% CI 0.16 to 0.61, p=0.001). Significantly fewer children were wasted in the intervention group (122, 18%) versus control (200, 29%; OR=0.46, 95% CI 0.28 to 0.74, p=0.002). Mean WAZ was better in the intervention group (-2.13 vs -2.37; ß=0.27, 95% CI 0.11 to 0.43, p=0.001) as was MUAC (13.6 cm vs 13.4 cm; ß=0.22, 95% CI 0.03 to 0.40, p=0.02). In an analysis adjusting for baseline nutritional measures (259 intervention children and 300 control), only WAZ and % underweight showed significant differences in favour of the intervention. CONCLUSION: In marginalised communities in rural India, child nutrition was better in those who received Rojiroti microfinance, compared with controls. TRIAL REGISTRATION NUMBER: NCT01845545.

Feasibility and pilot study of the effects of microfinance on mortality and nutrition in children under five amongst the very poor in India: study protocol for a cluster randomized controlled trial.

BACKGROUND: The United Nations Millennium Development Goals include targets for the health of children under five years old. Poor health is linked to poverty and microfinance initiatives are economic interventions that may improve health by breaking the cycle of poverty. However, there is a lack of reliable evidence to support this. In addition, microfinance schemes may have adverse effects on health, for example due to increased indebtedness. Rojiroti UK and the Centre for Promoting Sustainable Livelihood run an innovative microfinance scheme that provides microcredit via women's self-help groups (SHGs). This pilot study, conducted in rural Bihar (India), will establish whether it is feasible to collect anthropometric and mortality data on children under five years old and to conduct a limited cluster randomized trial of the Rojiroti intervention. METHODS/DESIGN: We have designed a cluster randomized trial in which participating tolas (small communities within villages) will be randomized to either receive early (SHGs and microfinance at baseline) or late intervention (SHGs and microfinance after 18 months). Using predesigned questionnaires, demographic, and mortality data for the last year and information about participating mothers and their children will be collected and the weight, height, and mid upper arm circumference (MUAC) of children will be measured at baseline and at 18 months. The late intervention group will establish SHGs and microfinance support at this point and data collection will be repeated at 36 months.The primary outcome measure will be the mean weight for height z-score of children under five years old in the early and late intervention tolas at 18 months. Secondary outcome measures will be the mortality rate, mean weight for age, height for age, prevalence of underweight, stunting, and wasting among children under five years of age. DISCUSSION: Despite economic progress, marked inequalities in child health persist in India and Bihar is one of the worst affected states. There is a need to evaluate programs that may alleviate poverty and improve health. This study will help to inform the design of a definitive trial to determine if the Rojiroti scheme can improve the nutrition and survival of children under five years of age in deprived rural communities. TRIAL REGISTRATION: Clinicaltrials.gov (study ID: NCT01845545). Registered on 24 April 2013.

C-reactive protein promotes platelet adhesion to endothelial cells: a potential pathway in atherothrombosis.

C-reactive protein (CRP) is a strong predictor for acute cardiovascular events. Several endothelial prothrombotic effects of CRP have been recently reported. This study examined the effect of CRP on bovine aortic endothelial cell (EC) activation and capacity to recruit human platelets under flow conditions using the cone and plate(let) analyser method. Human recombinant CRP promoted platelet adhesion in a dose- and time-dependent manner, with a maximal effect at 20 microg/ml (increase of 174% over baseline, P < 0.01). Similar effects were observed following incubation of EC with sera of transgenic mice that express human CRP (10 microg/ml). Anti-intercellular adhesion molecule-1 neutralising monoclonal antibody and nitric oxide donor, sodium nitroprusside, blocked the effect of CRP, reducing adhesion from 202% to 128% (P < 0.05) and 114% (P = 0.02) respectively. The pro-adhesive effect of CRP was abolished by calphostin C (a protein kinase C inhibitor), whereas the extracellular signal-regulated kinase antagonist, PD98059, did not have any effect. CRP promoted P-selectin expression on the EC surface and blockade of P-selectin reversed CRP-induced platelet adhesion. In conclusion, CRP promoted platelet adhesion to EC. Our results emphasise the possible role of CRP in linking inflammation and thrombosis and provide a potential mechanism for the high incidence of vascular events associated with high CRP levels.