False positives of screening in large-scale population with low infection rate of an infectious diseasea： a modeling analysis / 上海预防医学

ObjectiveTo explore the positive predictive value （PPV） and false positive （FP） number of screening test in mass testing when the prevalence of infection is low. MethodsAssuming a population of 20 million with the prevalence of disease infection ranging from 0.1% to 5.0%， PPV， true positive （TP） and FP numbers were calculated under different scenarios of combination of sensitivity （99.0%， 99.5%， and 100.0%） with specificity （97.0%， 97.5%， 98.0%， 98.5%， 99.0%， 99.5%， and 99.9%）. ResultsFor low infection prevalence （≤5.0%）， specificity has a greater impact on PPV than sensitivity； with the decrease of infection prevalence， the increase in PPV elevates when the specificity increases. When the infection prevalence is >1.0%， the closer the specificity is to 99.9%， the closer the PPV is to 100.0%. However， when the infection prevalence is <1.0%， the maximum PPV is only about 90.0%. When the infection rate is 0.1%， a screening test with more than 99.0% sensitivity could detect about 20 thousand TP cases in a population of 20 million. Additionally， the FP and PPV are estimated to be 599 thousand and 3.2% if the specificity is 97.0%， and 20 thousand and 50.0% if the specificity is 99.9%. When the infection rate is 1.0%， a screening test with ≥99.0% sensitivity and ≥97.0% specificity could detect about 0.198‒0.200 million TP cases； and the number of FP decreases from 594 thousand to 20 thousand when the specificity increases from 97.0% to 99.9%. When the infection rate is 5.0%， a screening test with ≥99.0% sensitivity and ≥97.0% specificity could detect about 0.99‒1.00 million TP cases； and the number of FP decreases from 570 thousand to 19 thousand when the specificity increases from 97.0% to 99.9%. When the infection prevalence is ≤5.0% in a total population of 20 million， there are about 20，000 FP cases even if the sensitivity and specificity reach the maximum values of 100.0% and 99.9%， respectively. ConclusionWhen the population is large and the infection prevalence is low， in addition to improving the specificity of the screening test in mass testing， the problem of a large number of false positives cannot be ignored.

Problems and tentative solutions in the control of gonorrhea in the community

Hospitality girls reporting at the Balibago Social Hygiene Clinic, Angeles City between November 1978 and February 1979 for their regular VD check-up were studied. Similarly, hospitality girls seen at the Social Hygiene Clinics at Makati, Pasay City, and Para$aque, Metro Manila were studied from July to November 1978 to compare the prevalence rate of gonococcal infection