August 30, 2016 SPADA Meeting Book

Pre-event/Post-event

• Test > 90% sensitivity • Pre-event prevalence of smallpox is zero: – If test has 95% specificity, 10 tests done per month, in 6 to 8 sites, every month there will be 3 or 4 false positives • Post-event prevalence of smallpox is finite: – If test has 95% specificity, 1000 tests done per week, every week 50 results will be false positives – If test has 99% sensitivity, 1000 tests done per week, 10 results will be false negatives

Test Parameters

• Sensitivity and specificity are independent of the l f di preva ence o sease • Predictive value positive and negative vary with disease prevalence (Bayes’ Theorem) • Implications for smallpox testing “pre-event” and “post-event”: use of tests for decision making