SPADA

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 prevalence of disease

• 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