1. STUDY DESIGN FOR DIAGNOSTIC STUDY FOR MELIOIDOSIS Dr Direk Limmathurotsakul, MD MSc PhD

2. Introduction: 3 phases of study design Laboratory phase - develop test - test with few cases and healthy controls - prove of concept Case-control phase - test with definite cases and definite controls - calculate Se & Sp Prospective phase - test with disease- suspected patients - calculate Se, Sp, PPV & NPV

3. Introduction: 3 phases of study design Laboratory phase - develop test - test with few cases and healthy controls - prove of concept Case-control phase - test with definite cases and definite controls - calculate Se & Sp Prospective phase - test with disease- suspected patients - calculate Se, Sp, PPV & NPV Look promising

4. Introduction: 3 phases of study design Laboratory phase - develop test - test with few cases and healthy controls - prove of concept Case-control phase - test with definite cases and definite controls - calculate Se & Sp Prospective phase - test with disease- suspected patients - calculate Se, Sp, PPV & NPV Look promisingLook good

5. Introduction: 3 phases of study design Laboratory phase - develop test - test with few cases and healthy controls - prove of concept Case-control phase - test with definite cases and definite controls - calculate Se & Sp Prospective phase - test with disease- suspected patients - calculate Se, Sp, PPV & NPV Look promisingLook goodLook rubbish (GS problem)

6. Good guideline

7. Recommendation 1: Access index test’s ability to predict patient-relevant outcomes instead of test accuracy Recommendation 2: Access the concordance of difference tests instead of test accuracy Recommendation 3: Qualify the interpretation of “naïve” estimates of the index test’s performance Recommendation 4: Imperfect gold standard model

8. Recommended design for melioidosis Define need For example, estimate Se, Sp, PPV and NPV in a prospective design (to represent the real clinical situation) Define study population (that we would like to infer the estimated accuracy to) Next: select reference standard

9. Recommended design for melioidosis If there are more than one population, at least 2 diagnostic tests (3 tests are preferred) Those 2 tests should be based on 2 different biological mechanism (e.g. one antigen detection [culture] and one antibody detection [IHA]) If there is only one population, at least 3 diagnostic tests (5 tests are preferred) Those 3 tests should be based on 3 different biological mechanism (e.g. one antigen detection [culture / PCR assays], one antibody detection [IHA/ELISA], one clinical detection [ultrasonogram/CT scan])

10. Recommended design for melioidosis Consider repeated sampling and convalescent specimens Day 4 and Day 7 specimens may have clinical implication for changing the diagnosis and treatment Day 14 and Day 28 specimens may have clinical implication for starting oral treatment regimen Consider long-term outcome for relapse/recurrent infection Four-fold rising is arbitrary and based on imperfect gold standard. This should be evaluated with better approach Adequate sample size is required (enough diseased patients for sensitivity estimation is important than the total number)

11. Recommended design for melioidosis Select sites Appoint study team Train staff Provide GCP Conduct QC and monitoring Collect data Perform analysis Report results using STARD checklist Disseminate results

12. END