The correct answer is C, confirm results using other techniques such as direct fluorescent antibody assay (DFA) or modified Kinyoun's acid-fast stain.  False-positive results have recently been reported in some commercial EIA kits.  Routine confirmatory testing can be beneficial in detecting problems with diagnostic assays and is essential when confronting a possible outbreak situation.  Laboratory results can have important implications for patients, as well as use of personnel and other resources.