False-positive B. pertussis NAAT may be the result of a lack of specificity of the test method, as discussed previously, or errors in the preanalytic or analytic phases of testing.
Environmental contamination may lead to false-positive results with amplification methods. All amplification assays are at high risk for contamination issues. Precautions must be taken to ensure proper specimen collection and segregation of "clean" and "dirty" areas (this applies to both the specimen collection area and the laboratory testing area).
A recent study has shown that aerosolized vaccines for B. pertussis may also cause false-positive test results. Some, but not all, B. pertussis vaccines contain genomic DNA in addition to bacterial antigens, and this DNA is susceptible to amplification in NAAT assays. Health care professionals that administer these vaccines should take strict precautions if they are also responsible for specimen collection from patients who are being tested for possible pertussis infection.
Suggestions for preventing false-positive results as described above include the following:
- Use of multiplex assays (an assay that measures more than one analyte at a time simultaneously in a single run) or a confirmatory testing algorithm to confirm all positive results.
- Segregation of "clean" and "dirty" areas for specimen collection and testing.
- Testing only patients that have clinical symptoms of pertussis.