A false positive diagnosis for an infectious disease should be considered if:
(1) the infection is diagnosed at an unusual time of the year
(2) the patient does not have typical features of the infection
(3) the patient has been vaccinated for the condition
(4) the molecular test is weakly positive
(5) other indications of an infection (positive serology, positive culture) are negative
(6) the rate of positives in a laboratory is very high
A true epidemic may feature most or all of these factors. Their occurrence should prompt a review of the results for a reality check.
Sources of nucleic acid that can result in false positive test:
(1) vaccines that contain organism nucleic acids
(2) environmental contamination (surfaces, clothing, etc)
(3) poor specimen collection and handling practices
