False-Positive Acanthamoeba Keratitis From Multiplex Polymerase Chain Reaction Diagnostics, a Case Series

The purpose of this study was to describe a series of cases in which multiplex polymerase chain reaction (PCR) suggested false-positive Acanthamoeba keratitis (AK).

Four patients without traditional risk factors for AK were referred after multiplex PCR (HealthTrackRx, Denton, TX) returned positive for Acanthamoeba. Clinical history, slitlamp examination, confocal microscopy, microbiologic cultures, viral PCR, and metagenomic deep sequencing (MDS) were reviewed. Clinical course and response to therapy were assessed.

Three patients had corneal involvement, and 1 had anterior scleritis without any corneal pathology. In all cases, corneal cultures were negative for Acanthamoeba. For the case with no corneal involvement, conjunctival culture was negative for Acanthamoeba. For all 4 cases, MDS was negative for Acanthamoeba. Two patients received a brief course of antiamoebic therapy, which was subsequently discontinued. The other 2 never received antiamoebic treatment. All patients recovered fully with therapy directed toward different underlying conditions. Final diagnoses included staphylococcal marginal keratitis, recurrent herpes simplex virus keratitis, undifferentiated anterior scleritis, and a chronic neurotrophic epithelial defect within a penetrating keratoplasty.

These cases illustrate the potential for false-positive multiplex PCR results for Acanthamoeba in patients without classic risk factors or expected clinical findings. Molecular diagnostic results should be interpreted alongside clinical assessment and adjunctive testing. Treating the patient rather than a single-test result remains essential in managing suspected AK.