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E. Y. Tu, C. E. Joslin, M. E. Shoff, L. M. Nijm; Polymicrobial Acanthamoeba Keratitis. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5936.
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Early signs of Acanthamoeba Keratitis (AK) are highly nonspecific and may mimic viral dendritic keratitis as well as suppurative bacterial or fungal keratitis. While many of these pathogens have been anecdotally detected in AK cases with supportive microbiologic evidence, other cases suspected of coinfection may, consequently, simply be misclassified. The source, incidence and consequence of coinfection remain, therefore, unknown, knowledge of which may reduce diagnostic delay and enhance understanding of the pathogenesis of AK. We report the occurrence of polymicrobial infections in a large cohort of patients with AK.
Retrospective review of 111 AK patients diagnosed at the University of Illinois Eye and Ear Infirmary between June, 2003 and November, 2008 for an additional diagnosis of infectious keratitis. Method of AK diagnosis has been previously described. Positive culture results at any time were used to determine the presence of non-AKkeratitis.
Previous treatment with topical antibiotics or antivirals was common, and only 7 patients had an additional microbiologic diagnosis of infectious keratitis, all bacterial, at any point during their care. Cultured organisms included methicillin sensitive S. aureus, S. viridans group, and P. aeruginosa. Of these, three patients developed a concomitant Infectious Crystalline Keratopathy (ICK) during their treatment for AK. Gemella hemolysans and Delftia acidovorans were also isolated well after AK-curative penetrating keratoplasty. Visual outcomes in this group varied widely, but were generally poorer. 5 additional cases cultured coagulase negative Staphylococci, a presumed contaminant.
At our center, the number of patients with documented coinfection at any time was low, but those patients generally fared more poorly. In vitro studies indicate an increase in pathogenicity when cocultured. The low culture rate may be a function of the efficacy of modern anti-infectives, widely available for empiric therapy of recalcitrant keratitis and the low community culture rate prior to referral. This may either mask the role of associated pathogens or potentially reduce their impact. Regardless, considering the rarity of each entity, the association of AK and bacterial keratitis, especially ICK, is significant, despite current antibiotic use. Therefore, the possibility that other pathogenic organisms may significantly alter the clinical course in AK should be considered, requiring a higher index of clinical suspicion and promoting a different therapeutic approach.
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