The Relative Value of Confocal Microscopy and Superficial Corneal Scrapings in the Diagnosis of Acanthamoeba Keratitis

Tu, Elmer Y.; Joslin, Charlotte E.; Sugar, Joel; Booton, Gregory C.; Shoff, Megan E.; Fuerst, Paul A.

doi:10.1097/ico.0b013e31816f27bf

Cited by 111 publications

(99 citation statements)

References 34 publications

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“…An association with reflective round bodies has been found in up to 85% of cases clinically presenting as Acanthamoeba keratitis (Mathers et al, 1996;Parmar et al, 2006). Sensitivities of around 90 to 100% have been described using confocal microscopy compared with much lower sensitivities of 0 to 50% using culture (Mathers et al, 1996;Parmar et al, 2006;Kanavi et al, 2007;Tu et al, 2008;Vaddavalli et al, 2011). Supporting laboratory evidence is still required as it is not possible to state with certainty if the round structures are definitely Acanthamoeba cysts or trophozoites.…”

Section: Pcr Detectionmentioning

confidence: 99%

Acanthamoeba keratitis: improving the Scottish diagnostic service for the rapid molecular detection of Acanthamoeba species

Alexander

Coyne

Jones

et al. 2015

Journal of Medical Microbiology

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Acanthamoeba species are responsible for causing the potentially sight-threatening condition, Acanthamoeba keratitis, which is commonly associated with contact lens use. In this report, we highlight the challenges faced using conventional laboratory identification methods to identify this often under-reported pathogen, and discuss the reasons for introducing the first national service in Scotland for the rapid and sensitive molecular identification of Acanthamoeba species. By comparing culture and molecular testing data from a total of 63 patients (n580 samples) throughout Scotland presenting with ocular eye disease, we describe the improvement in detection rates where an additional four positive cases were identified using a molecular assay versus culture. The testing of a further ten patients by confocal imaging is also presented. This report emphasizes the importance of continuing to improve clinical laboratory services to ensure a prompt, correct diagnosis and better prognosis, in addition to raising awareness of this potentially debilitating opportunistic pathogen. INTRODUCTIONAcanthamoeba keratitis is an uncommon but sightthreatening disease of the cornea caused by free-living protozoan amoebae belonging to the genus Acanthamoeba (Lorenzo- Morales et al., 2013). This painful, often unilateral eye disease may eventually progress to blindness and is associated with contact lens use but can also be diagnosed in non-contact lens wearers. Acanthamoeba species can be found in a variety of different environments including recreational and drinking water, soil and air (Gianinazzi et al., 2009;Legarreta et al., 2013;Rivera et al., 1991). Trophozoites and highly robust cysts can persist for years and are often resistant to drug treatments.Global increases of Acanthamoeba keratitis occurred during the 1970s and 1980s with links to contact lens use in over 85% of cases, which is consistent with recent data from America and Canada (Stehr-Green et al., 1989;Fraser et al., 2012;Page & Mathers, 2013). In addition, noncommercial saline solutions have been implicated as potential risk factors (Newton et al., 1986). The UK experienced an increase in cases during the 1990s which coincided with increased use of soft contact lenses (Illingworth et al., 1995).There is a lack of recent robust data on the prevalence of Acanthamoeba keratitis in Scotland, but based on a study by Seal et al. (1999), the incidence was 149 per million soft contact lens wearers compared with much lower incidence rates of around 18 to 21 per million in the rest of the UK (Radford et al., 2002). Presently, there are approximately 3.7 million contact lens wearers in the UK (British Contact Lens Association, http://www.bcla.org.uk/).An early, accurate diagnosis is crucial for achieving a better prognosis. However, conventional techniques to detect Acanthamoeba species may lack sensitivity, which is likely to result in the true prevalence being underestimated. The challenges of an early diagnosis are compounded by the ability of Acanthamoeba to mimic non-...

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Section: Pcr Detectionmentioning

confidence: 99%

Acanthamoeba keratitis: improving the Scottish diagnostic service for the rapid molecular detection of Acanthamoeba species

Alexander

Coyne

Jones

et al. 2015

Journal of Medical Microbiology

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“…17 In addition, initiation of anti-acanthamoebal therapy could reduce the sensitivity of culture and smear, as topical therapy might clear superficial infection but not deeper infection. In other words, some repeat cultures were likely false negatives, leading to an underestimate of the median clearance time.…”

Section: Discussionmentioning

confidence: 99%

“…When this model was performed for the entire patient population (n ¼ 32 eyes), the estimated median clearance time decreased to 38.7 days (95% CI 27.9-53.5 days). When we accounted for the imperfect sensitivity of culture and smear techniques for acanthamoeba diagnosis (assuming 83% sensitivity based on a previous study), 17 the sensitivity of acanthamoeba culture and smear techniques was even lower (eg, sensitivity ¼ 60%), the estimated clearance time increased to 52.7 days (95% CI 38.2-72.7 days). Still lower sensitivities would result in even longer estimations of the duration of infection.…”

Section: Clearance Time Estimatesmentioning

confidence: 99%

Microbiological cure times in acanthamoeba keratitis

Oldenburg

Keenan

Cevallos

et al. 2011

Eye

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Aims The purpose of this study was to estimate the duration of treatment necessary for sequential acanthamoeba laboratory tests from corneal scrapings to become negative, and to assess predictors that affect this duration period. Methods We included all patients with at least one positive acanthamoeba culture or Giemsa stain at the F.I. Proctor Foundation Microbiology Laboratory from 1996 to 2009. A parametric survival analysis was performed among patients with repeat cultures to assess significant predictors for extended clearance time. Simulations were performed to estimate clearance time in the entire patient population, assuming imperfect sensitivity. Results Thirty-seven patients with laboratory evidence of acanthamoeba had testing at 69 time points. The median clearance time among eyes with repeat cultures was 42.5 days (interquartile range (IQR) 22.0-82.0 days; unadjusted parametric model). Initial visual acuity was the only predictor significantly associated with clearance time in univariate analyses (Po0.0001). Using initial visual acuity as a predictor for clearance time among the entire patient population, the estimated clearance time decreased to 38.7 days (95% confidence interval (CI) 27.9-53.5 days). When the imperfect sensitivity of the culture technique was also taken into account, the estimated clearance time was 44.1 days (95% CI 31.9-61.0 days). Conclusion The duration of infection with acanthamoeba keratitis undergoing treatment has not been well characterized. In this report we estimate a median clearance time of approximately 6 weeks, with an IQR of 22-82 days.

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“…It is possible to directly identify Acanthamoeba trophozoites within the cornea using confocal microscopy and in experienced hands this technique is sensitive and specific 29 . Trophozoites and cysts may be revealed by staining the smear with H&E or Giemsa, while cysts are also readily identified using PAS and fluorescent stains, such as calcofluor white and acridine orange 30 .…”

Section: Laboratory Diagnosismentioning

confidence: 99%

Free living amoebae and human disease

Bursle¹,

Robson²

2016

Microbiol. Aust.

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Pathogenic FLA are ubiquitous protozoans and despite frequent human contact remain a rare cause of often devastating infection with poor prognosis. Given changes in climate, human encroachment into the environment, increasing immunosuppression, and improving diagnostic capacity, it is likely we will see increased cases in the future. Early diagnosis is challenging but crucial to achieving a favourable outcome. It is best facilitated by improved awareness of FLA disease, appropriate clinical suspicion and early diagnostic testing.

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The Relative Value of Confocal Microscopy and Superficial Corneal Scrapings in the Diagnosis of Acanthamoeba Keratitis

Cited by 111 publications

References 34 publications

Acanthamoeba keratitis: improving the Scottish diagnostic service for the rapid molecular detection of Acanthamoeba species

Acanthamoeba keratitis: improving the Scottish diagnostic service for the rapid molecular detection of Acanthamoeba species

Microbiological cure times in acanthamoeba keratitis

Free living amoebae and human disease

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