Correlation between surface water contamination with amoeba and the onset of symptoms and diagnosis of amoeba-like keratitis

Infectious keratitis: A review

Globally, infectious keratitis is the fifth leading cause of blindness. The main predisposing factors include contact lens wear, ocular injury and ocular surface disease. Staphylococcus species, Pseudomonas aeruginosa, Fusarium species, Candida species and Acanthamoeba species are the most common causal organisms. Culture of corneal scrapes is the preferred initial test to identify the culprit organism. Polymerase chain reaction (PCR) tests and in vivo confocal microscopy can complement the diagnosis. Empiric therapy is typically commenced with fluoroquinolones, or fortified antibiotics for bacterial keratitis; topical natamycin for fungal keratitis; and polyhexamethylene biguanide or chlorhexidine for acanthamoeba keratitis. Herpes simplex keratitis is mainly diagnosed clinically; however, PCR can also be used to confirm the initial diagnosis and in atypical cases. Antivirals and topical corticosteroids are indicated depending on the corneal layer infected. Vision impairment, blindness and even loss of the eye can occur with a delay in diagnosis and inappropriate antimicrobial therapy.

Isolation and identification of free-living amoeba from the hot springs and beaches of the Caspian Sea

Free-living amoeba (FLA) such as Acanthamoeba, Naegleria, Balamuthia, and Vermamoeba have been identified from both natural and human-made environments such as Hot springs and spa. Naegleria fowleri causes Primary Amoebic Meningoencephalitis (PAM), while Acanthamoeba and Balamuthia cause chronic granulomatous encephalitis. Acanthamoeba also can cause cutaneous lesions and Amoebic Keratitis (AK) that is associated with contact lens use or corneal trauma. FLA are known to serve as host of and vehicles for diverse intracellular organisms. This study aimed was to identify the presence of FLA in the hot springs and beaches of the Caspian Sea in Ramsar tourist town located in the northern part of Iran. Water samples were collected in sterile bottles and were transferred to the laboratory. One litre of each sample passed through the nitrocellulose membrane filter. Each filter insert was then placed in non-nutrient agar plates already seeded with lawn culture of Escherichia coli. Positive samples were analyzed by morphological keys and Polymerase chain reaction (PCR) using 18S rDNA gene and ITS region to identify amoeba isolates. A total of 81 water sampled were tasted. After identified using the morphological key and PCR assay, 54 (66.6%) of the samples were positive for FLA. Ten of the samples were identified as Acanthamoeba (belong to T3, T4, and T5 genotypes), three as Vermamoeba vermiformis, four as Naegleria (3 N.australiensis and 1 N.grubery). Only one sample was positive Vahlkampfia. The presence of thermotolerant FLA in the Hot springs and beaches of the Caspian Sea as places for recreational purposes or wellness may be a potential health risk.

Prevalence and seasonal variation of Acanthamoeba in domestic tap water in greater Sydney, Australia

BACKGROUND

This study examined the prevalence of free-living Acanthamoeba in domestic tap water in the greater Sydney region, Australia, and determined any seasonal variation in prevalence.

METHODS

Fifty-four participants were included in this study following approval from an institutional human research ethics committee. Each participant self-collected two samples (one in summer and another in winter) from the surface of the drain of the bathroom sink using an instructional kit. The samples were cultured by inoculating onto a non-nutrient agar plate seeded with Escherichia coli and incubation at 32°C for two weeks. The plates were microscopically examined for the presence of free-living amoeba. DNA was isolated from 20 samples and a polymerase chain reaction (PCR) assay was performed for amplification of the partial sequence of the 18S ribosomal RNA gene. The PCR amplified products were sequenced using Sanger sequencing and genotyping was performed based on the variation in nucleotide sequences.

RESULTS

A total of 97 samples were collected over the two collection periods, with 28.6 per cent of samples morphologically classified as Acanthamoeba. The summer period yielded 16 of 54 (29.6 per cent) samples classified as Acanthamoeba, while the winter period yielded 12 of 43 (27.9 per cent) samples classified as Acanthamoeba. There was no statistically significant difference (p = 0.85) between the prevalence of free-living Acanthamoeba in summer compared to winter. Phylogenetic analysis showed that 15 of 20 (75 per cent) isolates belonged to genotype T4, the most frequent genotype isolated in Acanthamoeba keratitis.

CONCLUSION

The prevalence of free-living Acanthamoeba characterised morphologically in domestic tap water of the greater Sydney region was higher than expected, especially considering the low incidence of Acanthamoeba keratitis in Australia. However, this study did not find variation between seasons. As the T4 genotype was most common, Sydney-based practitioners must always consider Acanthamoeba as a possible causative organism in cases of microbial keratitis, regardless of the season.

The relationship between environmental sources and the susceptibility of Acanthamoeba keratitis in the United Kingdom

PURPOSE

To determine whether Acanthamoeba keratitis (AK) patients have higher rates of Acanthamoeba and free-living amoeba (FLA) colonising domestic sinks than control contact lens (CL) wearers, and whether these isolates are genetically similar to the corneal isolates from their CL associated AK.

METHODS

129 AK patients from Moorefield Eye Hospital, London and 64 control CL wearers from the Institute of Optometry were included in this study. The participants self-collected home kitchen and bathroom samples from tap-spouts, overflows and drains using an instructional kit. The samples were cultured by inoculating onto a non-nutrient agar plate seeded with Escherichia coli, incubated at 32°C and examined for amoebae by microscopy for up to 2 weeks. Partial sequences of mitochondrial cytochrome oxidase genes (coxA) of Acanthamoeba isolates from four AK patients were compared to Acanthamoeba isolated from the patient's home. The association between sampling sites was analysed with the chi-square test.

RESULTS

A total of 513 samples from AK patients and 189 from CL controls were collected. The yield of FLA was significantly greater in patients' bathrooms (72.1%) than CL controls' bathrooms (53.4%) (p<0.05). Spouts (kitchen 6.7%, bathroom 11%) had the lowest rate of Acanthamoeba isolation compared to drains (kitchen 18.2%, bathroom 27.9%) and overflow (kitchen 39.1%, bathroom 25.9%) either in kitchens or bathrooms (p<0.05). There was no statistically significant difference between the average prevalence of Acanthamoeba in all three sample sites in kitchens (16.9%) compared to all three sample sites in bathrooms (21.5%) and no association for Acanthamoeba prevalence between AK patients and CL controls. All four corneal isolates had the same coxA sequence as at least one domestic water isolate from the patients' sink of the kitchen and the bathroom.

CONCLUSION

The prevalence of Acanthamoeba and FLA was high in UK homes. FLA colonisation was higher in AK patients compared to controls but the prevalence of Acanthamoeba between AK patients and CL controls domestic sinks was similar. This study confirms that domestic water isolates are probably the source of AK infection. Advice about avoiding water contact when using CL's should be mandatory.

The rising incidence of Acanthamoeba keratitis: A 7-year nationwide survey and clinical assessment of risk factors and functional outcomes

Purpose

To evaluate the incidence of Acanthamoeba keratitis in the Netherlands between 2009 and 2015 and to analyse predicting factors for treatment outcome.

Methods

Patient characteristics, diagnostic methods, diagnostic delay, therapy prior to and after diagnosis, and visual outcome were obtained from medical files of all patients diagnosed with Acanthamoeba keratitis in the Netherlands between 2009 and 2015. A logistic regression analysis on treatment failure, defined as a best corrected visual acuity of less than 20/40 Snellen decimals (i.e. >0.3 logMAR or an approximate loss of three lines of visual acuity) and/or the need for keratoplasty, was performed to determine predicting factors.

Results

Two hundred and twenty-four eyes of 224 patients were included. Ninety-five percent of the patients were contact lens wearers, of whom 74% wore soft contact lenses. The number of cases increased from 16 in 2009 to 49 in 2015. This resulted in an estimated incidence of 1 in 21,000 for soft contact lens wearers in 2015. Eighty-seven eyes (39%) met the criteria for treatment failure. In a multivariable regression analysis, higher age at presentation, a higher severity stage and corticosteroid use before diagnosis were positively correlated with treatment failure. Early referral to a cornea specialist was associated with better clinical outcomes.

Conclusions

Although Acanthamoeba keratitis is still a relatively uncommon disease, the incidence in soft contact lens wearers has increased to reach 1 in 21,000 in 2015. Treatment failure occurred in 39% of cases, with age, higher severity stage, corticosteroid use before diagnosis and indirect referral to a cornea specialist as important risks factors.

Water Exposure and the Risk of Contact Lens-Related Disease

PURPOSE

To describe the association of water exposure with contact lens (CL)-related disease and explore the guidelines regarding water exposure to CL wearers, provided by CL manufacturing industry, global public health, and CL-related professional associations.

METHODS

A review of the literature was conducted by searching PubMed, MEDLINE, and Web of Science databases up to September 2017 for articles published or translated in English using keywords: contact lens* AND tap water OR swimming OR showering OR water exposure AND microbial keratitis OR Acanthamoeba keratitis OR corneal infiltrate* OR ocular adverse event*. References in all relevant publications were also reviewed.

RESULTS

Water exposure during CL wear is associated with complications ranging from sterile corneal infiltrative events to sight-threatening infections. Despite the documented risks due to water exposure, water-related habits are common among CL wearers. This suggests a lack of awareness and understanding regarding the risks among CL wearers and potentially CL practitioners. Discrepancies exist in guidelines for CL hygiene and compliance provided by the CL manufacturing industry, global public health, and CL-related professional associations. There is also widespread use of water imagery within CL marketing and packaging materials. These factors may give rise to confusion among wearers and may contribute toward risk-taking behaviors.

CONCLUSIONS

Consensus among stakeholders about water and CL care is needed. Guidelines should unequivocally advocate for the avoidance of any water exposure including handling CLs with wet hands, rinsing CLs or storage cases in tap water, showering while wearing CLs and swimming with CLs without wearing goggles.

Association Between Season, Temperature and Causative Organism in Microbial Keratitis in the UK

PURPOSE

Microbial keratitis (MK) is a major cause of corneal blindness worldwide. Variations in season and temperature can affect MK incidence due to specific causative organisms; however, few studies have examined these factors in the UK.

METHODS

Retrospective review of all corneal scrapes from patients with MK presenting to Manchester Royal Eye Hospital, UK, between January 2004 and December 2015. Manchester's monthly temperature data were obtained from Met Office UK. Analysis was performed using logistic regression.

RESULTS

From 4229 corneal scrapes, 1539 organisms grew (90.6% bacteria, 7.1% fungi, and 2.3% Acanthamoebae sp.). Gram-positive bacteria grew with increasing temperature [odds ratio (OR) 1.62, 95% CI: 1.11-2.39, P = 0.014], and fungi grew with decreasing temperature (OR 0.29, 95% CI: 0.16-0.51, P < 0.001). Moraxella sp. grew with decreasing temperature (OR 0.91, 95% CI: 0.86-0.96, P = 0.001). Compared with winter, overall culture positivity was significantly less likely in summer (OR 0.57, 95% CI: 0.38-0.87, P = 0.008) and spring (OR 0.65, 95% CI: 0.43-0.99, P = 0.045). Gram-negative bacteria were more likely in summer (OR 1.48, 95% CI: 1.06-2.09, P = 0.022) and autumn (OR 1.75, 95% CI: 1.24-2.47, P = 0.001). Candida sp. were less likely in summer (OR 0.25, 95% CI: 0.07-0.82, P = 0.027) and autumn (OR 0.18, 95% CI: 0.05-0.62, P = 0.009), and Acanthamoeba sp. were less likely in summer (OR 0.39, 95% CI: 0.15-0.92, P = 0.037) and spring (OR 0.26, 95% CI: 0.08-0.69, P = 0.011).

CONCLUSIONS

Herein we report variation in the incidence of MK-causing organisms by season and temperature; this finding may aid clinicians in predicting possible causative organisms for MK at differing times of the year.

Non-contact lens related Acanthamoeba keratitis

The purpose of the study is to describe epidemiology, clinical features, diagnosis, and treatment of Acanthamoeba keratitis (AK) with special focus on the disease in nonusers of contact lenses (CLs). This study was a perspective based on authors' experience and review of published literature. AK accounts for 2% of microbiology-proven cases of keratitis. Trauma and exposure to contaminated water are the main predisposing factors for the disease. Association with CLs is seen only in small fraction of cases. Contrary to classical description experience in India suggests that out of proportion pain, ring infiltrate, and radial keratoneuritis are seen in less than a third of cases. Majority of cases present with diffuse infiltrate, mimicking herpes simplex or fungal keratitis. The diagnosis can be confirmed by microscopic examination of corneal scraping material and culture on nonnutrient agar with an overlay of Escherichia coli. Confocal microscopy can help diagnosis in patients with deep infiltrate; however, experience with technique and interpretation of images influences its true value. Primary treatment of the infection is biguanides with or without diamidines. Most patients respond to medical treatment. Corticosteroids play an important role in the management and can be used when indicated after due consideration to established protocols. Surgery is rarely needed in patients where definitive management is initiated within 3 weeks of onset of symptoms. Lamellar keratoplasty has been shown to have good outcome in cases needing surgery. Since the clinical features of AK in nonusers of CL are different, it will be important for ophthalmologists to be aware of the scenario wherein to suspect this infection. Medical treatment is successful if the disease is diagnosed early and management is initiated soon.

Acanthamoeba spp. in Contact Lenses from Healthy Individuals from Madrid, Spain

Purpose

Acanthamoeba keratitis (AK) is a painful and potentially blinding corneal infection caused by Acanthamoeba spp. In Madrid, environmental studies have demonstrated a high presence of these free-living amoebae in tap water. Since most of AK cases occur in contact lenses (CL) wearers with inadequate hygiene habits, the presence of Acanthamoeba in discarded CL has been studied and compared with other common etiological agents of keratitis, such as Pseudomonas aeruginosa and Staphylococcus aureus.

Methods

One hundred and seventy-seven healthy individuals from Madrid contributed their discarded CL and answered a questionnaire on hygiene habits. DNA was extracted from the CL solution and analyzed by real-time PCR for Acanthamoeba, Pseudomonas aeruginosa and Staphylococcus aureus. These CL and their solutions were also cultured on non-nutrient agar to isolate Acanthamoeba.

Results

Among the 177 samples, Acanthamoeba DNA was detected in 87 (49.2%), P. aeruginosa DNA in 14 (7.9%) and S. aureus DNA in 19 (10.7%). Cultivable amoebae, however, were observed in only one sample (0.6%). This isolate was genotyped as T4. The habits reported by this CL owner included some recognized risk factors for AK, but in this study only the practice of “not cleaning the CL case” presented some statistical significant association with Acanthamoeba DNA presence. Detection of the investigated bacterial DNA did not demonstrate statistical significant association with the studied practices, but the presence of P. aeruginosa revealed a possible inhibition of Acanthamoeba in these samples.

Conclusions

The PCR results suggest a high presence of Acanthamoeba spp. in healthy CL wearers from Madrid, but we can assume that CL solutions are properly disinfecting the CL since only 1.1% of the positive PCR samples correspond to viable amoebae and, after four years, only one participant reported stronger ocular problems. Nevertheless, more studies are necessary to corroborate this hypothesis.

[Acanthamoeba keratitis]

Early diagnosis and appropriate therapy are key elements for a good prognosis in Acanthamoeba keratitis (AK). AK should be considered in any case of corneal trauma complicated by exposure to soil or contaminated water, and in all contact lens (CL) wearers. A presumptive diagnosis of AK can be made clinically and with in vivo confocal microscopy, although a definitive diagnosis requires identification of Acanthamoeba on direct scraping, histology, or identification of Acanthamoeba DNA by polymerase chain reaction (PCR). We use cysticidal drugs for treating AK because encysted forms are more resistant than trophozoites to treatment. The treatment protocol used a biguanide (PHMB 0.02% or chlorhexidine 0.02%) and a diamidine (propamidine 0.1% or hexamidine 0.1%). New diagnostic modalities and more specific topical anti-amoebic treatments would substantially benefit patients with AK.

A year long study of the presence of free living amoeba in Spain

Free-living amoeba such as Acanthamoeba and Balamuthia mandrillaris can act as opportunistic parasites on a wide range of vertebrates and they are becoming a serious threat to human health due to the resistance of their cysts to harsh environmental conditions, disinfectants, some water treatment practices and their ubiquitous distribution. This work was carried out in order to study the presence of these free-living amoebae (FLA) and their possible seasonality in a continental-Mediterranean climate in different types of water. For this purpose, a total of 223 water samples were collected during one year from four drinking water treatment plants (DWTP), seven wastewater treatment plants (WWTP) and six locations of influence (LI) on four river basins from Spain. Water samples were concentrated using the IDEXX Filta-Max(®) system and analyzed by a triplex real time PCR that detects Acanthamoeba, B. mandrillaris and Naegleria fowleri. Agar plates were also seeded for Acanthamoeba culture. From the three FLA studied, N. fowleri was not detected in any sample while B. mandrillaris was found at the entrance of a DWTP; this being, to our knowledge, the first report of these protozoa in water worldwide. On the other hand, the presence of Acanthamoeba observed was higher, 94.6% of the studied points were positive by real time PCR and 85.2% by culture, resulting in 99.1% positive for Acanthamoeba with both methods. All genetically analyzed Acanthamoeba were genotype T4 but nine different T4/DF3 sequences were observed, three of them being described for the first time, assigning new codes. No seasonal distribution of Acanthamoeba was found. These facts should serve as a warning to contact lens wearers of the risk of a poor hygiene when handling their contact lenses. It should also serve as a signal to physicians to consider FLA as a possible causative agent of nervous system infections as well as Acanthamoeba keratitis due to their high environmental presence shown in this study.

Recent outbreaks of atypical contact lens-related keratitis: what have we learned?

PURPOSE

To examine the public health implications of 2 recent outbreaks of atypical contact lens-related infectious keratitis.

DESIGN

Perspective based on the literature and authors' experience.

RESULTS

The contact lens-related Fusarium and Acanthamoeba keratitis outbreaks were each detected by dramatic rises seen in tertiary care centers in Singapore and the United States, respectively. Case-control studies of both outbreaks were able to identify a strong association with the use of different contact lens disinfection solutions. Their respective recalls resulted in a steep decline of Fusarium keratitis, but not of Acanthamoeba keratitis. Early investigations into each solution association implicated components not directly related to their primary disinfectant, but the true pathogenesis remains unknown. However, the number of Acanthamoeba cases individually attributed to each of almost all available disinfection systems exceeds the previously understood total United States incidence, suggesting other risk factors. Current standards do not require demonstration of anti-acanthamoebal activity. Yet, despite the inclusion of Fusarium in mandatory testing for solutions, current premarket testing was not predictive of the outbreak.

CONCLUSIONS

The 2 recent outbreaks of atypical contact lens-related keratitis have reinforced the value of tertiary care eye care centers in detecting early rises in rare infections and the power of adaptable, well-designed epidemiologic investigations. Although Fusarium keratitis has declined significantly with the recall of Renu with MoistureLoc (Bausch & Lomb Inc.), the persistence of Acanthamoeba keratitis demands fundamental changes in contact lens hygiene practices, inclusion of Acanthamoeba as a test organism, and contact lens disinfectant test regimens for all contact lens-related pathogens that are verifiably reflective of end user contact lens wear complications.

Prevalence of Acanthamoeba spp. and other free-living amoebae in household water, Ohio, USA--1990-1992

Knowledge of the prevalence of free-living amoebae (FLA) in US household water can provide a focus for prevention of amoeba-associated illnesses. Household water samples from two Ohio counties, collected and examined for amoebae during 1990-1992, were used to describe the prevalence of Acanthamoeba and other FLA in a household setting. Amoebae were isolated and identified by morphologic features. A total of 2,454 samples from 467 households were examined. Amoebae were found in water samples of 371 (79%) households. Sites most likely to contain amoeba were shower heads (52%) and kitchen sprayers (50%). Species of Hartmannella, Acanthamoeba, or Vahlkampfia were most common. Detection was higher in biofilm swab samples than in water samples. Detection of FLA and Acanthamoeba, at 79% and 51%, respectively, exceed estimates that have been published in previous surveys of household sources. We believe FLA are commonplace inhabitants of household water in this sample as they are in the environment.

Acanthamoeba keratitis: diagnosis and treatment update 2009

PURPOSE

To describe the current management of Acanthamoeba keratitis (AK).

DESIGN

A perspective based on the literature and author experience.

RESULTS

Early diagnosis and appropriate therapy are key to a good prognosis. A provisional diagnosis of AK can be made using the clinical features and confocal microscopy, although a definitive diagnosis requires culture, histology, or identification of Acanthamoeba deoxyribonucleic acid by polymerase chain reaction. Routine use of tissue diagnosis is recommended, particularly for patients unresponsive to treatment for AK. Topical biguanides are the only effective therapy for the resistant encysted form of the organism in vitro, if not always in vivo. None of the other drugs that have been used meet the requirements of consistent cysticidal activity and may have no therapeutic role. The use of topical steroids is controversial, but probably beneficial, for the management of severe corneal inflammatory complications that have not responded to topical biguanides alone. The scleritis associated with AK is rarely associated with extracorneal invasion and usually responds to systemic anti-inflammatory treatment combined with topical biguanides. Therapeutic keratoplasty retains a role for therapy of some severe complications of AK but not for initial treatment. With modern management, 90% of patients can expect to retain visual acuity of 6/12 or better and fewer than 2% become blind, although treatment may take 6 months or more.

CONCLUSIONS

Better understanding of the pathogenesis of the extracorneal complications, the availability of polymerase chain reaction for tissue diagnosis, and effective licensed topical anti-amoebics would substantially benefit patients with AK.

Temporal and seasonal trends in Acanthamoeba keratitis

PURPOSE

The purpose of this study was to assess the incidence and risk factors of Acanthamoeba keratitis (AK) over an 8-year period in a Canadian tertiary care setting.

METHODS

We retrospectively reviewed the medical records of 41 patients (42 eyes), who were diagnosed as having AK between January 1999 and December 2006 in the cornea clinic at the Toronto Western Hospital. The incidence and risk factors of AK were evaluated.

RESULTS

The number of cases per year increased from between 0 and 4 in the first 5 years to 9, 14, and 8 in the last 3 years. The annual increasing trend was statistically significant (P = 0.04). The month of onset of disease symptoms showed a trend toward onset in summer and fall and was statistically significant for the difference between January and August (P = 0.0094). The season of onset of disease symptoms showed a trend toward summer onset, and the difference between winter and summer was statistically significant (P = 0.02). 92.9% of cases occurred in contact lens wearers, particularly in soft contact lens wearers (82.1%).

CONCLUSIONS

The incidence of AK in Canada may be increasing since 2004. There is a seasonal trend toward disease onset in the warmer months.

The relative value of confocal microscopy and superficial corneal scrapings in the diagnosis of Acanthamoeba keratitis

PURPOSE

To compare the relative diagnostic value of confocal microscopy and superficial corneal cultures in the diagnosis of Acanthamoeba keratitis by using clinical and microbiologic definitions of disease.

METHODS

Results of confocal microscopy, superficial corneal smear, and superficial corneal culture were analyzed for validity against 2 different microbiologic and a clinical composite standard for Acanthamoeba keratitis.

RESULTS

In patients with both clinical characteristics and objective evidence of Acanthamoeba keratitis, confocal microscopy exhibited a sensitivity of 90.6% (95% confidence interval [CI]: 79.3%-96.9%) and a specificity of 100% (95% CI: 95.0%-100%). In patients with either positive culture or smear evidence of Acanthamoeba keratitis, confocal microscopy showed a sensitivity of 90.9% (95% CI: 78.3%-97.5%) and specificity of 90.1% (95% CI: 81.5%-95.6%). In strictly culture-positive patients, confocal microscopy showed a sensitivity of 92.9% (95% CI: 76.5%-99.1%) and a specificity of 77.3% (95% CI: 67.7%-85.2%). Of the 53 patients with Acanthamoeba keratitis, confocal microscopy was positive in 48 patients, whereas corneal smears and cultures were positive in 30 of 41 and 23 of 42 patients, respectively. Sensitivity of Acanthamoeba culture was 52.8% (95% CI: 38.6%-66.7%) in patients with a clinical diagnosis of Acanthamoeba keratitis. Simultaneous testing of smear and superficial corneal scraping resulted in a sensitivity of 83.0% (95% CI: 70.2%-91.9%), independent of the results of confocal microscopy.

CONCLUSIONS

As confocal microscopy comes into wider clinical use, it remains in need of clinical and pathologic correlation. When performed and interpreted by an experienced operator, confocal microscopy is both sensitive and specific in the diagnosis of Acanthamoeba keratitis. Contemporaneous corneal scrapings are independently sensitive in the detection of Acanthamoeba keratitis, and a combination of both diagnostic modalities offers the highest likelihood of rapidly and accurately diagnosing Acanthamoeba keratitis in patients with atypical keratitis.

Factors affecting the epidemiology of Acanthamoeba keratitis

Despite being a relatively rare disease in comparison with other forms of infectious keratitis, Acanthamoeba keratitis is a potentially blinding disease. Wide variations in the incidence of Acanthamoeba keratitis have been reported in both developed and developing countries. At the same time that contact lens wear was found to be responsible for the spread of the disease in developed countries, Acanthamoeba keratitis was considered a rare disease in developing countries compared with fungal and bacterial keratitis. In recent decades, the risk of getting Acanthamoeba keratitis has increased because of the increased proportion of contact lens wearers. This article introduces the different factors affecting the epidemiology of Acanthamoeba keratitis worldwide, presents a chronological review of the literature, and shows the progressive spread of Acanthamoeba keratitis in the last two decades in different geographical areas of the world. A detailed comparison of the incidence of the disease as reported in different studies in different countries is made. The impact of contact lenses and other factors, such as hot weather, virulence of Acanthamoeba strains, water sanitation and quality, the occurrence of environmental disasters such as flooding, and the wide environmental presence of Acanthamoeba cysts on the incidence of the disease, are discussed. In addition, the ability of Acanthamoeba cysts to resist different harsh conditions is reviewed.

Epidemiological characteristics of a Chicago-area Acanthamoeba keratitis outbreak

PURPOSE

To characterize Acanthamoeba keratitis (AK) cases and analyze the geographical distribution within the Chicago-Gary-Kenosha metropolitan area, Chicago, Illinois, USA.

DESIGN

Retrospective, population-based cohort study.

METHODS

All AK cases diagnosed at the University of Illinois at Chicago Cornea Service from June 1, 2003, to November 30, 2005, were included in analysis. Patients with keratitis were defined as cases through confocal microscopy, histology, and/or positive cultures. Exploratory analyses were performed to evaluate whether AK cases were unequally distributed geographically. County population data were extracted from US Census 2000 data, and rates were age-standardized to Cook County. Poisson regression analysis was used to estimate the age-standardized rate ratio (RR) between AK cases and county of residence. Current cases (June 1, 2003 to November 30, 2005) were compared with historical cases (June 1, 2000 to November 30, 2002) to determine if the current rate of AK diagnosis differed from historical rates.

RESULTS

Forty AK cases were diagnosed between June 1, 2003 and November 30, 2005. The average (+/-SD) age of patients with AK was 28.0 +/- 15.0 years (range, 13 to 70 years), 52.5% were men, and 95.0% wore contact lenses. Estimated RR measures demonstrated increased rates for all counties relative to Cook, and were significant for both DuPage County (RR 3.59; 95% confidence interval [95% CI] 1.44, 8.39) and Will County (RR 3.66; 95% CI 1.18 to 9.56). Current AK diagnosis rates were significantly higher than historical rates (RR 6.67; 95% CI 3.05 to 17.52).

CONCLUSIONS

AK cases are increasing in frequency. The increased rates are unevenly distributed in the study area. Further research is warranted to better understand the increase and unusual geographical distribution.

Acanthamoeba keratitis in England and Wales: incidence, outcome, and risk factors

AIM

To determine the incidence, regional variation in frequency, outcome, and risk factors for acanthamoeba keratitis (AK) in England and Wales.

METHODS

AK cases presenting from 1 October 1997 to 30 September 1999 were identified by the British Ophthalmic Surveillance Unit active reporting system. Clinical and patient postal questionnaire data were analysed.

RESULTS

106 reported cases met study criteria. The annual incidence for the 2 years was 1.26 and 1.13 per million adults and, for contact lens (CL) wearers, 21.14 and 17.53 per million. There was marked regional variation in incidence (0 to 85.13 per million adult CL wearers), with CL wearers in the south having a ninefold increased risk of AK compared with those resident in the north (95% confidence limits: 2.2-38.9, p<0.0001), and a threefold increased risk with hard as opposed to soft domestic water (95% confidence limits: 1.73 to 6.58, p<0.001). Treatment and outcome data were similar to those previously reported. 93/106 (88%) patients were CL wearers. Among these, 46/77 (60%) were disinfecting irregularly, and 20/63 (32%) had been swimming in CLs. One step hydrogen peroxide and chlorine release soft CL (SCL) disinfection systems were significantly over-represented among the cases. Among SCL users, one or more previously established risk factors for AK were identified in 50/55 (91%) patients.

CONCLUSIONS

The incidence was considerably higher than most previous estimates, and was static. The geographical variation in incidence may be partly related to the increase in risk associated with hard water. The fact that water quality can have such an effect on the risk of AK suggests that many CL wearers must be letting tapwater come into contact with their lenses or storage cases. Improved education for CL wearers and practitioners about hygiene practice and the variable efficacy of contact lens systems could be expected to reduce the incidence of this disease.

Atypical presentation of Acanthamoeba keratitis

PURPOSE

To present two cases of minimal pain Acanthamoeba keratitis to alert clinicians to remember Acanthamoeba when evaluating atypical cases of keratitis.

METHODS

The histories of two cases were reviewed with attention to clinical presentation subjective complaints, treatment, and long-term outcome.

RESULTS

In case 1, a 24-year-old man presented with decreased vision and an irritated feeling in his eye. He did not wear contact lenses. His initial diagnosis was adenoviral conjunctivitis. One month later, he was diagnosed with atypical herpes simplex keratitis and started on acyclovir. Two weeks later, he was referred to the Cornea Service. Further history revealed the patient to be a professional triathlete who trained by swimming in a fresh water pond. He was found to have an unusually high pain tolerance. Biopsy revealed Acanthamoeba. He was admitted for intensive therapy with neomycin, propamidine isethionate, and polyhexamethylene biguanide. Two years after diagnosis, he has best-corrected visual acuity of 20/100. In case 2, a 28-year-old man with known herpes simplex keratitis presented with decreased vision. He was started on topical trifluridine. After 6 weeks without improvement, he was referred for corneal evaluation. His eye always remained comfortable. Corneal sensation was markedly decreased. Further history revealed that he swam in fresh water. Biopsy was positive for Acanthamoeba. After 1 year of therapy with polyhexamethylene biguanide and neomycin, visual acuity was 20/200, and the patient underwent a corneal transplant.

CONCLUSION

Acanthamoeba keratitis must be considered in the differential diagnosis of keratitis, even without the classic presentation of severe pain and predisposing corneal trauma, including contact lens wear.

Climate variability and change in the United States: potential impacts on water- and foodborne diseases caused by microbiologic agents

Exposure to waterborne and foodborne pathogens can occur via drinking water (associated with fecal contamination), seafood (due to natural microbial hazards, toxins, or wastewater disposal) or fresh produce (irrigated or processed with contaminated water). Weather influences the transport and dissemination of these microbial agents via rainfall and runoff and the survival and/or growth through such factors as temperature. Federal and state laws and regulatory programs protect much of the U.S. population from waterborne disease; however, if climate variability increases, current and future deficiencies in areas such as watershed protection, infrastructure, and storm drainage systems will probably increase the risk of contamination events. Knowledge about transport processes and the fate of microbial pollutants associated with rainfall and snowmelt is key to predicting risks from a change in weather variability. Although recent studies identified links between climate variability and occurrence of microbial agents in water, the relationships need further quantification in the context of other stresses. In the marine environment as well, there are few studies that adequately address the potential health effects of climate variability in combination with other stresses such as overfishing, introduced species, and rise in sea level. Advances in monitoring are necessary to enhance early-warning and prevention capabilities. Application of existing technologies, such as molecular fingerprinting to track contaminant sources or satellite remote sensing to detect coastal algal blooms, could be expanded. This assessment recommends incorporating a range of future scenarios of improvement plans for current deficiencies in the public health infrastructure to achieve more realistic risk assessments.

Climate variability and change in the United States: potential impacts on water- and foodborne diseases caused by microbiologic agents

Exposure to waterborne and foodborne pathogens can occur via drinking water (associated with fecal contamination), seafood (due to natural microbial hazards, toxins, or wastewater disposal) or fresh produce (irrigated or processed with contaminated water). Weather influences the transport and dissemination of these microbial agents via rainfall and runoff and the survival and/or growth through such factors as temperature. Federal and state laws and regulatory programs protect much of the U.S. population from waterborne disease; however, if climate variability increases, current and future deficiencies in areas such as watershed protection, infrastructure, and storm drainage systems will probably increase the risk of contamination events. Knowledge about transport processes and the fate of microbial pollutants associated with rainfall and snowmelt is key to predicting risks from a change in weather variability. Although recent studies identified links between climate variability and occurrence of microbial agents in water, the relationships need further quantification in the context of other stresses. In the marine environment as well, there are few studies that adequately address the potential health effects of climate variability in combination with other stresses such as overfishing, introduced species, and rise in sea level. Advances in monitoring are necessary to enhance early-warning and prevention capabilities. Application of existing technologies, such as molecular fingerprinting to track contaminant sources or satellite remote sensing to detect coastal algal blooms, could be expanded. This assessment recommends incorporating a range of future scenarios of improvement plans for current deficiencies in the public health infrastructure to achieve more realistic risk assessments.