Keratitis In Contact Lens Wearers Research Articles

Twenty‐five years of acanthamoeba diagnostics in Austria

AbstractAcanthamoeba spp. are ubiquitous free‐living amoebae and do not need a host. They can, however, cause disease upon accidental contact with a potential host. The most common Acanthamoeba infection in humans is the so‐called Acanthamoeba keratitis (AK), occurring mainly in contact lens wearers.The first case of AK was reported in the early seventies and in the mid‐eighties the association between AK and contact lens wear was discovered. Today, acanthamoebae are among the most important causative agents of keratitis in contact lens wearers. AK often shows a severe progression, which is due to a lack of awareness but also to the lack of specific treatment. The dormant cysts pose a particular problem, often residing within the tissue and leading to reinfection after termination of treatment. In industrialized countries the annual incidence of AK lies between 0.1–1 cases per 100 000 inhabitants, with a marked regional variation depending on contact lens wear habits and mode of water supply.Our institution is the Austrian reference laboratory for Acanthamoeba diagnostics. All samples from patients with suspected AK are screened for Acanthamoeba spp. by culture and PCR in parallel, and all detected amoebae are genotyped. We currently have an annual incidence of AK of around 0.2 cases per 100 000 inhabitants, with >90% of cases occurring in contact lens wearers. In contrast to other countries, we do not see any seasonality and in contrast to the early years, today, males and females are equally represented, the most affected group being the 21–30‐year‐olds. The vast majority of cases are unilateral and many cases have a prolonged progression, in some cases infections remain viable for >1 yr. The predominant genotype is Acanthamoeba T4, other common genotypes are T3, T5, T6, T10 and T11.

Clinical and molecular diagnosis of Acanthamoeba keratitis in contact lens wearers in southern Brazil reveals the presence of an endosymbiont.

Acanthamoeba keratitis (AK) is an infection that is mostly observed in contact lens wearers. It is often misdiagnosed causing delays in the administration of the correct treatment. The aim of this study was to report the outcome of clinical and molecular diagnosis of AK cases during the summer of 2019 in the southern region of Brazil. Three suspected cases of AK were discovered after an ophthalmic examination at a public hospital in the city of Porto Alegre. These cases were then confirmed through laboratory diagnosis (cell culture and molecular analysis by PCR and sequencing). In each of the three clinical sample cell cultures of corneal scraping and molecular analysis confirmed the presence of Acanthamoeba spp., all belonging to the morphological group II and to the genotype T4, which is the most common genotype associated with AK. In addition, Acanthamoeba spp. isolated from one of the clinical samples was found to harbor the Candidatus Paracaedibacter acanthamoeba, a bacterial endosymbiont. The presence of Ca. Paracaedibacter acanthamoeba in clinical isolates requires further research to reveal its possible role in the pathogenicity of Acanthamoeba infections.

Acanthamoeba keratitis in contact lens wearers in a tertiary center of Tunisia, North Africa

PurposeTo analyze the epidemiological and clinical features of Acanathamoeba keratitis AK and to assess the risk factors of this corneal infection in contact lens CL wearers in a tertiary center of Tunisia, North Africa. MethodsWe carried out a retrospective study between January 2008 and December 2019 in the ophthtalmology department of a referral center, Sousse, Tunisia. A review of the chart of 248 patients using CL and diagnosed with presumed infectious keratitis was done.Socio demographic, risk behaviors and microbiological findings in case of AK were analyzed. The mean follow-up was 18 months (1 month–4 years). ResultsAK was diagnosed in 29 cases (11.7% of contact lens wearers with infectious keratitis). These 29 cases were analyzed. The mean age at the time of diagnosis was 33, 44 ± 26, 9 years. Almost of the patients (13; 44.82%) used soft monthly disposable contact lenses. Some risk behaviors related to contact lens wearing were found in our study like not washing and drying hands before CL wear, sleeping in CL, topping off, not respecting the adequate replacement frequency and showering or swimming in CL.After treatment, visual acuity improved only in 10 cases (34.48%), remained the same in 11 cases (37.93%) and worsened in 8 cases (27.58%). ConclusionClinicians must suspect AK in each CL wearer with suggestive clinical signs to allow earlier treatment and better prognosis. Public prevention messages that encourage CL wearers to respect the hygiene rules should be broadly applicable to each person using any type of CL, to minimize the risk of AK.

Development of uracil-DNA-glycosylase-supplemented loop-mediated isothermal amplification coupled with nanogold probe (UDG-LAMP-AuNP) for specific detection of Pseudomonasaeruginosa.

Pseudomonas aeruginosa (P. aeruginosa) is an important opportunistic pathogen that causes serious infections in humans, including keratitis in contact lens wearers. Therefore, establishing a rapid, specific and sensitive method for the identification of P. aeruginosa is imperative. In the present study, the uracil-DNA-glycosylase-supplemented loop-mediated isothermal amplification combined with nanogold labeled hybridization probe (UDG-LAMP-AuNP) was developed for the detection of P. aeruginosa. UDG-LAMP was performed to prevent carry over contamination and the LAMP reactions can be readily observed using the nanogold probe. A set of 4 primers and a hybridization probe were designed based on the ecfX gene. The UDG-LAMP reactions were performed at 65°C for 60 min using the ratio of 40% deoxyuridine triphosphate to 60% deoxythymidine triphosphate. The detection of UDG-LAMP products using the nanogold labeled hybridization probe, which appeared as a red-purple color, was examined at 65°C for 5 min with 40 mM MgSO4. The UDG-LAMP-AuNP demonstrated specificity to all tested isolates of P. aeruginosa without cross reaction to other bacteria. The sensitivity for the detection of pure culture was 1.6×103 colony-forming units (CFU) ml−1 or equivalent to 3 CFU per reaction while that of polymerase chain reaction was 30 CFU per reaction. The detection limit of spiked contact lenses was 1.1×103 CFU ml−1 or equivalent to 2 CFU per reaction. In conclusion, the UDG-LAMP-AuNP assay was rapid, simple, specific and was effective for the identification of P. aeruginosa in contaminated samples.

Risk for microbial keratitis: Comparative metaanalysis of contact lens wearers and post-laser in situ keratomileusis patients

To compare the risk for microbial keratitis in contact lens wearers stratified by wear schedule with the risk after laser in situ keratomileusis (LASIK). Hamilton Eye Institute and Department of Ophthalmology, University of Tennessee Health Science Center, Memphis, Tennessee, USA. Comparative metaanalysis and literature review. An extensive literature search was performed in the PubMed database between December 2014 and July 2015. This was followed by a metaanalysis using a mixed-effects modeling approach. After 1year of daily soft contact lens wear, there were fewer microbialkeratitis cases than after LASIK, or approximately 2cases fewer cases per 10 000 (P=.0609). If LASIK were assumed to have essentially a 1-time risk for microbial keratitis, 5years of extrapolation would yield 11 more cases per 10 000 with daily soft contact lens wear than with LASIK, or approximately 3 times as many cases (P<.0001). The extended use of soft contact lenses led to 12 more cases at 1year than LASIK,or approximately 3 times as many cases (P<.0001), and 81 more cases at 5years (P<.0001). When incorporating an estimated 10% retreatment rate for LASIK, these results changed very little. Microbial keratitis is a relatively rare complication associated with contact lens use and LASIK postoperatively. The risk for microbial keratitis was similar between patients using contactlenses for 1year compared with LASIK. Over time, the risk for microbial keratitis was higher for contact lens use than for LASIK, specifically with extended-wear lenses.

Isolation and Genotyping of Acanthamoeba spp. as Neglected Parasites in North of Iran.

Acanthamoeba, a free-living amoeba, is widely distributed in the environment, water sources, soil, dust, and air. It can cause keratitis in contact lens wearers with poor hygiene and also fatal granulomatous amebic encephalitis (GAE) in immunocompromised hosts. The aim of this study was to gain some insights into the distribution and genotypes of the potentially pathogenic species of Acanthamoeba present in water sources in north of Iran. Total 43 Acanthamoeba species were isolated from 77 water samples taken from different water sources within the Mazandaran province in Northern Iran (Sari city and suburbs). Isolates were identified based on cyst and trophozoite morphological characteristics as well genetics. PCR fragments corresponding to the small-subunit 18S rRNA gene were sequenced for 20 of 43 positive isolates. The results revealed that 83.3% of sequenced isolates belonged to the T4 genotype and the rest belonged to the T2 genotype. Our results indicated that Acanthamoeba is widely distributed in Sari city. As the incidence in Iran of amoebic keratitis has increased in recent years, the exact estimation of the prevalence of this amoeba and its predominant genotype may play a crucial role in prevention of the disease. Sari city has several rivers, seashores, and natural recreational amenities, which attract visitors during the year. This is the first report of Acanthamoeba genotypes from water sources in Sari city, Mazandaran province of Iran, and the results suggest that more attention is needed to protect the visiting population and immunocompromised individuals.

Experimental infection of T4 Acanthamoeba genotype determines the pathogenic potential.

T4 is the Acanthamoeba genotype most related to cases of granulomatous amoebic encephalitis (GAE) in immunocompromised patients and of keratitis in contact lens wearers. The determination of the pathogenic potential of Acanthamoeba clinical and environmental isolates using experimental models is extremely important to elucidate the capacity of free-living organisms to establish and cause disease in hosts. The aim of this study was to compare and evaluate the histopathology and culture between two different routes of experimental infection of T4 Acanthamoeba isolated from environmental and clinical source in mice (intracranial and intraperitoneal). Swiss isogenic healthy mice were inoculated with 10(4) trophozoites by intracranial (IC) and intraperitoneal (IP) routes and observed during 21days. The brains from animals inoculated by the IC route were collected and from the animals of the IP inoculation group, the brains, livers, kidneys, spleens, and lungs were removed. The organs were prepared and appropriately divided to be evaluated with histopathology and culture. There was no significant difference between the inoculation routes in terms of isolates recovery (χ(2) = 0.09; p = 0.76). In the IC group, isolate recovery rate was significantly higher in histopathology than the one achieved by culture (χ(2) = 6.45; p < 0.01). Experimental infection revealed that all isolates inoculated could be considered invasive because it was possible to recover evolutive forms of Acanthamoeba in both routes. This work represents the first in vivo pathogenicity assay of primary isolation source in Central region of Brazil showing in vivo pathogenicity and hematogenous spread capacity of these protozoa, improving the knowledge on free-living amoebae isolates.

Acanthamoeba T4, T5 and T11 isolated from mineral water bottles in southern Brazil.

Acanthamoeba is a protist potential pathogen, capable of causing a blinding keratitis in contact lens wearers and disseminated infection, leading to granulomatous amebic encephalitis in immunocompromised individuals. This amoeba is a ubiquitous organism that has been isolated from various domestic water systems, such as cooling towers and hospital water networks. The objective of this work was to investigate the presence of Acanthamoeba in mineral water bottles marketed in Porto Alegre, southern Brazil. Positive samples were further classified at the genotype level after sequencing the ASA.S1 region of 18S rDNA gene. Six of the eight isolates belonged to T5 genotype, one to T4 genotype, and one was T11. Several genotypes have been reported worldwide as causative of pathologies in humans, including genotypes T4, T5 and T11. Overall, the widespread distribution of potentially pathogenic Acanthamoeba strains in the studied source demands more awareness within the public and health professionals, because this pathogen is emerging as a risk for human health worldwide.

Characterization of a New Pathogenic Acanthamoeba Species, A. byersi n. sp., Isolated from a Human with Fatal Amoebic Encephalitis

Acanthamoeba spp. are free‐living amoebae that are ubiquitous in natural environments. They can cause cutaneous, nasopharyngeal, and disseminated infection, leading to granulomatous amebic encephalitis (GAE) in immunocompromised individuals. In addition, they can cause amoebic keratitis in contact lens wearers. Acanthamoeba GAE is almost always fatal because of difficulty and delay in diagnosis and lack of optimal antimicrobial therapy. Here, we report the description of an unusual strain isolated from skin and brain of a GAE patient. The amoebae displayed large trophozoites and star‐shaped cysts, characteristics for acanthamoebas belonging to morphology Group 1. However, its unique morphology and growth characteristics differentiated this new strain from other Group 1 species. DNA sequence analysis, secondary structure prediction, and phylogenetic analysis of the 18S rRNA gene confirmed that this new strain belonged to Group 1, but that it was distinct from the other sequence types within that group. Thus, we hereby propose the establishment of a new species, Acanthamoeba byersi n. sp. as well as a new sequence type, T18, for this new strain. To our knowledge, this is the first report of a Group 1 Acanthamoeba that is indisputably pathogenic in humans.

Resistance and growth of Fusarium spp. in contact lens disinfectant solutions

Purpose: Fusarium spp. can cause fungal keratitis in contact lens wearers and an outbreak of infection was associated with use of a multipurpose disinfectant solution (MPS). Here, the efficacy of contact lens care solutions against Fusarium strains was investigated.

Contact Lens Cases: The Missing Link in Contact Lens Safety?

To summarize a variety of issues associated with contact lens case contamination and discuss appropriate methods that can limit this. A literature review was undertaken investigating the major factors associated with case contamination, with specific reference to the major pathogens associated with contamination, the role of bacterial biofilms, and methods that can limit contamination. The use of antimicrobial cases, regular case cleaning and case replacement, avoidance of topping up solutions, and not using tap water to rinse cases all appear to be important in avoidance of significant case contamination. Contact lens case contamination is a significant public health concern and may contribute significantly to the development of microbial keratitis in contact lens wearers. Patients should be reminded that they must clean and disinfect their lens cases daily, should avoid the use of tap water for rinsing them, must not top up their solutions, must take into careful consideration where and how the cases are stored during the time that lenses are being worn and that they must be replaced regularly. The adoption of these methods will substantially reduce the levels of contamination of cases with pathogenic microbes.

Contact Lens-Associated Fusarium Keratitis in Switzerland

Fusarium has been an exceptionally rare cause of infectious keratitis. A recent outbreak of Fusarium keratitis in contact lens wearers in North America and Asia has been associated with the multipurpose disinfection solution ReNu with MoistureLoc (Bausch&Lomb). We report a series of Fusarium keratitis in Swiss contact lens wearers. A multicentre retrospective case review of patients with corneal ulceration and a positive microbiological identification of Fusarium species was undertaken. Between September 2005 and August 2007, six cases of Fusarium keratitis were identified. Patients were 39 to 63 years of age. All patients were using disposable soft contact lenses for at least two years. Four patients used daily wear disposable lenses. Two patients were wearing 1-monthly disposable lenses and used ReNu with MoistureLoc solution. Due to multiresistant Fusarium, enucleation was required in two cases and an emergency keratoplasty was performed in three cases. An optical keratoplasty was undertaken in one case that developed corneal scarring. Final visual acuity in patients with preserved eyes ranged from light perception to 8 / 20. Exposure to ReNu with MoistureLoc is not the only risk factor for Fusarium keratitis. In addition to antifungal therapy, an early keratoplasty with excision of the infected tissue seems mandatory to improve prognosis.

Clinical Features and Outcomes of Fusarium Keratitis Associated With Contact Lens Wear

To describe the clinical features and outcomes among contact lens wearers with Fusarium keratitis. A retrospective observational review of all cases of culture-proven Fusarium keratitis among contact lens wearers from three hospitals in Hong Kong Island were included. The clinical features, hygiene habits, and clinical outcomes were reviewed. Sixteen patients (17 eyes) were diagnosed with Fusarium keratitis associated with contact lens wear. One patient had bilateral involvement. Six patients had a central lesion; four had paraxial lesions; one had paraxial and peripheral lesions; and the rest had peripheral lesions. Ten (62.5%) patients reported using ReNu multipurpose cleaning solution. Most patients had poor contact lens hygiene habits. One patient required systemic antifungal treatment. No surgical intervention was required in any of the patients. The clinical features of Fusarium keratitis in contact lens wearers can be variable. Although fungal infection is reported rarely, clinicians should maintain a high index of suspicion for it when examining patients with contact lens-associated microbial keratitis. Education on proper contact lens care should be reinforced. Early and appropriate treatment may lead to satisfactory visual outcomes.

Microbial Keratitis and the Role of Rub and Rinsing

Recent outbreaks of microbial keratitis in contact lens wearers have involved various pathogens, including Acanthamoeba and Fusarium species. Specific reasons for the marked increase in microbial keratitis, particularly those involving species typically rarely involved in contact lens infection, remain unknown. Possible contributing factors include inadequacies of various multipurpose solutions against certain pathogens; inadequate lens care hygiene, including elimination of the digital rubbing step; poor contact lens storage case hygiene; and the introduction of new soft contact lens materials that may promote adherence of certain pathogens, particularly when a digital rubbing step is eliminated. Although there is some conflict of opinion in the literature regarding the necessity for a mechanical rub during lens cleaning and disinfection, growing evidence supports the reestablishment of a digital rub component to multipurpose solution lens care systems. This article reviews the literature on whether such a process should be recommended to contact lens wearers.

Molecular characterization, biofilm analysis and experimental biofouling study of Fusarium isolates from recent cases of fungal keratitis in New York State.

BackgroundTo characterize Fusarium isolates from recent cases of fungal keratitis in contact lens wearers, and to investigate fungal association with MoistureLoc solution.MethodsWe studied six fungal isolates from recent cases of keratitis in New York State. The isolates were characterized by nucleotide sequencing and phylogenetic analyses of multiple genes, and then typed using minisatellite and microsatellite probes. Experimental fungal biofilm formation was tested by standard methods. MoistureLoc solutions were tested in biofouling studies for their efficacy in elimination of Fusarium contamination.ResultsFusarium solani – corneal ulcers (2 isolates), lens case (1 isolate), and F. oxysporum – corneal ulcer (1 isolate), eye (1 isolate), were recovered from five patients. An opened bottle of MoistureLoc solution provided by a patient also yielded F. solani. Two distinct genotypes of F. solani as well as of F. oxysporum were present in the isolated strains. Remarkably, F. solani strains from the lens case and lens solution in one instance were similar, based on phylogenetic analyses and molecular typing. The solution isolate of F. solani formed biofilm on contact lenses in control conditions, but not when co-incubated with MoistureLoc solution. Both freshly opened and 3-month old MoistureLoc solutions effectively killed F. solani and F. oxysporum, when fungal contamination was simulated under recommended lens treatment regimen (4-hr). However, simulation of inappropriate use (15 – 60 min) led to the recovery of less than 1% of original inoculum of F. solani or F. oxysporum.ConclusionTemporary survival of F. solani and F. oxysporum in MoistureLoc suggested that improper lens cleaning regimen could be a possible contributing factor in recent infections.

Report on Testing From an Investigation of Fusarium Keratitis in Contact Lens Wearers

Recent reports of disproportionate outbreaks of microbial keratitis caused by Fusarium solani have led to the removal of the Bausch & Lomb multipurpose lens care solution ReNu With MoistureLoc ("MoistureLoc") from the global market. Previous studies have shown an increased risk of contact lens-related corneal infection in connection with overnight wear, noncompliant lens wearing and lens care behaviors, specific treatment regimens, and other patient-related and non-patient-related factors. The purpose of the laboratory evaluations reported in this article were to observe the effects of levels of simulated lens care noncompliance on the antimicrobial efficacy of multipurpose solutions following recent reports of F. solani keratitis. Two multipurpose contact lens care solutions, MoistureLoc and ReNu MultiPlus multipurpose solution ("ReNu MultiPlus"), were tested under conditions that attempted to simulate the possible effect of the noncompliant behaviors reported to Bausch & Lomb as part of the investigation into cases of Fusarium keratitis. Testing conditions included simulated multiple reuse of solutions and evaporation of solutions. The biocidal efficacy of MoistureLoc and other tested solutions was reduced under conditions that simulated the possible impact of solution reuse. Further investigation of MoistureLoc and ReNu MultiPlus suggests that although efficacy with ReNu MultiPlus was maintained across a variety of noncompliant conditions, the MoistureLoc formula could be rendered less effective under certain conditions. Under conditions simulating the possible impact of noncompliance, the MoistureLoc solution showed reduced biocidal efficacy. In contrast, ReNu MultiPlus retained a higher level of biocidal activity under the same conditions.

Mycobacterium chelonae Keratitis

To describe the microbiologic diagnosis of putative Mycobacterium chelonae keratitis in a soft contact lens wearer by initial evaluation of Gram- and Kinyoun (acid fast)-stained smears of fluid from patient's contact lens care system. Corneal ulcer of suspected Acanthamoeba etiology developed in a 28-year-old soft contact lens wearer. After corneal scrapings were negative, microbiologic consultation led to evaluation of stained smears and culture of fluid from patient's contact lens care system. Gram stain of smears showed a polymicrobic flora distinguished by numerous gram-positive, beaded, tightly banded, "diphtheroid-like" bacilli strongly suggestive of a rapidly growing mycobacterial species. Kinyoun-stained smears revealed innumerable acid-fast bacilli singly and in tightly woven bundles (cords), which culturally proved to be M. chelonae. Treatment with ciprofloxacin and amikacin resolved the ulcer. Diagnosis of M. chelonae keratitis in contact lens wearers is often delayed or even overlooked. Additionally, in the absence of overt corneal injury, eg, trauma or surgery, a source for the infecting mycobacterial species in the setting of contact lens wear has not been identified. If searched for, however, as in the present case, the patient's contact lens care system may serve as the reservoir for the microorganism. Staining for acid-fast bacilli is further recommended when smears of contact lens care solution of a patient with a corneal ulcer shows the presence of gram-positive "diphtheroid-like" organisms.

Ulcerative keratitis in contact lens wearers.

To determine the clinical microbiological characteristics of corneal ulcers in contact lens wearers. A retrospective study of 23 patients admitted to our department with contact lens-related corneal ulcers during a 43-month period. Detailed demographic data, the type of contact lens, duration of lens wear, and wearing schedule were derived from a self-administered questionnaire. The severity of the ulcer; cultures of corneal scrapings, storage solutions, and contact lenses; treatment; and final outcome were evaluated. Of the 86 cases of ulcerative keratitis admitted during the study period, 23 (26.74%) were attributed to contact lens use. Most patients were young women from urban areas. All of them were using soft contact lenses for 3 days to 20 years. Five patients used daily-wear lenses as extended-wear lenses. Most ulcers (47.82%) were mild; 30.43% were moderate; and 21.47% were severe. Corneal scrapings for cultures were obtained in 15 of the cases and were positive in 10 (43.47%) of them, whereas in 33.33% of the culture-positive storage solutions and in 66.67% of the culture-positive contact lenses, corneal scrapings were negative. Pseudomonas aeruginosa was the most frequent isolated pathogen (60%). The final visual acuity was 20/40 or better in 60.87% of the cases. Contact lens use is an important risk factor for the development of ulcerative keratitis, with P. aeruginosa remaining the predominant pathogen. It seems important to culture contact lenses and contact lens storage solutions, in addition to the corneal scrapings, and the role of initial therapy for the corneal ulcers remains important.

Cytotoxic activities of alkylphosphocholines against clinical isolates of Acanthamoeba spp.

Free-living amoebae of the genus Acanthamoeba are causing serious chronic conditions such as destructive keratitis in contact lens wearers or granulomatous amoebic encephalitis in individuals with compromised immune systems. Both are characterized by the lack of availability of sufficiently effective and uncomplicated, manageable treatments. Hexadecylphosphocholine (miltefosine) is licensed for use as a topical antineoplastic agent, but it is also active in vitro against several protozoan parasites, and it was applied very successfully for the treatment of human visceral leishmaniasis. The aim of our study was to evaluate the efficacy of hexadecylphosphocholine and other alkylphosphocholines (APCs) against Acanthamoeba spp. The in vitro activities of eight different APCs against three Acanthamoeba strains of various pathogenicities were determined. All substances showed at least amoebostatic effects, and some of them disrupted the amoebae, as shown by the release of cytoplasmic enzyme activity. Hexadecylphosphocholine exhibited the highest degree of cytotoxicity against trophozoites, resulting in complete cell death at a concentration as low as 40 microM, and also displayed significant cysticidal activity. Hexadecylphosphocholine may be a promising new candidate for the topical treatment of Acanthamoeba keratitis and, conceivably, even for the oral treatment of granulomatous amoebic encephalitis.

Microbial keratitis in Hong Kong: relationship to climate, environment and contact-lens disinfection

Microbial keratitis has been studied in Hong Kong as a representative sub-tropical climate of south China. An 18-month investigation in 1997/98 of 223 cases of ulcerative keratitis (presumed microbial) was conducted in the 2 million population of Shatin and Kowloon at the Prince of Wales and Hong Kong Eye Hospitals respectively with comprehensive microbiology. A case-control study was pursued at the same time between 45 contact-lens wearers (CLW) developing microbial keratitis and 135 lens-wearing volunteers matched for age, sex, educational status and visual acuity. Home water supplies were sampled for Acanthamoeba. Previous ocular surface disease and trauma (preventable by wearing goggles for grinding) were common predisposing causes while cosmetic wear of contact lenses was responsible for 26% of cases overall. Pseudomonas aeruginosa was the commonest bacterium isolated, from both CLW and non-CLW, with infection being acquired within the community. These 28 pseudomonads remained fully sensitive to the third-generation cephalosporins, aminoglycosides and quinolone antibiotics, which is very encouraging. Fungi were isolated, predominantly Fusarium sp., but less commonly than expected. A fungal/bacterial ratio was obtained of 1 17 , while in comparison, the expected ratio for a tropical climate ranges from 1 5 (Singapore) to 1 2 (South India). Acanthamoeba was the second commonest microbe isolated from keratitis of CLW. The domestic water environment of 8% of homes of both patients and controls wearing contact lenses was colonized with Acanthamoeba. Lack of hygiene, use of tap water for storing lenses, failure to airdry lens-storage cases or use of one-step hydrogen peroxide disinfectant were identified as risk factors for keratitis in CLW. The study results commend use of multipurpose solutions by CLW in Hong Kong to achieve the lowest expected rates of infection.