Prevalence of Acanthamoeba and other naked amoebae in South Florida domestic water

The purpose was to identify the prevalence of naked amoebae in tap water in south Florida to ascertain the risk of amoebal infections of the cornea in contact lens wearers. Over the course of a 2-year period, water samples were collected from sites throughout Broward, Palm Beach, and Dade counties, Florida. The presence of amoebae in samples was based on an enrichment cultivation method appropriate for Acanthamoeba. Amoebae were identified using diagnostic features discernable by light microscopy. A total of 283 water samples were processed and amoebae were noted in 80 of these. Acanthamoeba were found on 8 occasions (2.8%). The genera Hartmannella and Vahlkampfia, rarely involved in keratitis cases, were found in 3.5% and 2.8% of samples, respectively. A total of 19 different naked amoebae were recorded and amoebae (regardless of genus) were present in 19.4% of all samples. Previous surveys in England and Korea have shown that acanthamoebae are found in 15 to 30% of tap water samples in the home and have been associated with corneal infection in contact lens wearers. The incidence of acanthamoebae infection in the USA (2.8%) has been found to be lower than that in the UK and it has been postulated that this is related to the lack of a storage water tank in the roof loft space. However, the level of treatment of municipal water is clearly not effective at killing amoebal cysts (or trophozoites) as evidenced by the high occurrence of amoebae (19.4%) in this study.

ESCRS study of prophylaxis of postoperative endophthalmitis after cataract surgery: Preliminary report of principal results from a European multicenter study

PURPOSE

To report results in the European Society of Cataract & Refractive Surgeons (ESCRS) multicenter study of the prophylaxis of endophthalmitis after cataract surgery.

SETTING

Twenty-four ophthalmology units and eye clinics in Austria, Belgium, Germany, Italy, Poland, Portugal, Spain, Turkey, and the United Kingdom, with an administrative office in Ireland, coordinating center in England, and data management and statistical unit in Scotland.

METHODS

This partially masked randomized placebo-controlled multinational clinical study to evaluate prospectively the prophylactic effect of intracameral cefuroxime injection and/or perioperative levofloxacin eyedrops on the incidence of endophthalmitis after phacoemulsification cataract surgery began in September 2003 and was terminated early in January 2006. The study used random allocation of patients in a 2 x 2 factorial design.

RESULTS

By the end of 2005, complete follow-up records had been received for 13 698 study patients. Such a clear beneficial effect from the use of intracameral cefuroxime had been observed that it was agreed it would be unethical to continue the study and to wait for the completion of all follow-up procedures before reporting this important result. If total reported cases of endophthalmitis are considered, the incidence rate observed in those treatment groups not receiving cefuroxime prophylaxis (23 cases in 6862 patients) was almost 5 times as high (odds ratio [OR], 4.59; 95% confidence interval [CI], 1.74-12.08; P = .002) as that in the groups receiving this treatment (5 cases in 6836 patients). If only cases proved to be due to infection are considered, the rate was more than 5 times as high (OR, 5.32; 95% CI, 1.55-18.26; P = .008) in the treatment groups not receiving cefuroxime. Although the use of perioperative levofloxacin eyedrops as prophylaxis was also associated with a reduction in the observed incidence rate of postoperative endophthalmitis, this effect was smaller and was not statistically significant, whether total reported cases or only cases proven to be due to infection are used in calculating the rates. As not all follow-up procedures are complete, it is possible that further cases of endophthalmitis may be reported; however, it is not expected that this will alter the main conclusion. Nevertheless, it is anticipated that successful completion of follow-up procedures in all patients will increase the total number in the study to approximately 16,000.

CONCLUSION

Intracameral cefuroxime administered at the time of surgery significantly reduced the risk for developing endophthalmitis after cataract surgery.

ESCRS study of prophylaxis of postoperative endophthalmitis after cataract surgery

PURPOSE

To present the development and design of the European Society of Cataract & Refractive Surgeons multicenter study of the prevention of postsurgical infective endophthalmitis after phacoemulsification and to describe the process for its successful implementation and conduct.

SETTING

Twenty-four ophthalmology units and eye clinics in Austria, Belgium, Germany, Italy, Poland, Portugal, Spain, Turkey, and the United Kingdom, with an administrative office in Ireland, coordinating center in England, and data management and statistical unit in Scotland.

METHODS

This partially masked randomized placebo-controlled multinational clinical study was designed to evaluate prospectively the prophylactic effect of intracameral cefuroxime and/or perioperative topical levofloxacin on postoperative endophthalmitis after cataract surgery. Random allocation was based on a 2 x 2 factorial design that included participating centers as a class variable. Real-time electronic data collection monitored study progress and provided weekly outcome tables, monthly recruitment summaries, and quarterly analytical reports for the study's Data Monitoring Committee, which evaluated the safety and efficacy by Internet-based conferences.

RESULTS

A 2-year lead time was required to meet harmonized standards of clinical research in the European Union, obtain ministerial authorization in 3 countries, gain institutional approvals at 24 hospitals, and procure indemnity insurance for surgical centers. Informed consent instruments, designed to comply with national health policies, were translated into 8 languages. The use of information technology to collect study data enabled the organizers to evaluate individual eligibility at enrollment, adherence with study medications during and after surgery, and postoperative status during follow-up.

CONCLUSION

This international cooperative study provided the opportunity to estimate the current incidence of endophthalmitis after cataract surgery in Europe and determine whether 1 or both of 2 antimicrobial regimens reduces the risk for postsurgical intraocular infection.

Molecular and physiological evaluation of subtropical environmental isolates of Acanthamoeba spp., causal agent of Acanthamoeba keratitis

Previous molecular examination of Acanthamoeba spp. has resulted in the determination of distinct genotypes in this genus (designated T1-T12, T14). Genotype T4 has been responsible for the majority of cases of Acanthamoeba keratitis. Here we examine the relative abundance of environmental T4 isolates on beaches and ask whether they have temperature and salinity tolerances that could enhance pathogenicity. Twenty-four Acanthamoeba strains were isolated from beach sand (n = 20), soil (n = 3), and tap water (n = 1) in south Florida. Phylogenetic analysis identified 19 of 24 isolates as T4, the Acanthamoeba keratitis-associated genotype. The remaining isolates were genotype T5 (4) and T11 (1). Nearly all beach isolates were genotype T4, whereas the tap water and soil isolates were mostly T5. All amoebae grew at 0, 1.0, and 2.0% salt and 19 of 20 beach isolates also grew at 3.2%. No soil or tap-water acanthamoebae reproduced at 3.2%. All isolates grew at 37 degrees C and two (T5) at 42 degrees C. Little correlation existed between beach location, salt-tolerance, and genetic relatedness. Overall, the large majority of environmental isolates obtained were genotype T4, suggesting it may be the most common genotype in this environment and could be a potential source of Acanthamoeba keratitis infections.

Acanthamoeba keratitis update—incidence, molecular epidemiology and new drugs for treatment

A reliable figure for the expected incidence of Acanthamoeba keratitis of one per 30000 contact lens wearers per year has now been obtained from a combination of three cohort and three Questionnaire Reporting Surveys; 88% of cases wore hydrogel lenses and 12% wore rigid lenses. This figure now provides a basis for the expected number of cases against which to judge either epidemic outbreaks or effects of prevention with disinfecting solutions, better hygiene, or the use of disposable lenses. Molecular biology of Acanthamoeba has advanced considerably in the last 10 years with new automated sequencing technology. This has allowed the construction of a genotype identification scheme with 13 different genotypes against which to compare clinical isolates for epidemiological investigations or pathogenicity markers. So far, only four genotypes have been associated with keratitis of which the majority have been T4 but T3, T6, and T11 have each caused individual cases. Each genotype is heterogenous and can be further subdivided by comparison of sequences of diagnostic fragments of 18S rDNA, riboprinting by PCR-RFLP of 18S rDNA, or by mitochondrial DNA RFLP. Drug therapy has been revolutionised with the introduction of the biguanides-chlorhexidine or polyhexamethylene biguanide-with most but not all infections quickly resolving. Failure can still occur occasionally and further research is needed on more effective combination chemotherapy. A number of guanidines have been identified in this paper that could be usefully pursued as part of combination chemotherapy along with the alkylphosphocholines.

Determination of amoebicidal activities of multipurpose contact lens solutions by using a most probable number enumeration technique

Six multipurpose contact lens solutions [All-in-One, All-in-One (Light), ReNu MultiPlus, Optifree Express, Complete, and Solo-care soft] were tested for their efficacies against Acanthamoeba castellanii trophozoites and cysts by using a most probable number (MPN) technique for amoebic enumeration. Against trophozoites, All-in-One, ReNu Multiplus, and Optifree Express achieved total kill (log reduction of >3) after the manufacturer's minimum recommended disinfection time (MMRDT), with the remaining solutions failing to reach a log reduction of 1. After 24 h of exposure, all solutions proved trophozoiticidal, achieving, with the exception of Complete (log reduction of 3.13), total kill. Against cysts, All-in-One gave a log reduction of >3 within the MMRDT, with all other solutions failing to achieve a log reduction of 1. After 24 h of exposure, All-in-One achieved total kill of cysts (log reduction of 3.74), ReNu MultiPlus gave a log reduction of 3.15, and the remaining solutions reached log reductions of between 1.09 and 2.27. The MPN technique provides a simple, reliable, and reproducible method of amoebic enumeration that depends on simply establishing the presence or absence of growth on culture plates inoculated with a series of dilutions and determining the MPN of amoebae present from statistical tables. By use of this technique, two of the multipurpose solutions tested, ReNu MultiPlus and Optifree Express, demonstrated effective trophozoiticidal activities within the recommended disinfection times; however, only All-in-One proved effective against both trophozoites and cysts over the same time period. This MPN technique, which uses axenically produced trophozoites and mature, double-walled cysts, has the potential to form the basis of a national standard for amoebicidal efficacy testing of multipurpose contact lens disinfecting solutions.

Enhanced attachment of acanthamoeba to extended-wear silicone hydrogel contact lenses: a new risk factor for infection?

PURPOSE

To establish if silicone hydrogel (S-H) contact lenses could be a risk factor for Acanthamoeba infection by facilitating the attachment of trophozoites to their surface and transfer to the cornea and to determine the effect Acanthamoeba culture technique, patient wear, and Pseudomonas biofilm coating have on attachment to the S-H lens.

DESIGN

Experimental material study.

PARTICIPANTS AND CONTROLS

Attachment to a S-H lens was compared with that of a conventional hydrogel control lens. Sixteen replicates were carried out for both lens types under each test condition.

METHODS

Unworn S-H (PureVision; Bausch & Lomb, Kingston-Upon-Thames UK) and conventional hydrogel (Acuvue; Vistakon, Johnson & Johnson, Jacksonville, FL USA) lens quarters were incubated for 90 minutes in suspensions of liquid or plate-cultured Acanthamoeba castellanii trophozoites. Unworn, worn, and Pseudomonas biofilm coated S-H and hydrogel quarters were incubated for 90 minutes with plate-cultured trophozoites.

MAIN OUTCOME MEASURES

Trophozoites attached to one surface of each lens quarter were counted by direct light microscopy. Logarithmic transformation of data allowed the use of a parametric analysis of variance.

RESULTS

Lens polymer had a significant effect on attachment (P < 0.001), with higher numbers of trophozoites attaching to the S-H lens. Culture technique also had a significant effect on attachment (P = 0.013), with higher numbers of liquid-cultured organisms attaching to both lens types. A significant increase in attachment was demonstrated with worn and Pseudomonas biofilm-coated hydrogel lenses (P < 0.001); however, this difference was not seen with the S-H lens.

CONCLUSIONS

Acanthamoebal attachment to the S-H lenses was significantly greater than to the conventional hydrogel. Liquid-cultured trophozoites demonstrated a higher affinity for the lenses tested. Wear and bacterial biofilm coating had no effect on attachment to S-H lenses. The increased attachment found with the S-H lens may be an inherent characteristic of the polymer or a side effect of the surface treatment procedure to which the lenses are exposed. It is possible that S-H lenses are at greater risk of promoting Acanthamoeba infection if exposed to the organism because of the enhanced attachment characteristic of this new material.

Surface treatment or material characteristic: the reason for the high level of Acanthamoeba attachment to silicone hydrogel contact lenses

PURPOSE

To determine the reason for the high level of attachment of Acanthamebic to silicone hydrogel (SH) contact lenses. The effect surface treatment has on attachment is determined using silicone elastomer (SE) lenses.

METHODS

All test lenses were unworn. SH (PureVision), conventional hydrogel (Acuvue), treated SE (Silsoft), and untreated SE (Silsoft) lens quarters were incubated for 90 min with plate-cultured Acanthamoeba castellanii trophozoites. After incubation and rinsing, the trophozoites attached to one surface of each quarter were counted by direct light microscopy. Sixteen replicates were performed for each lens type. Logarithmic transformation of data allowed the use of parametric analysis of variance.

RESULTS

Lens polymer had a significant effect on attachment (P<0.001), with higher numbers of trophozoites attaching to the SH and SE (treated and untreated) lenses as compared with the conventional hydrogel. No significant difference in attachment was detected between the SH and SE (treated and untreated) lenses.

CONCLUSION

Acanthamoeba attachment to the SH lens was significantly greater than to the conventional hydrogel. The similarity in attachment to surface-treated and non-surface-treated SE lenses suggests that the increased attachment found with the SH lens may be an inherent characteristic of the polymer rather than an effect of the surface treatment procedure. It is possible that SH lenses are at greater risk of promoting Acanthamoeba infection if exposed to the organism because of the enhanced attachment characteristic of this new material.

18S ribosomal DNA typing and tracking of Acanthamoeba species isolates from corneal scrape specimens, contact lenses, lens cases, and home water supplies of Acanthamoeba keratitis patients in Hong Kong

We examined partial 18S ribosomal DNA (Rns) sequences of Acanthamoeba isolates cultured in a study of microbial keratitis in Hong Kong. Sequence differences were sufficient to distinguish closely related strains and were used to examine links between strains obtained from corneal scrape specimens, contact lenses, lens cases, lens case solutions, and home water-supply faucets of patients with Acanthamoeba. We also looked for evidence of mixed infections. Identification of Acanthamoeba Rns genotypes was based on sequences of approximately 113 bp within the genus-specific amplicon ASA.S1. This permitted genotype identification by using nonaxenic cultures. Of 13 specimens obtained from corneal scrapes, contact lenses, lens cases, or lens case solutions, 12 were Rns genotype T4 and the remaining one was Rns genotype T3. The sequences of corneal scrape specimens of two patients also were the same as those obtained from their contact lenses or lens case specimens. A possible triple-strain infection was indicated by three different T4 sequences in cultures from one patient's lenses. Although faucet water used by patients to clean their lenses is a possible source of infections, specimens isolated from the faucets at two Acanthamoeba keratitis patients' homes differed from their corneal scrape or lens specimens. The overall results demonstrate the potential of this Rns region for tracking Acanthamoeba keratitis strains in infections and for distinguishing single-strain and closely related multiple-strain infections even when other microorganisms might be present with the cultured specimens. They also confirm the predominance of Rns genotype T4 strains in Acanthamoeba keratitis infections.

Use of subgenic 18S ribosomal DNA PCR and sequencing for genus and genotype identification of acanthamoebae from humans with keratitis and from sewage sludge

This study identified subgenic PCR amplimers from 18S rDNA that were (i) highly specific for the genus Acanthamoeba, (ii) obtainable from all known genotypes, and (iii) useful for identification of individual genotypes. A 423- to 551-bp Acanthamoeba-specific amplimer ASA.S1 obtained with primers JDP1 and JDP2 was the most reliable for purposes i and ii. A variable region within this amplimer also identified genotype clusters, but purpose iii was best achieved with sequencing of the genotype-specific amplimer GTSA.B1. Because this amplimer could be obtained from any eukaryote, axenic Acanthamoeba cultures were required for its study. GTSA.B1, produced with primers CRN5 and 1137, extended between reference bp 1 and 1475. Genotypic identification relied on three segments: bp 178 to 355, 705 to 926, and 1175 to 1379. ASA.S1 was obtained from single amoeba, from cultures of all known 18S rDNA genotypes, and from corneal scrapings of Scottish patients with suspected Acanthamoeba keratitis (AK). The AK PCR findings were consistent with culture results for 11 of 15 culture-positive specimens and detected Acanthamoeba in one of nine culture-negative specimens. ASA.S1 sequences were examined for 6 of the 11 culture-positive isolates and were most closely associated with genotypic cluster T3-T4-T11. A similar distance analysis using GTSA.B1 sequences identified nine South African AK-associated isolates as genotype T4 and three isolates from sewage sludge as genotype T5. Our results demonstrate the usefulness of 18S ribosomal DNA PCR amplimers ASA.S1 and GTSA.B1 for Acanthamoeba-specific detection and reliable genotyping, respectively, and provide further evidence that T4 is the predominant genotype in AK.

Necrotizing fasciitis

Necrotizing fasciitis continues to occur due to beta-haemolytic streptococci but is now also recognized as being due to Vibrio spp. in fishermen and those in contact with warm water in the Gulf of Mexico and South-East Asia, including Hong Kong. Magnetic resonance image scanning has identified the extent of fasciitis and soft tissue oedema infiltrating fascial planes prior to necrosis presenting clinically and is a useful tool in early diagnosis. Surgical debridement or incisional drainage remains essential. An enhanced bactericidal response against beta-haemolytic streptococci has been found with a combination of penicillin and clindamycin. Intravenous immunoglobulin has been shown to reduce mortality if the necrotizing fasciitis is associated with the toxic shock syndrome, by decreasing the superantigen activity of the beta-haemolytic streptococci on cytokine release by T cells.

Salicylate inhibition of Acanthamoeba attachment to contact lenses: a model to reduce risk of infection

PURPOSE

Acanthamoeba attachment (adsorption) to hydrogel contact lenses is enhanced by Pseudomonas aeruginosa biofilm. The effect of sodium salicylate on Acanthamoeba attachment to biofilm-coated and uncoated hydrogel lenses was investigated.

DESIGN

Experimental study.

PARTICIPANTS AND CONTROLS

A minimum of 16 replicates were used for each test condition; a control condition using clean lenses without biofilm was included.

METHODS

Four groups of hydrogel contact lenses (etafilcon A) were pretreated with P. aeruginosa to form a biofilm. In addition, two more groups remained untreated. Quartered lenses of all six groups were then incubated in a suspension of A. castellanii trophozoites. Two batches of lenses had either 3 or 30 mM sodium salicylate added to the bacterial suspension (stage 1 intervention). Two other batches of lenses had salicylate added to the amoebal suspension (stage 2 intervention). One of the batches, which had a stage 1 intervention, had salicylate added at the second stage as well. The remaining batches received no salicylate exposure and included lenses with and without biofilm coating.

MAIN OUTCOME MEASURE

The outcome measure in this study was the number of Acanthamoeba trophozoites attached, per square centimeter, to the hydrogel surfaces.

RESULTS

Biofilm coating from P. aeruginosa gave a significantly increased attachment of A. castellanii trophozoites to the contact lens. When introduced at a first (biofilm) stage, second (trophozoite attachment) stage, or with intervention at both stages, 30 mM sodium salicylate reduced amoebal attachment to the hydrogel lens. When applied to both stages and when applied at stage 2 to the biofilm coated contact lenses, 3 mM sodium salicylate reduced amoebal attachment. The 3 mM concentration was not effective for the lower level of amoebae attachment to uncoated (nonbiofilm) lenses.

CONCLUSIONS

Sodium salicylate successfully reduced amoebal trophozoite attachment to hydrogel lenses. This was the result of one of the following possibilities or a combination thereof: inhibition of biofilm formation; a direct effect on the amoebae; an alteration in the biofilm-amoebal attachment and resulting modification of the hydrogel lens surface. The results of this study suggest the major action is at stage 2 (on amoebal attachment to lenses) and favors alteration of the biofilm-amoebal attachment mechanism. This study demonstrates salicylate's potential benefit as a component of contact lens care solutions, designed to reduce microbial attachment and the risk of infection.

Fluorescent oligonucleotide probes for clinical and environmental detection of Acanthamoeba and the T4 18S rRNA gene sequence type

The first genus- and subgenus-specific fluorescent oligonucleotide probes for in situ staining of Acanthamoeba are described. Sequences of these phylogeny-based probes complement the 18S rRNA and the gene encoding it (18S rDNA). The genus-specific probe (GSP) is a fluorescein-labeled 22-mer specific for Acanthamoeba as shown here by its hybridization to growing trophozoites of all 12 known Acanthamoeba 18S rDNA sequence types and by its failure to hybridize with amoebae of two other genera (Hartmannella vermiformis and Balamuthia mandrillaris), two human cell lines, and two bacteria (Pseudomonas aeruginosa and Escherichia coli). The sequence type T4-specific probe (ST4P) is a rhodamine-labeled 30-mer specific for Acanthamoeba 18S rDNA sequence type T4, as shown here in hybridization tests with trophozoites of all 12 sequence types. T4 is the subgenus group associated most closely with Acanthamoeba keratitis (AK). GSP also was tested with corneal scrapings from 17 patients with a high index of clinical suspicion of AK plus 5 patient controls. GSP stained both trophozoites and cysts, although nonspecific cyst wall autofluorescence also was observed. Results could be obtained with GSP in 1 to 2 days, and based on results from cell culture tests, the probe correctly detected the presence or absence of Acanthamoeba in 21 of 24 specimens from the 22 patients. The use of GSP with cultured trophozoites and cysts from corneal scrapings has illustrated the suitability of using fluorescent oligonucleotide probes for identification of the genus Acanthamoeba in both environmental and clinical samples. In addition, the use of ST4P with cultured amoebae has indicated the potential of oligonucleotide probes for use in subgenus classification.

Disinfection of contact lenses without tap water rinsing: is it effective?

PURPOSE

To establish the efficacy of the two most popular contact lens disinfecting systems--one-step hydrogen peroxide and multipurpose disinfecting solution--for 1 month's use in practice in the absence of tap water rinsing.

METHODS

This was a descriptive, prospective microbiological study of contact lens contamination with ideal hygiene compliance and new lenses and storage cases. One hundred and fifty contact lens wearers were instructed to avoid risk factors identified for Acanthamoeba infection. They were randomly assigned to use one of three disinfecting systems and taught to follow manufacturers' instructions. In addition, they were taught to avoid all use of tap water for contact lens hygiene, except for hand washing.

RESULTS

There was no isolation of Acanthamoeba from any lens storage case, precluding the chance of amoebic infection. The multi-purpose solution gave the lowest rate of bacterial contamination, with 78% sterility and 15% of cases with < 10(4) bacteria/ml. For both one-step peroxide and multi-purpose solutions, Gram-negative bacteria were reduced in frequency compared with values expected historically, while Bacillus sp. were found more frequently. Storage cases of both one-step peroxide systems leaked fluid.

CONCLUSIONS

On the basis of contamination in previous studies, when hydrogen peroxide and other chemical disinfectants were used together with tap water washing, it was expected that approximately 40% of lens storage cases would yield bacteria, often with a high count, and that up to 8% would yield Acanthamoeba. Such contamination did not occur, however, in this study. The multipurpose solution, for 1 month's use, gave the lowest rate of bacterial contamination with only 7% of storage cases harbouring bacteria at > 10(4)/ml and with 78% sterility. One of the two one-step hydrogen peroxide systems performed equally well. Importantly, Acanthamoeba was not isolated from any of the 150 storage cases. Whether lens storage cases need to be sterile or contain < 10(3) bacteria/ml solution within them is debatable, but it is essential that Acanthamoeba be absent from them.

Lack of evidence for systemic toxicity following topical chloramphenicol use

There has been considerable controversy regarding the safety of topical chloramphenicol in ophthalmic practice. The evidence for associated haematopoietic toxicity in idiosyncratic and dose-dependent forms was reviewed. The 7 cases of idiosyncratic haematopoietic reactions associated with topical chloramphenicol reported in the literature are refutable evidence for the existence of such a response. In Scotland, despite extensive prescription of topical chloramphenicol, the incidence of acquired aplastic anaemia was found to be low, as were associated reports of blood dyscrasias throughout the UK. The epidemiology of acquired aplastic anaemia failed to make an association with topical chloramphenicol use. High-performance liquid chromatography (minimum detection limit 1 mg/l) was used to investigate whether serum accumulation of chloramphenicol occurred after topical therapy in 40 patients. The mean dose of chloramphenicol eye drops used after 1 week of treatment was 8.0 mg, and after 2 weeks, 15.3 mg. As expected, chloramphenicol failed to accumulate to detectable levels. This supported the view that topical chloramphenicol was not a risk factor for inducing dose-related bone marrow toxicity. Calls for the abolition of treatment with topical chloramphenicol based on current data are not supported.

Population-based cohort study of microbial keratitis in Scotland: incidence and features

OBJECTIVE

To investigate the incidence and features of bacterial, fungal and protozoal keratitis in Scotland.

DESIGN

Prospective, population-based cohort study of all persons who developed culture proven microbial keratitis over an 8 month period.

SETTING

West of Scotland, UK.

SUBJECTS

Approximately 3,000,000 population.

MAIN OUTCOME MEASURES

Incidence and risk factors for microbial keratitis.

METHODS

All patients were included who had presumed microbial keratitis from which bacteria, fungi or Acanthamoeba was isolated from the corneal scraping by the hospital laboratory using a standardised protocol. In addition, contact lens wearing patients with pathognomonic features of Acanthamoeba keratitis, who yielded a negative culture result when referred on chlorhexidine therapy, were included if Acanthamoeba could be cultured from their lens storage case.

RESULTS

The overall annual incidence of culture-proven microbial keratitis was 0.26 per 10,000 with a rate of 1.8 per 10,000 for contact lens wearers (all types, soft and rigid). Based on a previous pilot study of 'presumed' microbial keratitis in Glasgow, it was possible to estimate the incidence of expected 'presumed' microbial keratitis as 0.36 per 10,000 overall and 2.44 per 10,000 for contact lens wearers (all types). The incidence for Acanthamoeba keratitis was 1.49 per 10,000 soft contact lens wearers; this infection was not detected in the absence of contact lens wear nor with use of gas permeable or rigid contact lenses.

CONCLUSIONS

'Presumed' microbial keratitis from all causes, in the adult population, was approximately three times less common in the West of Scotland (0.36 per 10,000) than would be expected from a comparable retrospective study from Minnesota, USA for the years 1980-1988 (1.1 per 10,000). It was rare (approximately one case expected in 2 million per year) in the absence of pre-existing corneal disease, cosmetic contact lens wear or trauma. Ocular surface disease was the underlying cause predisposing to infection in 58% of cases, with an incidence of 'presumed' keratitis of 0.21 per 10,000 population; the highest incidence was found in the elderly population. Contact lens wear was responsible for 38% of cases, emphasising the importance of preventive hygiene and effective disinfection in this group. The estimated incidence of 'presumed' microbial keratitis in the West of Scotland associated with cosmetic wear (daily and extended use) of soft contact lenses was significantly less (P<0.05) than that expected from a prospective study in New England, America in 1985 (266 per 10,000, rather than 8.05 per 10,000). However, the estimated incidence for presumed microbial keratitis for the West of Scotland associated with wearing soft contact lenses for cosmetic purposes in the daily wear modality (266 per 10,000) was less, but not significantly less, than that found in the prospective American study (4.20 per 10,000). The daily wear mode for contact lenses is almost universal in the West of Scotland, where extended wear has never been recommended. Extended wear has been shown in the USA to be associated with an incidence of presumed microbial keratitis between five and ten times higher than that associated with daily wear. This explains the lower incidence we have observed and a difference with the US study for overall infection rates but not when associated with daily wear alone. The incidence of proven Acanthamoeba keratitis found in the Scottish study among wearers of soft contact lenses for daily wear cosmetic purposes was exceptionally high at 1.49 per 10,000.

Acanthamoeba keratitis in Scotland: risk factors for contact lens wearers

OBJECTIVE

To investigate risk factors for Acanthamoeba keratitis amongst contact lens wearers in Scotland.

DESIGN

Patients with Acanthamoeba keratitis in the Scottish study, all of whom wore contact lenses, were compared with 46 healthy asymptomatic contact lens-wearing controls. They were all visited at home for contact lens and environmental microbiological sampling. In addition, all 288 optical practices in the West of Scotland were polled for contact lens types and disinfecting solutions sold in 1995, and a sample, each of whom fitted more than 500 contact lenses per year, were polled for a second time. Independently, a poll was commissioned by the Eyecare Information Service in July/August 1995 to estimate the numbers of contact lens wearers in Scotland and the UK. Industry was polled for numbers of each contact lens disinfecting regimen sold in Scotland in 1995.

SETTING

West of Scotland, UK.

SUBJECTS

All contact lens wearers among the 3 million population of the West of Scotland Health Board Areas.

MAIN OUTCOME MEASURES

Risk factors for Acanthamoeba infection and recommendations for its prevention.

RESULTS

When Acanthamoeba infection occurred, patients' home water systems were frequently (54%) found to be colonised by this amoeba. Patients more frequently washed their storage cases in tap water than controls (P<0.05) with resulting contamination, kept storage cases wet rather than air drying them (P<0.05), and had coliform bacteria cultured from the storage case (P<0.05) and had viable Acanthamoeba within the storage case (P<0.0001). Overall, patients were found to have significantly more risk factors than controls (P<0.0001). The noncompliant use of chlorine tablet disinfection, or failure to disinfect contact lenses at all, was associated with increased risk (P<0.05). Ionic high water content contact lenses (FDA group 4 material), when used without disinfection or with non-compliant use of low chlorine (Soflab) tablet-based disinfection, were associated with increased risk of Acanthamoeba infection (P<0.05). In log-linear modelling of risky hygiene behaviours associated with contamination of storage cases with Acanthamoeba, the most significant behaviour was found to be use of the less effective disinfection methods (chlorine tablets or no disinfection). However further investigation showed that these methods were associated with an increased probability of rinsing the storage case in tap water, so that these two behaviours are confounded in the group studied.

CONCLUSIONS

Failure to disinfect contact lenses, non-compliant use of chlorine tablets and/or introduction of tap water rinsing of storage cases were associated with increased risk of Acanthamoeba infection. New multipurpose solutions and hydrogen peroxide gave the lowest risk of Acanthamoeba infection, with no statistically significant difference between them. Ionic high-water content (FDA group 4) contact lenses were at increased risk of being associated with Acanthamoeba keratitis if used without effective disinfection (multipurpose solutions or hydrogen peroxide). The use of domestic tap water for contact lens and storage case hygiene must be avoided, as a chain-of-causation' was identified from the home water supply.

The role of Pseudomonas aeruginosa biofilm in the attachment of Acanthamoeba to four types of hydrogel contact lens materials

PURPOSE

The effect of the previous coating of a contact lens surface with Pseudomonas biofilm on adsorption of Acanthamoeba onto four types of hydrogel materials was investigated.

METHODS

Hydrogel contact lens quarters from each of the four FDA groups of hydrogel materials were incubated for at least 12 h in a suspension of 10(7)/ml of Pseudomonas aeruginosa (ATCC 27853) to coat their surfaces with biofilm. After rinsing, the lenses were incubated for 90 min in 5 x 10(5)/ml of Acanthamoeba castellanii trophozoites. New, uncoated lens quarters were incubated in the Acanthamoeba suspension as controls. After rinsing, all adsorbed trophozoites on one surface of each lens quarter were counted by direct light microscopy. Adsorption was expressed as numbers of amoebae per square centimeter of lens surface, and nonparametric data analysis was performed.

RESULTS

Acanthamoeba adsorption to new, uncoated lenses was greater for ionic materials (groups 3 and 4) than for the nonionic materials (groups 1 and 2). Pseudomonas biofilm increased adsorption on all four lens types.

CONCLUSION

Pseudomonas biofilm enhanced adsorption of Acanthamoeba on all lens types studied, but the adsorption to nonionic materials was significantly less. This suggests that all lens wearers may be at increased risk for Acanthamoeba infection if lenses are previously contaminated with bacterial biofilm, but this risk may be reduced by the use of certain lens types (low water content, nonionic materials).

Confirmatory evidence from 18S rRNA gene analysis for in vivo development of propamidine resistance in a temporal series of Acanthamoeba ocular isolates from a patient

DNA sequences of three 18S rRNA gene alleles present in trophozoites obtained before and after therapy for Acanthamoeba keratitis substantiate a previous report that the infection was due to a single Acanthamoeba strain. Thus, the possibility that propamidine resistance which developed during therapy was due to a mixed infection was ruled out.

Antimicrobial management of presumed microbial keratitis: guidelines for treatment of central and peripheral ulcers

AIMS

To determine the quantitative relation between the major risk factors for microbial keratitis of previous ocular surface disease and contact lens wear and central and peripheral infiltration, often associated with ulceration, in order to establish a rational chemotherapeutic management algorithm.

METHODS

Data from 55 patients were collected over a 10 month period. All cases of presumed microbial keratitis where corneal scrapes had been subjected to microbiological examination were included. Risk factor data and laboratory outcome were recorded. Antimicrobial regimens used to treat each patient were documented.

RESULTS

57 episodes of presumed microbial keratitis were identified from 55 patients, 24 male and 31 female. There were 30 central infiltrates and 27 peripheral infiltrates of which 28 were culture positive (73% of central infiltrates, 22% of peripheral infiltrates). 26 patients had worn contact lenses of whom 12 had culture positive scrapes (9/14 for central infiltrates, 3/12 for peripheral infiltrates). 31 patients had an ocular surface disease of whom five previous herpes simplex virus keratitis patients developed secondary bacterial infection. Anterior chamber activity and an infiltrate size > or = 4 mm2 were more common with culture positive central infiltrates than peripheral infiltrates (chi 2 test = 11.98, p < 0.001).

CONCLUSIONS

Predisposing factors for "presumed" microbial keratitis, either central or peripheral, were: ocular surface disease (26/57 = 45.6%), contact lens wear (26/57 = 45.6%), and previous trauma (5/57 = 8.8%). Larger ulceration (> or = 4 mm2) with inflammation was more often associated with positive culture results for central infiltration. None of these four variables (contact lens wear, ocular surface disease, ulcer size, anterior chamber activity) were of intrinsic value in predicting if a peripheral infiltrate would yield identifiable micro-organisms. Successful management of presumed microbial keratitis is aided by a logical approach to therapy, with the use of a defined algorithm of first and second line broad spectrum antimicrobials, for application at each stage of the investigative and treatment process considering central and peripheral infiltration separately.

Has the introduction of multi-purpose solutions contributed to a reduced incidence of Acanthamoeba keratitis in contact lens wearers?: a review

This review paper considers hypotheses for the apparent reduction in incidence of Acanthamoeba keratitis over the last 2 years. Investigating such a reduction has been facilitated by the performance of an accurate measurement of the incidence of this infection amongst contact lens wearers in the West of Scotland at 1:6750 soft lens wearers annually in 1994 and 1995, the infection did not occur in wearers of rigid or gas permeable lenses nor in those avoiding wear of a contact lens. The reduction in frequency of presentation of this infection anecdotally in Scotland in 1996 and 1997 is supported by a retrospective survey in England, although this method of assessing incidence historically is open to error. A new survey by the Royal College of Ophthalmologists should, in due course, present another accurate incidence figure for 1997/98. The reason for the apparent decline in incidence of Acanthamoeba keratitis is believed to be due to the introduction by industry over the last 3 years of sterile multipurpose (cleaning and disinfecting) solutions (MPS) containing polyhexamethylene biguanide to achieve their current popularity. This situation is mirrored by that in the United States when the introduction of MPS is thought to have reduced their incidence rate of Acanthamoeba keratitis following the outlawing of contact lens storage in home made saline, using water contaminated with Acanthamoeba.

Colonization of transplant unit water supplies with Legionella and protozoa: precautions required to reduce the risk of legionellosis

Organ transplant recipients and other immunosuppressed patients are known to be at increased risk of nosocomial Legionnaires' disease. Although the ecology of Legionella in hospital water storage and distribution systems (including a protozoonotic relationship with free-living protozoa) has been well documented, little is known regarding the quality of water supplied to high-risk units. Hot- and cold-water samples (two first draw and one run to waste for 5 min) were taken from 69 (85%) of the 81 United Kingdom organ transplant units (31 renal, 24 bone marrow, nine cardiopulmonary and five liver transplant units) and cultured for Legionella and protozoa. Legionella spp. were isolated from the water supplies of 38 (55%) units and Legionella pneumophila from 31 (45%). The blue-white fluorescent group of Legionella (Legionella gormanii, Legionella bozemanii and others) was isolated from 18 (26%) units. Free-living protozoa were isolated from 47 units (68%) and genera of the protozoa known to permit the intracellular growth of Legionella (PGIGL), from 40 units (58%). Possible associations between Legionella and the variables Protozoa; PGIGL; water pH; and circulating water temperature (recorded after running to waste for 5 min) were examined by logistic regression analysis. In cold-water supplies, a significant association was found between the isolation of Legionella and PGIGL (P = 0.032; OR = 1.81; 95% CI 1.1-3.1). In hot-water supplies, an inverse association was found between the isolation of Legionella and circulating water temperature (P = 0.034; OR = 1.0719 per degree C; 95% CI 1.0052-1.1432). (We failed to isolate Legionella when the circulating hot water was > 58 degrees C. No other associations were significant. We recommend the active surveillance of water quality in high-risk patient areas, and that transplant units, either with a history of nosocomial Legionnaires' disease, or where active surveillance indicates a persistently high Legionella colony count, take remedial action. The quality of cold water may be improved by provision of a dedicated supply taken directly from the incoming mains; and of hot water by the use of a dedicated calorifier, able to maintain a minimum circulating hot water return temperature of 60 degrees C.

Effect of patient wear and extent of protein deposition on adsorption of Acanthamoeba to five types of hydrogel contact lenses

Attachment of Acanthamoeba species to hydrogel contact lenses is a possible route of infection in Acanthamoeba keratitis. In this study, Acanthamoeba adsorption was compared with extent of lens deposition in worn lenses of different hydrogel polymers. After wear, lenses (80 lenses of 5 different types) were analyzed for total protein, surface area of deposition, and Acanthamoeba castellani trophozoite and cyst adsorption. Adsorption of Acanthamoeba trophozoites to worn lenses was greater than adsorption to unworn lenses for four of the five lens polymers (p < 0.01). Adsorption of cysts was greater for one of the five lens polymers (p < 0.001); all other adsorption assays showed no change with wear (p > 0.05). Adsorption was affected by both the water content and ionicity of the lens polymer. These results show that adsorption of Acanthamoeba to worn hydrogel contact lenses is greater than or equal to adsorption to unworn lenses.

Influence of inoculum, medium and serum on the in-vitro susceptibility of coagulase-negative staphylococci to teicoplanin and vancomycin

The susceptibility to teicoplanin of 100 coagulase negative staphylococci, predominantly isolated from intravenous catheter tips and exit sites was determined by agar dilution on IsoSensitest media with and without the addition of 20% inactivated horse serum using an inoculum of 10(4) cfu/spot. Incorporation of serum resulted in a three-fold increase in the geometric mean MIC and a four-fold increase in the geometric mean MBC. Further tests, performed in DST and IsoSensitest medium supplemented with 20% inactivated horse serum, resulted in a wide variation in teicoplanin MICs with differences in the geometric mean MICs being up to 8.8-fold in serum media compared to unsupplemented media, whereas the MICs of vancomycin were unaffected. Under the various experimental conditions used, the susceptibility of the coagulase negative staphylococci to teicoplanin varied from 31-100%, while all were consistently susceptible to vancomycin. We therefore recommend that teicoplanin MICs be determined in the presence of serum as these are better related to serum drug levels and reflect more accurately the conditions in vivo. Trials of teicoplanin as monotherapy are required to provide further insight into the relationship between its in-vitro antibacterial activity and its clinical efficacy as the drug is easier to administer, better tolerated and less toxic than vancomycin which might compensate for its reduced activity in the presence of serum.

Acanthamoeba griffini. Molecular characterization of a new corneal pathogen

PURPOSE

Acanthamoeba was isolated from the cornea of a soft contact lens wearer who had keratitis. The protozoan was also isolated from the contact lens storage case and the domestic water supply used to clean the case. Using morphologic features, all three isolates were identified tentatively as A. griffini, a species not previously associated with keratitis. Complete small subunit ribosomal RNA gene (18S rDNA) sequence analysis was used to characterize further the three isolates.

METHODS

18S rDNA was polymerase chain reaction-amplified from whole cell DNA derived from amoebal lysates. The genes were cloned and sequenced. Complete sequences of approximately 2800 base pairs were obtained from each culture and compared wih those stored in a data base for homologous Acantamoeba sequences.

RESULTS

The isolates were unequivocally identified as A. griffini both by comparison of the gene sequence available for the type strain of the species and the presence of a unique group I intron located within the small subunit rDNA. Sequences obtained for the three isolates were identical, indicating that they were the same strain.

CONCLUSIONS

The first direct connection between human disease and A. griffini is reported from a case of Acanthamoeba keratitis. The type strain of this species was isolated from a marine environment, but the disease-causing strain ws isolated from a domestic water supply. The DNA sequences obtained confirmed unequivocally the epidemiologic association between a keratitis-causing strain of Acanthamoeba, the contact lens storage case, and the domestic water supply.

Amebic keratitis in a wearer of disposable contact lenses due to a mixed Vahlkampfia and Hartmannella infection

PURPOSE

To support the hypothesis that Acanthamoeba is not a unique cause of amebic keratitis, we report a case of amebic keratitis in which viable Acanthamoeba could not be isolated from corneal tissue. Vahlkampfia and Hartmannella, two other genera of free-living ameba, were isolated, however, using prolonged culture.

METHODS

A 24-year-old wearer of soft contact lenses had keratitis. Extensive histologic and microbiologic investigations were performed on corneal scrape, biopsy, and keratoplasty tissue. Contact lenses, storage case, and the home water supply, where contact lens hygiene was practiced, were examined for the presence of micro-organisms.

RESULTS

No viruses, pathogenic bacteria, or fungi were detected from corneal tissue samples. Amebae were observed using light and electron microscopy, but these could not be unequivocally classified using immunocytochemical staining. Viable Vahlkampfia and Hartmannella, but no Acanthamoeba, were isolated from the corneal biopsy sample. Indirect immunofluorescence with a range of polyclonal rabbit antisera raised against axenically cultivated stains of the three amebal genera was unhelpful because of cross-reactivity. A diverse range of micro-organisms was present within the storage case, including the three amebal species. Amebic cysts also were associated with the contact lens.

CONCLUSION

A mixed non-Acanthamoeba amebic keratitis has been identified in a wearer of soft contact lenses where lack of storage case hygiene provided the opportunity for the free-living protozoa Vahlkampfia and Hartmannella to be introduced to the ocular surface. When Acanthamoeba-like keratitis occurs, but where Acanthamoeba cannot be isolated using conventional laboratory culture methods, alternate means should be used to identify other amebae that may be present. Polyclonal immunofluorescent antibody staining was unreliable for generic identification of pathogenic free-living amebae in corneal tissue.

Epidemiology of Pseudomonas aeruginosa keratitis in contact lens wearers

This study evaluated the epidemiology of Pseudomonas aeruginosa keratitis in contact lens (CL) wearers; the relationships between CL storage case contamination and CL hygiene practice and between CL hygiene and the development of keratitis. Sixteen CL wearers with keratitis were compared with 44 asymptomatic controls. Lens hygiene practice was assessed and CL care materials, domestic water sites and endogenous sites were evaluated microbiologically. Poor CL hygiene was not associated with Ps. aeruginosa keratitis. There was an association between keratitis and bacterial contamination of the CL and storage case (P < 0.0005). Lens and storage case contamination were not significantly associated with poor hygiene. No domestic or endogenous source for Ps. aeruginosa was found. Causative organisms may be derived from other sources, but CLs and CL storage cases provide a favourable environment for Ps. aeruginosa colonization. Changing the CL care environment to one less favourable for Ps. aeruginosa may help to eliminate this problem.

Contact lens wear by hospital health care staff: is there cause for concern?

Microbial keratitis can occur in association with contact lens wear. The absolute risk of infection is low but may be enhanced as a consequence of increased exposure to potentially pathogenic microbes in a hospital setting. There is variation in risk depending on type of lens worn and its modality of use. Extended-wear lenses carry the greatest risk. Pseudomonas aeruginosa and Acanthamoeba are causes of potentially devastating ocular infections in contact lens wearers. The risk of these infections could be reduced by fastidious hygiene practice. Hydrogen peroxide disinfection is recommended when a storage case is included in the care regimen. This should be cleaned thoroughly and dried prior to disinfection and never exposed to tap water. Daily wear of one-day 'disposable' soft contact lenses or use of rigid gas permeable lenses is recommended for hospital staff. Contact lenses should be removed immediately and discarded or disinfected if the eye becomes contaminated and/or use of an eyewash is required.