Maureen Boost

Microbial contamination of contact lenses and lens care accessories of soft contact lens wearers (university students) in Hong Kong

Purpose:  This study aimed to examine the rates of microbial contamination, and identify contaminants associated with contact lenses and lens care accessories used by a group of young contact lens wearers.

The effect of a compliance enhancement strategy (self-review) on the level of lens care compliance and contamination of contact lenses and lens care accessories

Purpose:  The aims were to determine the level of compliance of contact lens wearers, to identify which procedures have highest levels of non‐compliance and to study the effectiveness of a compliance enhancement strategy on the level of compliance.

Microbial flora of tears of orthokeratology patients, and microbial contamination of contact lenses and contact lens accessories.

Purpose. The purpose of this study is to determine if there are changes in the ocular flora of overnight orthokeratology (ortho-k) patients, and the levels of contamination of their lenses and lens accessories, and to correlate compliance with levels of contamination. Method. Normal ocular flora of 41 subjects was determined twice before commencing ortho-k lens wear by culture of the lower conjunctiva. Further specimens were collected on six follow-up visits after beginning lens wear, as were samples from their lenses, cases, and suction holders. A questionnaire on lens care was administered after the fifth visit. Results. Three subjects provided conjunctival samples yielding Staphylococcus aureus on one occasion before lens wear, one being positive for this organism after beginning lens wear. Of 38 subjects yielding no growth or only normal eye flora before use, 28 remained free of ocular pathogens after beginning lens wear. Only four subjects had positive cultures on more than one occasion after lens wear. There was no significant difference in isolation levels of pathogens with lens wear (p = 0.423). Lens culture of 54% of subjects yielded no growth or normal flora only; lenses of 16 subjects yielded potential pathogens, including three subjects contaminated on more than one occasion. Lens isolates did not match the organisms transiently colonizing the eye. Lens case, the most frequently contaminated item, was associated with lens contamination (p < 0.001), the same organism being isolated from both items in 11 subjects. Lens suction holder was less frequently contaminated. Neither lens case nor suction holder contamination was associated with isolates from the eye. Reported good compliance correlated with lack of contamination in all but one subject. The most frequent breaches in the lens care protocol were failure to clean, disinfect, and replace the lens case. Conclusion. Ocular flora was not altered by ortho-k lens wear over an extended period, and patients remained free of infection. Contaminants identified were generally of a transient nature. Most patients had significant contamination of at least one item, most frequently the lens case. Lens case isolates were significantly associated with those from the lens. The majority of patients reporting good compliance had low or no contamination of their lenses and accessories.

Colonization of Butchers with Livestock-Associated Methicillin-Resistant Staphylococcus aureus

Reports have documented colonization of swine in Europe, North America and more recently in China with livestock‐associated methicillin‐resistant Staphylococcus aureus (LA‐MRSA). Contamination of pig farmers, veterinarians and abattoir workers with these strains has been observed. However, although contamination levels of 10% of retail pork were reported from the Netherlands and Canada, there are limited data of contamination rates of workers handling raw meat. We investigated the rates of MRSA contamination of local butchers working in wet markets, where recently slaughtered pigs are cut up. Nasal swabs collected from 300 pork butchers at markets throughout Hong Kong were enriched in brain heart infusion broth with 5% salt and cultured on MRSASelect®. Isolates were confirmed as Staphylococcus aureus and susceptibility testing performed. The presence of mecA was confirmed, SCCmec and spa type determined and relatedness investigated by PFGE. Subjects completed a questionnaire on MRSA carriage risk factors. Seventeen samples (5.6%) yielded MRSA, 15 harbouring SCCmec IVb. Ten strains were t899 (CC9), previously reported from local pig carcasses. Five strains were healthcare associated: SCCmec type II, t701(CC6), colonizing two subjects at the same establishment, and single isolates of t008 (CC8), t002 (CC5) and t123 (CC45). The remaining isolates were t359 (CC97), previously reported from buffaloes, and t375 (CC5), reported from bovine milk. None of these butchers reported recent hospitalization or a healthcare worker in the family. Two had recently received antibiotics, one for a skin infection. Four reported wound infections within the last year. All were exposed to meat for >9 h per day. Carriage of MRSA was higher in butchers than in the general community. Although five strains were probably of healthcare origin, the high incidence of t899 (CC9) suggests that cross‐contamination from pork occurs frequently. Washing of hands after touching raw pork is advised.

Isolation of Methicillin-Resistant Staphylococcus aureus (MRSA) from Retail Meats in Hong Kong

OBJECTIVES The presence of methicillin-resistant Staphylococcus aureus (MRSA) on meat purchased from retail outlets may allow its spread to households and represents a risk for colonization and possibly infection of consumers. Improved isolation methods have indicated that more than 10% of samples are positive. We aimed to determine rates of MRSA contamination of meat samples, including comparison of fresh and frozen samples. We characterized isolates and determined their antibiotic susceptibility. METHODS Samples of raw meats commonly consumed in Hong Kong were investigated for MRSA contamination using a double-enrichment isolation method. Isolates were characterized by antibiotic susceptibility testing, presence of mecA, SCCmec type, staphylococcal enterotoxins, Panton-Valentin leukocidin (PVL), and spa type. Differences in rates of MRSA contamination between meat types, rearing method, locations, sources, and fresh or frozen storage were compared. RESULTS MRSA was recovered from 21.9% of pork samples (78/355), 6.8% chicken (31/455), and 4.4% of beef (17/380). Isolation was considerably higher from fresh pork (47%) than frozen (0.6%), whereas contamination rates in fresh (6%) and frozen (7%) chicken were similar. All strains were multidrug resistant. All contaminated fresh pork and most frozen chicken originated from China. Most isolates belonged to CC9, being SCCmec IVb and spa type t899 or closely related spa types, but one chicken sample yielded ST398. Five strains carried spa types associated with human isolates. The egc enterotoxin group was present in the majority of isolates, but PVL in only three from chicken. CONCLUSIONS The predominance of t899 in isolates indicates that the primary source of contamination may be pig carcasses, previously demonstrated to frequently harbor CC9-positive MRSA in Hong Kong and China. The high rates of meat contamination suggest that improvements in food safety and personal hygiene guidelines may be advisable to reduce risk of spread of these MRSA strains in the community.

Detection of methicillin-resistant Staphylococcus aureus using a gold nanoparticle-based colourimetric polymerase chain reaction assay.

We report the use of gold nanoparticles (Au NPs) for direct colourimetric polymerase chain reaction (PCR) detection of methicillin-resistant Staphylococcus aureus (MRSA) in clinical specimens. The colourimetric assay comprised of 2 Au NP probes functionalized with Staphylococcus aureus 23S rRNA- and mecA-specific oligonucleotides. In this study, 72 clinical samples were tested, which included positive blood culture (n=23), urine (n=8), respiratory samples (n=23), as well as wound swabs, pus and body fluid (n=18). Results were recorded qualitatively by direct visual examination and quantitatively by UV-vis spectrophotometry. Using conventional bacterial culture as the gold standard, the sensitivity, specificity, positive predictive value and negative predictive value of this colourimetric assay were 97.14%, 91.89%, 91.89% and 97.14%, respectively, which were comparable to that of commercial real-time PCR assays with a lower cost per reaction. Our assay also showed good agreement with bacterial culture (κ=0.889). The overall detection limit was 500 ng target amplicon, which was comparable to or better than other similar Au NP biosensors. Interestingly, our data revealed the possible relationship between Au NP probe-target hybridization site and assay performance, which might provide hints for design of the Au NP biosensors for nucleic acid detection. To conclude, our study was the first report on the use of Au NP colourimetric assay for direct detection of MRSA in various types of clinical specimens. Further evaluation of the assay is needed in large-scale trials which can also allow for some modifications to streamline the procedures for routine use.

Detection of acanthamoeba in tap water and contact lens cases using polymerase chain reaction.

Purpose. To detect the presence of Acanthamoeba in Hong Kong tap water and the contamination of contact lens cases using a polymerase chain reaction (PCR) method. Methods. Tap water was collected from the bathroom sink of 100 households in Hong Kong and tested for the presence of Acanthamoeba by means of PCR amplification. Characteristics of homes were noted with respect to age, building type, and location. A sample of 100 contact lens cases were collected from regular users of contact lenses and tested for the presence of Acanthamoeba by PCR. Results. Ten percent of water samples were contaminated by Acanthamoeba. The risk for contamination was higher in older properties, those located in the urban area of Kowloon, and those in which the bathroom tap was served by a water tank. Only one contact lens case yielded Acanthamoeba. The subject admitted poor compliance with lens care routines. Conclusions. Levels of Acanthamoeba detected using PCR were somewhat higher than previously reported in Hong Kong. Older plumbing and poorly maintained water storage tanks may increase the risk of Acanthamoeba contamination. Poor compliance with care of the lens case, allowing for the build up of biofilm may increase the risk of Acanthamoeba contamination of the case and possible Acanthamoeba keratitis.

Non-compliance and microbial contamination in orthokeratology

Purpose. To determine the rates of microbial contamination of solutions and lens accessories of existing ortho-k lens wearers and the effect on contamination rates of monthly replacement and warnings. To investigate self-reported levels of compliance with care of the lenses and lens accessories and correlation of these levels with the rates of microbial contamination. Methods. Asymptomatic ortho-k lens wearers with at least 6-month successful use were requested to bring their lenses, solutions, and accessories to their next aftercare visit. All items, except the lenses, were replaced at each data collection visit. Samples collected from the lens surface, solution, and accessories were cultured for pathogens. These procedures were repeated twice at 1-month intervals. At the first visit, each subject and/or parent was interviewed about the care/use of the lens and accessories. Results. Thirty-eight subjects completed the study. Initial contamination rates of the lenses, lens cases, and tweezers were 29, 34, and 46%, respectively. Rates of contamination dropped for lenses, suction holders, and tweezers during the three-visit intervention. Contact lens solutions, except lens cleaner were contaminated on all occasions with the most contaminated product being artificial tears [33% (n = 18)]. There was no improvement in the contamination rate of the lens cases. The most common pathogens isolated were Staphylococcus aureus and Serratia marcescens. Compliance was lowest for care of lens cases and highest for care of lenses. However, correlation between reported compliance and presence of pathogens failed to reach significance. Conclusions. Subjects’ awareness of the importance of lens cleanliness is high and can be improved by regular reinforcements. However, attitudes toward cleaning of accessories was far less satisfactory and while replacement and warnings resulted in significant improvements of contamination rates of tweezers and suction holders, more emphasis should be placed on educating patients on correct care of lens accessories.

Occupational exposure to raw meat: A newly-recognized risk factor for Staphylococcus aureus nasal colonization amongst food handlers

Staphylococcus aureus contaminating raw meat may increase nasal colonization risk for occupationally-exposed food handlers. Food handlers from six catering establishments were nasally sampled for S. aureus and completed a questionnaire on carriage risk factors. Isolates were characterized for antibiotic susceptibility, spa type and, for methicillin-resistant strains, SCCmec type. Of 434 food handlers, 99 (22.8%) were colonized with S. aureus. Five isolates were methicillin-resistant belonging to SCCmec IV (2) and V (3). Resistance to tetracycline (20%), and erythromycin (16%) was high, but <10% to other antibiotics. Spa typing revealed 17% of isolates as t189, with 8% each t127 and t1081. Food handlers ever handling raw meat had a significantly higher colonization risk (OR=2.7; 95% CI: 1.7-4.5), increasing to 3.7 (95% CI: 2.0-6.8) for those always exposed. This is the first report of increased colonization risk in food handlers exposed to raw meat. This occupational hazard may increase infection risk, so improved compliance with workplace hygiene may be required.

Cytotoxicity and effects on metabolism of contact lens care solutions on human corneal epithelium cells

Purpose:  The aim was to determine the cytotoxic effects of three multipurpose solutions (MPS) on human corneal epithelial cells (HCEC) and to assess the metabolic rates of recovering cells at different levels of cell membrane damage.