Contamination Risk of Reusing Daily Disposable Contact Lenses

Abstract

Purpose. 

This study investigated contamination of saline and daily disposable contact lens (DDCL) stored overnight after use in the original blister pack and the practices of a group of DDCL users.

Methods. 

Twenty DDCL wearers placed their lenses after 1 day's use back into the blister pack saline (BPS) and left them overnight before transferring both lens and BPS to a new CL case. The lens and BPS were cultured the following day, and total number of organisms, Staphylococci, and gram negative organisms enumerated. Each subject submitted five pairs of lenses over a 1 month period.

Results. 

Ninety-five percent of subjects had at least one pair of contaminated lenses, and the BPS yielded similar results to the contaminated lenses, with staphylococcal contamination being predominant. Three subjects admitted to not washing their hands before handling their lenses and six to habitual reuse of their lenses with storage in the BPS. There was a higher risk of contamination in male subjects.

Conclusions. 

Reuse of lenses poses an important risk for DDCL users because they are unlikely to have received proper training in cleaning and disinfection of lenses and do not use a lens case or disinfecting solutions. Overnight storage in BPS results in contaminated lenses which if reused increases the infection risk especially with Staphylococci. It is important that practitioners carefully educate their patients in correct use of DDCL and, as cost of lenses is a major factor in willingness to reuse, ensure that DDCL is the most suitable choice when prescribing.

The use of daily disposable contact lenses (DDCL) has been steadily increasing since their introduction.^1–3 Of this CL wearing mode, teenagers represent the largest proportion of new patients in several countries.^2,4 Most patients who choose this mode of CL wear have cited convenience as the most important factor in their choice.^3,4 Another advantage is the possible health benefit because daily replacement avoids the need for regular CL care, and it was expected that the incidence of CL-related disease, including microbial keratitis (MK), would be reduced as a result of daily replacement.⁵ It has also been suggested that DDCL are more comfortable than biweekly or monthly disposable lenses, because a study indicated that 82% of CL wearers preferred DDCL compared with biweekly lenses,⁴ and there was a significant reduction in reports of discomfort and other symptoms in DDCL users.⁶ However, despite the positive aspects associated with DDCL, many wearers have rejected them as a choice because of their cost, despite the fact that, in many countries, annual cost of DDCL are similar to those of other CLs when all costs including disinfecting solutions are included.⁷ The expected reduction in infections in DDCL wearers has not been observed and this may be due to failure to comply with the regime.^5,8 Wearers reported extended wear of DDCL through one or more sleep cycles before removing, or wearing time exceeding the practitioners' recommended schedule.⁹ Studies have confirmed that overnight wear of CL increases the risk of MK.^10–13 More recently, an increased risk of MK was shown in overnight wearers of DDCL.¹⁴ Other issues of non-compliance with DDCL include inadequate hand washing⁹ and reusing the lenses.^1,15

Because reuse of DDCL appears to be a common non-compliant behavior, knowledge of the level of contamination of lenses that are kept overnight would be useful in helping practitioners to advise their patients against this practice. Although levels of contamination of CLs, lens cases, and other care accessories have been determined in previous studies,^16–24 there are no reports investigating contamination levels of DDCL kept overnight after use. DDCL wearers usually do not have a lens case because they do not need to purchase disinfecting solutions and for those who intend to reuse the lenses, they may store them inappropriately, for example leaving them overnight in the original blister packs with the initial solution. This study aims to evaluate the contamination rate of lenses stored overnight in blister packs after 1 day's use and to identify the microorganisms present. The wearing time and schedule and hand washing habits of the users were also investigated.

MATERIALS AND METHODS

Twenty DDCL wearers were recruited to participate in this study. All subjects were asymptomatic and had no history of ocular complications within the last 6 months. The subjects (10 females and 10 males) were aged between 19 and 22 years. Subjects completed a short interview to collect personal information and habitual lens wearing behavior. All subjects were given an information sheet and signed a consent form. The project was approved by the Human Subjects Ethics Committee of The Hong Kong Polytechnic University and complied with the tenets of the Declaration of Helsinki in 2002. Information collected included DDCL experience in years, brand of DDCL used, wearing time and schedule, reuse (if any), and lens handling procedures.

Samples

Each subject was given five packs, each containing a new pair of plastic forceps and a CL case. Subjects were asked to wear their own DDCL (see Table 1 for brands of lenses), handling the lenses as usual, and not to dispose of the blister packs and solution, but leave them in the place where they normally insert their lenses. The solution should be protected by the original foil cover. Subjects were instructed that, after use for only 1 day, the lenses were returned to the blister packs, covered with the original foil, and left overnight. No solution or saline should be added to the blister pack saline (BPS). The following morning, the BPS and lens were carefully transferred by the subject, using the forceps, into the CL case which was then closed tightly with the lids. The lenses and solutions were taken on the same day to the laboratory for analysis within 2 hours of collection. Each subject submitted five pairs of lenses over a 1-month period.

TABLE 1: Brands of lenses used by subjects

Microbial Culture

A 0.5 ml aliquot of the BPS was transferred from each lens case well to a bottle containing 4.5 ml of brain heart infusion broth. The broths were plated out without dilution and after a 1/10 dilution with normal saline. The dilutions were spread on duplicate nutrient agar plates using a sterile glass “hockey” stick. This media allowed for the growth of most non-fastidious organisms and was used for a total count of organisms present. The initial broth was also inoculated onto MacConkey agar (MAC), Mannitol salt agar (MSA), and Sabouraud dextrose agar (SDA). MSA is selective for Staphylococci, allowing growth of both Staphylococcusaureus and coagulase-negative staphylococci (CNS). MAC can support gram negative organisms and SDA for the growth of fungi. All plates, except SDA were incubated at 37°C for 24 h. SDA were incubated at 25°C for 2 weeks. The DDCL were removed from the lens case wells using sterile forceps and placed onto blood agar plates and gently pressed onto the surface. Blood agar can support the growth of most organisms including pneumococci. The plates were incubated at 37°C for 24 h. As a negative control, six new blister packs were opened and the lenses transferred to blood agar and the BPS cultured using the procedures described above.

The total numbers of colonies on the nutrient agar plates were counted using an automated counter (Acolyte Supercount, Symbiosis, Frederick, MD) and the dilution yielding a count between 30 and 300 colonies used to determine the number of organisms present in the original BPS. Organisms growing from the lenses on the blood agars were identified using standard methods.²⁵ Numbers of gram negative organisms present on MAC were recorded and the organisms identified. Similarly, numbers of staphylococci present on MSA were recorded and S.aureus identified using Staphaurex Plus (Murex Biotech, Dartford, UK). SDA plates were examined for the presence of fungi.

Treatment of Data

As sample size was small, non-parametric tests were used. Statistical analysis (SPSS, Version 17.0) was performed using chi-squared test and Mann-Whitney U tests as appropriate.

RESULTS

A total of 100 pairs of DDCL were collected from the subjects. The average lens wearing experience was 1.9 years for males and 2.1 years for females. Females wore their lenses for an average of 8.9 h and male subjects for 6.5 h daily. The average wearing schedule for males was 4.2 d/week and for females, 5.5 d/week (Table 2).

TABLE 2: Subject demographics and lens wearing history

Of the 200 BPS samples tested, 91 (45.5%) yielded growth. Twenty-five percent of positive samples contained more than 10⁵ colony forming units (CFU) per ml with 44% having 10⁴ to 10⁵ CFU/ml and 31% 10³ to 10⁴ CFU/ml. About 21% of positive BPS samples yielded staphylococci and 28% gram negative rods but no fungi were isolated (Table 3). Fresh BPS yielded no growth.

TABLE 3: Number of samples of BPS (n = 200) yielding growth after storage of a used contact lens overnight

Only one subject had no BPS contamination for all five pairs of lenses collected. Ninety-five percent¹⁹ of the DDCL wearers had contaminated lenses on at least one occasion; 15% with one pair contaminated, 5% with two, 25% with three, 15% with four, and 35% with all five pairs contaminated. Overall, 67% of lenses collected were contaminated. Of the subjects with all five pairs of lenses contaminated, five were males and two females. Males were significantly more likely to have contaminated lenses than females (chi squared, p = 0.03). Growth of BPS was significantly correlated with contaminated lenses (p = 0.001). Years of wearing DDCL, days per week of wear or hours per day of use were not significantly related to contamination of the lenses. Three subjects admitted to not washing their hands before inserting their lenses and six subjects (30%) to habitual reuse of their DDCL, with three reusing the same pair of lenses once, two twice, and one three times. The only subject with no contamination in any lenses or BPS collected reported hand washing before handling of lenses and no reuse of the lenses.

Organisms identified included S. aureus, CNS, Pseudomonas aeruginosa, and Klebsiella species. S. aureus was the most frequently isolated contaminant from both lenses and BPS, being present in 54% of contaminated lenses and 55% of contaminated BPS (Table 4). More than one species was isolated from 21% of lenses and 31% of BPS. Lenses from fresh packs yielded no growth.

TABLE 4: Number of isolates of organisms (%) from contaminated lenses after 1 day wear and from the saline in their blister packs after overnight storage (n = 134 lenses, 91 BPS)

DISCUSSION

This study has shown that the use of DDCL may result in infection risks if not used as intended by the manufacturer. To our knowledge, there has been no previous study on the level of contamination of a lens after 1 day of wear, nor of the risk of using the blister pack for overnight storage of lenses before reusing. After 1 day's wear, most lenses had microbial contamination including the presence of potential ocular pathogens, with 80% yielding growth on any one sample and 95% of subjects having at least one contaminated lens. Our definition of contamination was organisms being present on the lenses. Although CNS is unlikely to be harmful in most patients, the concept of DDCL is that lenses ready for use will not be contaminated. Although low levels of CNS may be considered normal and unlikely to cause infection, all contaminated BPS yielded at least 10³ CFU/ml, and so can be considered to have significant levels of contamination. There have been limited reports of contamination levels of DDCL, but it was recently reported to be lower than for other modalities.²⁶ It was interesting that one subject showed no growth from all lenses submitted as it would be expected that normal flora from the fingers (during removal) would contaminate the lens. It is possible that a combination of careful user (e.g., using alcohol wipes to clean fingers before removal), with a low level of normal ocular flora, and mild depositor may lead to low level of contamination, which may be inhibited by the high salt level in the BPS, resulting in no growth from the cultured lenses.

Although contamination of the lens should not be a problem if lenses are discarded after one use, as newly opened lens packs are sterile, but as this study showed, a high proportion of users are using them on multiple occasions. Reuse of lenses is worrying because wearers of DDCL receive no instruction on daily cleaning and are not provided with any accessories to allow them to perform daily cleaning, thus such deviation from recommended use may entail a high risk for infection. It was noted recently that DDCL wearers have a similar risk of MK compared with other lens- wearing modalities,⁵ and other studies have reported increased rather than the expected lower risks for this modality.¹⁰ An extreme case of non-compliance linked to sales of DDCL without any patient instruction was recently reported in which the subject developed bilateral Acanthamoebal ulcers.²⁷ It has been suggested that as the DD modality does not require the use of a lens case, this may reduce the risk of serious gram negative infection²⁸; but as reported here, poor compliance with the replacement schedule may contribute to increased infection risk. It would be interesting to determine levels of contamination after reuse, but it would not be ethical to ask subjects to reuse lenses. Our protocol required users to place a lens used only once back into the BPS. If lenses were reused it is likely that contamination levels would increase if cleaning of the lenses is not performed. In this study, the amount of BPS present when the lenses were submitted to the laboratory was usually enough for the lens to remain in its usual shape, although a few displayed distortion because of partial drying. As subjects were instructed not to add additional solution to the blister pack, it is unlikely that they reused the lenses for this study. Patients prescribed with DDCL may have less awareness of need or importance of hygiene and care. The package labeling of DDCL often states that the contents of the blister pack are sterile. This may give users a false sense of security, giving them the impression that reuse may be safe. It is a major concern that even though our subjects were all well-educated young people including some full-time students, a high percentage of them were willing to take the risk of reusing the lenses, in one case up to three times. The small sample size does restrict generalizability of our result and a further survey of DDCL users in Hong Kong would be useful to better determine reuse behavior. The willingness to reuse DDCL was also reported by 12 to 13% of subjects in surveys performed in Canada and United States,^15,29 most subjects citing saving money as the reason for reuse. As the subjects had been using the remaining contents of the blister pack for storage, it is important that practitioners do explain that the BPS is not a disinfecting solution and warn patients that this is not acceptable behavior. If cost is a major issue, practitioners should carefully consider the choice of lenses prescribed to avoid reuse to save money. However, for occasional users, for up to 3 d/week, the cost of DDCL use is similar to that of conventional lenses.⁷

Although several bacterial species grew from cultures of the lenses and BPS, no fungi were isolated. It is likely that saline allowed survival of bacteria but may have inhibited fungal growth.^30,31 Fungi would not have been unexpected because they have been shown to contaminate the eyes of CL wearers.³² Staphylococcal species are salt tolerant, which may explain their predominance among the isolates from BPS.³³ They are likely to have come from the hands and skin of the users.^34,35 There were more S. aureus than CNS isolated, although it could have been expected that CNS would predominate because these are usually the predominant organisms on patient-handled lenses. It is possible that the high-salt content in the BPS selected for S. aureus as this species is more salt tolerant than CNS. The actual salt concentration in each BPS after being opened for 24 h would vary depending on the temperature and humidity at the time as well as conditions in individual bathrooms. As CNS did grow from some samples, MSA was suitable for growth of those CNS surviving in the less concentrated BPS samples. In normal conditions of use, lenses will be contaminated by normal floral from the fingers on initial insertion. But, these levels of contamination will tend to be low if hands are washed properly before handling lenses and it is likely that this contamination would be transient and be washed away by lacrimation and blinking. In contrast, organisms attaching during the period of wear and contaminating the lenses after removal would have the opportunity to multiply or at least survive in the BPS. Although this study focused on the reuse of DDCL, another implication of our results is that if used lenses, whatever the replacement modality, are stored in saline and not in multi purpose solution, this is likely to increase the risk of infections. It is likely that some DDCL users store lenses in MPS and it was considered that the study should be extended to include this modality. However, we refrained from including this reuse modality because we felt that it could have encouraged incorrect use of DDCL.

It was disturbing to find that 3/20 admitted to not washing their hands before handling their CLs. Even though the majority of subjects reported washing hands before lens insertion, there was no observation of hand washing skill, time, or detergent use. Previous reports have shown that many patients do not wash hands correctly.^36,37 There was a higher rate of contamination in lenses of male subjects. This is reflected in higher rates of MK in male CL wearers.³² It is thought that females tend to be more aware of personal hygiene.^10,38 This was a small-scale study of 20 DDCL users, so it was not possible to examine the differences between lens materials on growth, but all five brands used in this study had at least one pair contaminated.

It is important that practitioners carefully discuss with their patients the advantages of DDCL, which are a simplified routine and a guaranteed clean, sterile, new lens every time if used correctly. Those patients who are willing to clean and reuse lenses would be better suited by other modes of wear (e.g., biweekly, monthly), especially if cost is a factor.

CONCLUSIONS

There is a high contamination rate of lenses if DDCL are reused after inappropriate storage. Thus, it is extremely important for practitioners to reinforce the need for compliance with daily replacement schedule for patients using this mode of lens wear. The high contamination rate of lenses including contamination with known ocular pathogens shows that reuse of DDCL involves a high and unacceptable risk of contamination of the eye and increased risk of MK.

ACKNOWLEDGMENTS

This work was supported by a grant for the Department of Health Technology & Informatics of the Hong Kong Polytechnic University.

Maureen Boost

Department of Health Technology

The Hong Kong Polytechnic University

Kowloon, Hong Kong

e-mail: [email protected]