Acanthamoeba contact lens danger analysed

Despite frequent disregard of contact lens hygiene recommendations and an abundance of Acanthamoeba spp. in local drinking water, contact lens wearers in Madrid, Spain, appear to be avoiding keratitis, researchers say.

In a study analysing the presence of the organism in contact lenses, only one in 177 participants reported keratitis.

"[W]e can assume that CL [contact lens] solutions are properly disinfecting the CL, since only 1.1% of the positive PCR [polymerase chain reaction] samples correspond to viable amoeba," wrote Thiago dos Santos Gomes of Universidad San Pablo CEU, Monteprincipe, Madrid, Spain, and colleagues in PLOS One.

The number of cases of Acanthamoeba keratitis has increased rapidly in the past two decades, the researchers write. And previous research has shown that people who wear contact lenses run a risk of keratitis, particularly if they fail to comply with recommended cleaning and disinfection procedures.

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Studies of contact lenses and their containers have found a wide range of contamination rates depending on geography and the method used to isolate organisms. Rates have ranged from 1% in Hong Kong to 10% in Iran.

The rate in the Canary Islands stands out among the locations studied, with a "surprising" 65.9% contamination rate, the researchers wrote. Environmental studies have found Acanthamoeba concentrations of up to 59% in tap water and 40% in sea water there.

Since Madrid has a 93.8% incidence of Acanthamoeba in treated water, the researchers wanted to know if it was also contaminating contact lenses and putting the wearers at risk of infection.

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They collected discarded contact lenses and cases from 177 healthy participants in Madrid and administered a hygiene habits questionnaire to them. They extracted DNA from about 200 microlitres of contact lens solution. They used a TaqMan real-time PCR to detect Acanthamoeba and two other common keratitis organisms, Pseudomonas aeruginosa and Staphylococcus aureus, from the DNA samples.

Of the contact lens wearers, 70% were female, 98% wore the soft variety of contact lenses, 88% wore their lenses daily, and 54% reported that the lenses caused them some discomfort. Nine of the 177 participants failed to return a questionnaire.

Risk factors for infection

A large proportion of the respondents reported some behaviours considered risk factors for infection. Specifically, 43% reported using their lenses longer than recommended, 41% reported occasionally showering while wearing the lenses, 32% did not change the solution in the cases daily, 29% did not clean the lens cases, 22% sometimes rinsed the lenses with tap water and 21% sometimes failed to wash their hands before handling their lenses.

The real-time PCR detected the DNA of Acanthamoeba in 87 of the 177 samples (49%). There was no significant difference in the contamination of contact lenses between male and female participants. Nor was there a statistically significant difference according to the hygiene habits of the users.

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Of those who reported failure to clean their lens cases, 61% had contamination with Acanthamoeba versus 29% of those who cleaned their cases. This correlation approached statistical significance (P = 0.062).

The researchers also performed a real-time PCR to detect the two most common species associated with microbial keratitis, P. aeruginosa and S. aureus. They did not find any statistically significant association between the presence of these organisms and hygiene habits, but they found that Acanthamoeba was more likely to be present in the absence of P.aeruginosa.

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The researchers also cultured contact lenses and their solutions on non-nutrient agar plates seeded with inactivated E. coli. They were only able to cultivate amoeba on one sample (0.6% of the total samples.)

The owner of this contact lens was a female who reported wearing her contact lenses longer than recommended, not washing her hands before handling her contact lenses, and sometimes rinsing her contact lenses with tap water or showering while wearing them. She also said she felt some eye discomfort, a possible indication of the presence of an organism such as Acanthamoeba, bacteria or fungi.

Among all the participants, the researchers didn't find any statistically significant correlation between eye discomfort and any of the hygiene habits. Once again, not washing contact lens cases came the closest; of the 49 people who failed to wash their cases, 31 (63.3%) had eye discomfort. And of those, 20 (64.5%) had Acanthamoeba DNA on their lenses (P = 0.073).

Suffering from keratitis, conjunctivitis

The researchers followed up with the 87 participants on whose contact lenses they detected Acanthamoeba. Forty-two of these participants responded with information about their ocular health since they joined the study. Only one of them reported suffering from keratitis, while a few others said they had suffered from conjunctivitis. The participant who reported keratitis declined their offer to determine whether her infection was caused by Acanthamoebae.

The 0.6% incidence of cultivatable Acanthamoebae in the Madrid contact lenses contrasts with a 65.9% incidence in the Canary Islands. The researchers speculated that the difference could be attributed to the warm climate and dust in the Canary Islands.

The researchers noted that methods for cultivating Acanthamoeba have a sensitivity of about 50%, which could account for the discrepancy between the cultivation results and the PCR results. It's also possible that some Acanthamoebae died of starvation between the last use of the contact lenses and the time when the researchers attempted to cultivate the organisms, they point out.

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In concluding, they highlight the correlation between not washing lens cases and evidence of contamination. Although the correlation didn't quite reach statistical significance, they recommended that lens wearers need to pay more attention to this protocol.

Specifically, lens wearers should rub the cases with a clean finger and a fresh multipurpose disinfecting solution for 5 seconds, rinse them with a fresh solution, wipe them with a tissue and air-dry them face down on a tissue for 6 hours, they said.

Finally, the researchers point out that the results of this study should not be interpreted to mean that the other lens hygiene practices they investigated are safe to ignore.