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.
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.
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.