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Tap water identified as source of U.K. bacterial keratitis cases
In a study, the majority of homes in which Acanthamoeba were isolated were occupied by a contact lens wearer.
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Certain household water storage systems used in the United Kingdom harbor free-living amoeba, including Acanthamoeba, U.K. scientists found. Further, their study showed a direct epidemiological link between the water storage units and the incidence of Acanthamoeba keratitis, particularly among contact lens wearers.
Dr. Simon Kilvington and colleagues at several institutions in the United Kingdom conducted the retrospective study, which sampled water from various taps in the homes of 27 patients with culture-proven Acanthamoeba keratitis.
According to the study, free-living amoeba (FLA) were isolated from at least one water sample from 24 of 27 (89%) homes. Of these, eight samples contained Acanthamoeba, and all were taken from taps supplied by roof storage cisterns.
Roof cisterns in the United Kingdom were used in the past to store water for times when the public water main was interrupted. They are used today mainly for supplying water to toilets and bathroom cold water taps, the authors wrote.
The authors noted that 23 of the study participants wore contact lenses, although none admitted to using such water for lens cleaning or storage, “suggesting that Acanthamoeba keratitis can arise from indirect exposure to contaminated tap water.”
“It is recommended that wearers adhere strictly to the manufacturer’s recommended lens hygiene procedures and use only sterile, approved solutions,” the authors said. “In addition … manipulation and storage of [contact lenses] … should take place away from sources of potential contamination.”
Tap water samples
According to the study, the incidence of Acanthamoeba keratitis in the United Kingdom is estimated to be between 17.53 and 21.14 per million — 15 times greater than in the United States and seven times greater than the rest of Europe.
In an attempt to explain this higher incidence, Dr. Kilvington and colleagues obtained water samples from hot and cold taps in various locations of participants’ homes. Samples were taken 3 to 10 months after the initial corneal culture was obtained from the patients.
The researchers then compared the Acanthamoeba samples isolated from the patients with the amoeba sample isolated from the taps. They also performed cytochrome oxidase sequence typing.
In addition, patients completed a questionnaire that evaluated possible sources of infection, including use and sanitation habits of contact lenses as well as the presence of a roof cistern.
Identical amoeba isolated
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According to the study, 24 of the 27 (89%) households had at least one tap test positive for FLA, but the presence of FLA varied significantly with water temperature and tap location.
Among cold water taps, nine of 19 (47%) kitchen taps supplied by public water mains tested positive for FLA compared with 19 of 25 (76%) bathroom taps (P < .05).="" among="" hot="" water="" taps,="" however,="" only="" three="" of="" 19="" (16%)="" kitchen="" taps="" and="" 6="" of="" 25="" (24%)="" bathroom="" taps="">P < .05)="" tested="">
Some bath water taps also cultured positive: five of 11 (45%) cold taps and two of 11 (18%) hot taps.
Among taps that mixed hot and cold water, two of seven kitchen taps were positive for FLA, as well as one of two bathroom sink taps, two of four bath taps and two of four shower taps.
According to the study, a variety of FLA were isolated from the water samples, with Acanthamoeba spp. found in eight of the 27 homes (30%).
In six of eight keratitis patients, mitochondrial DNA typing showed the patients had Acanthamoeba strains identical to the strains isolated from their household water sources.
Contact lens habits
Although no contact lens patients admitted to storing their lenses in tap water, all but three lens wearers reported that their lens storage cases or the lenses themselves did come into contact with tap water.
The authors note that seven of the eight homes in which Acanthamoeba were isolated were occupied by a contact lens wearer. Additionally, all had roof storage tanks.
FLA were isolated from water taps of the four patients who were not contact lens wearers, although only one sample was positive for Acanthamoeba. The authors note this patient had contracted his infection from mud splashed into his eye. The strain cultured from his cornea was not the strain isolated from his bath tap.
For Your Information:
- Dr. Simon Kilvington can be reached at Department of Infection, Immunity and Inflammation, Maurice Shock Medical Sciences Building, P.O. Box 138, University of Leicester, Leicester, LE1 9HN, United Kingdom; 44-116-252-2950; fax: 44-116-252-5030; e-mail: sk46@le.ac.uk.
Reference:
- Kilvington S, et. al. Acanthamoeba keratitis: The role of domestic tap water contamination in the United Kingdom. Invest Ophthalmol Vis Sci. 2004;45:165-169.