Acanthamoeba keratitis: the role of domestic tap water contamination in the United Kingdom.
OBJECTIVE
The incidence of acanthamoeba keratitis (AK) in the UK is some 15 times that in the United States and seven times that in Holland. To investigate reasons for this higher frequency, a study of the role of domestic tap water as a potential source of AK was undertaken.


METHODS
Tap outlets from the homes of 27 patients with culture-proven AK were sampled and cultured for free-living amoebae (FLA). For all Acanthamoeba isolates, mitochondrial DNA (mtDNA) restriction fragment length polymorphisms (RFLPs) and cytochrome oxidase (cox 1/2) sequence typing was performed to determine the similarity between corneal and tap water isolates.


RESULTS
FLA, including Acanthamoeba, were isolated from 24 (89%) of 27 homes, and the presence within the homes varied significantly with tap water temperature and location: 19 (76%) of 25 bathroom sink cold taps sampled compared with 6 (24%) of 25 hot and 9 (47%) of 19 kitchen cold taps compared with 3 (16%) of 19 of hot kitchen taps. Acanthamoeba were isolated from 8 (30%) of 27 homes (five bathroom sink cold taps, one cloakroom cold tap, one bath, and one bedroom sink mixer [hot/cold] taps). In six cases, identical Acanthamoeba mtDNA profiles were found for the clinical and home tap water isolates. In keeping with UK plumbing practice, 24 of 27 homes had internal roof water storage tanks to supply domestic taps, but the mains fed the kitchen cold tap.


CONCLUSIONS
Water storage tanks promote colonization of domestic water with FLA, including Acanthamoeba, and hence increase the risk of AK. This accounts for the significantly greater incidence of AK in the UK and supports advice to avoid using tap water in contact lens care routines.
Kilvington
Simon
S
Department of Microbiology and Immunology, University of Leicester, Leicester, United Kingdom. sk46@le.ac.uk
Gray
Trevor
T
Dart
John
J
Morlet
Nigel
N
Beeching
John R
JR
Frazer
David G
DG
Matheson
Melville
M
D000048:Acanthamoeba / Q000235:genetics / Q000302:isolation & purification*; D015823:Acanthamoeba Keratitis / Q000453:epidemiology* / Q000469:parasitology; D000818:Animals; D004272:DNA, Mitochondrial / Q000032:analysis; D016054:DNA, Protozoan / Q000032:analysis; D003576:Electron Transport Complex IV / Q000235:genetics; D004866:Equipment Contamination; D006801:Humans; D012150:Polymorphism, Restriction Fragment Length; D012189:Retrospective Studies; D011795:Surveys and Questionnaires; D006113:United Kingdom / Q000453:epidemiology; D014867:Water / Q000469:parasitology*; D014881:Water Supply
D004272:DNA, Mitochondrial; D016054:DNA, Protozoan; D014867:Water; D003576:Electron Transport Complex IV