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Acanthamoeba Keratitis in Soft-Contact-Lens Wearers

Within a 9-month period from mid-1985 to February 1986, CDC received reports of 24 cases of Acanthamoeba keratitis, a much higher number than previously reported during similar time periods. Twenty (83%) of the patients wore contact lenses. Of these, two wore hard lenses (one hard, the other rigid gas-permeable); four wore extended-wear lenses; and 14 wore daily-wear soft lenses. Between July and October 1986, CDC performed a case-control study of soft-contact-lens wearers to identify the risk factors associated with Acanthamoeba keratitis (1).

Patients were selected for the study from persons with Acanthamoeba keratitis reported to CDC before August 1986 and who wore soft contact lenses, had onset of keratitis symptoms after June 1985, and had species of Acanthamoeba isolated from corneal smears or biopsy and/or demonstrated in stained corneal scrapings or tissue. Controls were selected from the files of the ophthalmologist or optometrist originally prescribing contact lenses for the patient and were matched with the patient by general contact-lens type (daily-wear soft contact lenses (DWSL) or extended-wear soft contact lenses (EWSL)), age (plus or minus 5 years), and city of residence.

CDC personnel used a standardized telephone questionnaire to obtain information from patients and controls on the specific brands of contact lenses and associated solutions they used, their routine lens-cleaning procedures, and their behavioral activities. To study the prevalence of Acanthamoeba and other microbial contaminants, investigators asked controls to submit contact-lens solutions and lens-care hardware* to CDC to be examined for contamination with Acanthamoeba, bacteria, and fungi (2,3). Similar materials were not available from patients because they had not been wearing their lenses for as long as 12 months.

Twenty-seven patients with Acanthamoeba keratitis and 81 uninfected, matched controls were interviewed. The 27 patients resided in 12 states**. All of the patients had onsets of symptoms between June 1985 and June 1986, with no seasonal predilection. Twenty patients (74%) and 59 controls (73%) wore DWSL. The remainder in both groups wore EWSL. There was a significantly higher proportion of males among patients than among controls (14/27 (52%) compared with 14/81 (17%), odds ratio*** (OR) = 7.25, 95% confidence interval (CI) = 2.53-20.76).

Patients were significantly more likely than controls not to disinfect their lenses as frequently as recommended by lens manufacturers (18/25 (72%) compared with 26/81 (32%), OR = 5.83, CI = 2.22-15.32). Significantly more patients than controls used homemade saline solutions, instead of commercially prepared saline solutions**** (21/27 (78%) compared with 14/81 (17%), OR = , CI = -). Because most persons using homemade solutions used them for several purposes, no distinction could be made as to whether a particular usage was more likely to be associated with infection than other usages. No association was noted between any of the commercially prepared contact-lens solutions or contact lenses and infection.

Patients were significantly more likely than controls to wear their lenses while swimming (17/27 (63%) compared with 24/81 (30%), OR = 6.24, CI = 1.90-20.46). This association remained statistically significant after controlling for sex. Patients were not more likely than controls to place their lenses in their mouths, wear their lenses in a hot tub, or report an injury to the eye.

Seventy-two (89%) controls submitted at least one specimen for microbiologic study. All solutions and hardware had been previously opened and used by the participant. All of the 11 homemade saline specimens submitted were colonized with bacteria and fungi. Eight (73%) showed relatively high levels of contamination ( greater than or equal to 105 colony-forming units (CFU) of bacteria and fungi per milliliter). Acanthamoebae were isolated from two of these: A. hatchetti, from one, and A. polyphaga, from another. In contrast, only one (2%) of the 59 commercially prepared saline specimens was contaminated with bacteria or fungi, and none were contaminated with Acanthamoeba. Fluid samples from 56 (69%) of the 81 specimens of lens-care hardware had positive bacterial/fungal assays; 46 (57%) had titers between 105 and 108 CFU/ml. Acanthamoebae were isolated from three specimens. No disinfectants, daily cleaners, or eye drops/lubricants were contaminated with bacteria, fungi, or Acanthamoeba. Reported by: Div of Parasitic Diseases, Hospital Infections Program, Div of Host Factors, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Acanthamoeba keratitis is a serious infection of the cornea caused by amoebae of the genus Acanthamoeba. Including the patients reported here, less than 100 persons have been diagnosed as having Acanthamoeba keratitis in the United States since the disease was first described in 1973 (4-15). The mechanism by which Acanthamoeba infects the human cornea is unknown. Studies using animal models have been largely unsuccessful in establishing an infection comparable to that in humans. Historically, the infection has been associated with penetrating corneal trauma (4,7,9,12,14). More recently, an association with contact-lens wear has become apparent (8-13). However, a few patients have had neither a history of trauma nor of contact-lens wear (1,6,12).

The risk factors identified in this study suggest deviations from contact-lens wear and care procedures recommended by lens manufacturers and health-care professionals. Current U.S. Food and Drug Administration licensure of commercial salt tablets (used to make homemade saline solution) applies only to using the saline solutions before and during thermal disinfection of lenses, not as a postdisinfection rinse or wetting agent. Laboratory studies show that thermal disinfection of soft contact lenses is effective in killing Acanthamoeba trophozoites and cysts (15), suggesting that use of homemade saline solutions before and during the thermal disinfection phase is safe. This study was not able to epidemiologically evaluate the risk of using homemade saline solution for a specific lens-care activity because most persons using homemade solutions used them both before and after disinfection. However, it should be noted that 70% of patients and only 17% of controls used such solutions after disinfection.

In interpreting the results of this study, several potential biases should be considered:

  1. Cases and controls may have been overmatched.

  2. Patients had not been wearing their contact lenses for up to 12 months before the interview; therefore, they may have had difficulty in remembering the details of the care of their contact lenses.

  3. Marketing data suggest that only 28% of soft-contact-lens wearers in the United States are male (a proportion significantly higher than that in the control group) (Dorland and Sweeney, unpublished data). Therefore, the control group may have been biased toward including more women than men. The former may have been more easily contacted by their ophthalmologist or optometrist and may have been more likely to consent to participating in the study.

  4. Finally, the contact-lens solutions and associated hardware were not collected in a controlled manner. Although Acanthamoeba keratitis is relatively rare, risk factors

associated with the infection among soft-contact-lens wearers may also apply to more common bacterial infections of the cornea. Persons wearing contact lenses should be reminded to adhere closely to recommended contact-lens wear and care procedures. These include using sterile solutions after disinfecting lenses, using solutions and disinfection methods appropriate for the specific lens type, cleaning and disinfecting lenses each time they are removed, and hand washing before handling lenses. Ophthalmologists and optometrists should explain carefully the recommended cleaning and wearing procedures and should review these recommendations with their patients periodically. Contact-lens wearers not complying with these recommendations may be increasing their risk for infection with Acanthamoeba and other organisms. As a result, they could develop partial or total loss of vision. However, further studies are necessary to determine the magnitude of the risk.


  1. CDC. Acanthamoeba keratitis associated with contact lenses--United States. MMWR 1986;35:405-8.

  2. Busta FF, Peterson EH, Adams DM, Johnson MG. Colony count methods. In: Speck ML, ed. Compendium of methods for the microbial examination of foods. Washington, DC: American Public Health Association, 1984:62-83.

  3. Visvesvara GS. Laboratory diagnosis. In: Rondanelli EG, ed. Amphizoic amoeba: human pathology. Padova, Italy: Piccin Nuova Libraria, 1987:201-23.

  4. Visvesvara GS. Free-living pathogenic amoeba. In: Lennette EH, Balows A, Hausler WJ Jr, Truant JP, eds. Manual of clinical microbiology. 3rd ed. Washington, DC: American Society for Microbiology, 1980:704-8.

  5. Jones DB, Visvesvara GS, Robinson NM. Acanthamoeba polyphaga keratitis and Acanthamoeba uveitis associated with fatal meningoencephalitis. Trans Ophthalmol Soc UK 1975;95:221-32.

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