From December 14, 1987, through January 19, 1988, an outbreak of epidemic keratoconjunctivitis (EKC) caused by type 8 adenovirus occurred at a large ophthalmology clinic in California.* A telephone survey of a systematic sample of patients treated at the clinic during that outbreak indicated that 17 (17%) of 102 had new onset of four or more symptoms compatible with EKC (conjunctival redness, swelling or redness of the eyelid, discharge from the eye, sticking together of eyelids, pain or discomfort in the eye, photophobia, or a foreign-body sensation) within 3-30 days of visiting the clinic. An additional 46 patients who had onset of EKC after visiting the clinic were identified by review of clinic records. Eye cultures were obtained from 60 patients; 29 were positive for adenovirus 8.

To examine risk factors for acquiring EKC in the clinic, a case-control study was conducted to determine patient characteristics and exposures to various procedures, equipment, and clinic personnel. Cases were clinic-acquired EKC infections in the 63 identified patients. Controls were the 85 patients from the telephone survey who had not developed EKC after visiting the clinic.

Case-patients and controls were similar in age and sex. Based on univariate analyses, risk for EKC was associated with exposure to pneumatonometry (odds ratio (OR)=13.3; 95% confidence interval (CI)=5.1-31) and exposure to three different caregivers, one of whom was a technician who frequently performed pneumatonometry. After controlling for exposure to pneumatonometry, only exposure to a single caregiver remained associated with the risk of acquiring EKC (OR=11.7; p less than 0.01, Fisher's exact test). Sixty-seven percent of case-patients had a documented exposure to pneumatonometry or to this caregiver.

Control measures implemented on January 19, when the outbreak was first recognized, included discontinuing use of the pneumatonometer, reinforcing "strict" handwashing procedures, and furloughing clinic employees with signs or symptoms of EKC. A telephone survey of 54 patients who visited the clinic from January 19 to January 26 indicated that one patient had developed symptoms compatible with EKC.

Before the implementation of control measures, the pneumatonometer tip was disinfected with 70% isopropyl alcohol; other tonometers and other instruments were disinfected with sodium hypochlorite solution. A telephone survey of six other eye clinics in the state indicated those clinics used isopropyl alcohol to disinfect pneuma tonometer tips. The instruction manual distributed by the manufacturer of the pneumatonometer directed users to "sterilize" the tip by dabbing it with a 50% isopropyl alcohol pad. Reported by: D Koo, MD, P Courtwright, DrPH, AL Reingold, MD, School of Public Health, Univ of California, Berkeley; SB Werner, MD, GW Rutherford, MD, State Epidemiologist, California Dept of Health Svcs. RE Lippman, OD, TJ Lowe, MPH, Center for Devices and Radiological Health, Food and Drug Administration. Hospital Infections Program, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: In addition to this outbreak, adenovirus 8 has been implicated as the cause of EKC outbreaks in other ophthalmology clinics (1-4). In this report, exposures to pneumatonometry and to one health-care worker were epidemiologically linked to cases. The identification of these two risk factors suggested several mechanisms of virus transmission during the epidemic, including inadequate handwashing by health-care personnel between patient contacts and inadequate disinfection of the pneumatonometer between uses on patients' eyes.

As with many types of nosocomial infections, person-to-person transmission of adenovirus 8 occurs primarily through hands of personnel and/or other persons in contact with patients (1-8). Therefore, handwashing between patient contacts is the most effective measure for preventing transmission of this microorganism (8). When contact with infective secretions is expected (e.g., when patients have obviously infected conjunctivae and/or during an outbreak of EKC), health-care personnel should routinely wear fresh gloves for, and wash hands after, each contact with a patient and/or eye secretions (8).

Previous reports have identified contact tonometry (i.e., the process of measuring intraocular pressure using an instrument that directly indents or flattens the patient's cornea) as a risk factor for EKC (4-6). In general, contact tonometry in these cases was performed with either the Schiotz tonometer or the crystal-tipped applanation tonometer. In contrast, the pneumatonometer (a contact tonometer that contacts and applanates the patient's cornea with air pressure through a silicone-rubber membrane; it is distinct from the "puff" noncontact tonometer used by optometrists) has been associated with only one previous nosocomial EKC outbreak (7).

Problems regarding disinfection or sterilization of the tips of the Schiotz indentation tonometer or the crystal-tipped applanation tonometer have been well characterized (e.g., after each patient use, these instruments must be disassembled to allow adequate cleaning and disinfection of the instrument tip and adjacent parts) (9-12). In contrast, for disinfection of the pneumatonometer and other types of tonometers, health-care workers have had to rely on the instrument manufacturer's recommendations printed in the product instruction manual. The exact basis of these recommendations is unknown, although they may have been derived from studies on the disinfection of the older types of tonometers (9-12) or from standard in vitro assays that have assessed the susceptibility of bacterial and viral indicator strains to the action of germicides (13,14). However, tonometers vary in design and material composition; therefore, disinfection or sterilization procedures that are appropriate for one type of tonometer may not be suitable for another (9-11). In addition, the in vitro conditions and interaction between test strains and germicides may not simulate in vivo conditions. For example, the test strains, adenoviruses 2 and 7, were susceptible to alcohols after 10 minutes of contact time (14), but adenovirus 8 was resistant to the action of 70% isopropyl alcohol (12).

Because of the differences in tonometer design and uncertainties regarding disinfection, manufacturers of tonometers and other medical instruments used on the eye should consider 1) designing instruments that can be cleaned and disinfected or sterilized easily, preferably without disassembly, between uses on patients, 2) carefully testing disinfection or sterilization procedures for their products under use-conditions and by using appropriate test microorganisms, and 3) clearly outlining the tested procedures in user manuals. Manufacturers' instructions to users should also emphasize that disinfection or sterilization of instruments that contact the eye should be done after each patient use (15) and that adequate disinfection or sterilization cannot be achieved if the instruments are not initially cleaned thoroughly of any organic material that can impede contact between the germicide and the target microorganism(s) during the disinfection or sterilization process (15,16).

In the absence of controlled studies specifically on disinfection or sterilization of the pneumatonometer and other tonometers, the tips of such tonometers should be routinely cleaned, then disinfected or sterilized after each patient use. The tip can be cleaned with soap and water or with another cleansing agent suggested by the manufacturer and disinfected by soaking for at least 10 minutes in a solution containing 500-5000 ppm chlorine (e.g., a 1:100-1:10 dilution of household bleach) or in any commercial germicidal solution that is registered with the Environmental Protection Agency as a "sterilant" and is compatible with the tonometer (12,15-17). The soaking time in commercial germicides necessary to achieve high-level disinfection (which includes inactivation of adenovirus type 8 and other viruses and bacteria that are pathogenic to the eye) varies by type and concentration of solution and should be indicated by the germicide manufacturer on the product label (15,16).

In addition to effective cleaning and disinfection or sterilization, other ancillary procedures have been necessary to control nosocomial EKC outbreaks. These measures decrease the opportunity for direct or indirect contact between infected and uninfected persons, and include 1) cohorting of EKC-infected health-care personnel only with patients known to have EKC, 2) preventing infected personnel from having direct patient contact for up to 14 days following onset in affected personnel, and 3) using unit-dose eye solutions (2,5-7). Control of large epidemics or those that occur in association with a community outbreak of EKC have required more stringent measures, such as triaging patients and assigning those suspected of being infected to waiting and examining rooms that are separate from those for uninfected patients and admitting into the clinic only emergency cases, while postponing examination/treatment of elective patients until after the outbreak ends (2,4,5,7).

The Food and Drug Administration is reviewing the labeling of tonometers and other devices that contact the eye and will be considering labeling modifications, taking into consideration the above recommendations. Physicians are requested to report clusters of eye infections occurring in patients of ophthalmology clinics through their state health departments to the Epidemiology Branch, Hospital Infections Program, Center for Infectious Diseases, CDC; telephone (404) 639-3406.

References

1. Wegman DH, Guinee VF, Millian SJ. Epidemic

keratoconjunctivitis. Am J Public Health 1970;60:1250-7.

2. Buehler JW, Finton RJ, Goodman RA, et al. Epidemic keratoconjunctivitis: report of an outbreak in an ophthalmology practice and recommendations for prevention. Infect Control 1984;5:390-4.

3. Reilly S, Dhillon BJ, Nkanza KM, et al. Adenovirus type 8 keratoconjunctivitis--an outbreak and its treatment with topical human fibroblast interferon. J Hygiene 1986;96:557-75.

4. D'Angelo LJ, Hierholzer JC, Holman RC, Smith JD. Epidemic keratoconjunctivitis caused by adenovirus type 8: epidemiologic and laboratory aspects of a large outbreak. Am J Epidemiol 1981;113:44-9.

5. Ford E, Nelson KE, Warren D. Epidemiology of epidemic keratoconjunctivitis. Epidemiol Rev 1987;9:244-61.

6. Barnard DL, Hart JCD, Marmion VJ, Clarke SKR. Outbreak in Bristol of conjunctivitis caused by adenovirus type 8, and its epidemiology and control. Br Med J 1973;2:165-9.

7. Warren D, Nelson KE, Farrar JA, et al. A large outbreak of epidemic keratoconjunctivitis: problems in controlling nosocomial spread. J Infect Dis 1989;160:938-43.

8. Garner JS, Simmons BP. Guideline for isolation precautions in hospitals. Atlanta: US Department of Health and Human Services, Public Health Service, CDC, 1985; DHHS publication no. 83-8314.

9. Clarke SKR, Hart JCD, Barnard DL. The disinfection of instruments and hands during outbreaks of epidemic keratoconjunctivitis. Trans Ophthalmol Soc U K 1972;92:613-8. 10. Wood RM. Prevention of infection during tonometry. Arch Ophthalmol 1962;68:202-18. 11. Corboy JM, Goucher CR, Parnes CA. Mechanical sterilization of the applanation tonometer. Pt 2. Viral study. Am J Ophthalmol 1971;71:891-3. 12. Nagington J, Stehall GM, Whipp P. Tonometer disinfection and viruses. Br J Ophthalmol 1983;67:674-6. 13. Morton HS. Alcohols. In: Block SM, ed. Disinfection, sterilization, preservation. Philadelphia: Lea and Febiger, 1983:225-39. 14. Klein M, Deforest A. Principles of viral inactivation. In: SM Block, ed. Disinfection, sterilization and preservation. Philadelphia: Lea and Febiger, 1983:422-34. 15. Garner JS, Favero MS. Guideline for handwashing and hospital environmental control. Atlanta: US Department of Health and Human Services, Public Health Service, CDC, 1985; DHHS publication no. 99-1117. 16. Favero MS. Sterilization, disinfection and antisepsis in the hospital. In: Manual of clinical microbiology. 4th ed. Washington, DC: American Society for Microbiology, 1985:121-31. 17. CDC. Recommendations for prevention of HIV transmission in health-care settings. MMWR 1987;36(no. 2S). *This article is adapted from Infection Control and Hospital Epidemiology 1989;10:547-52.

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