2007 Outbreak Investigation FAQs
Acanthamoeba Keratitis Case Information FAQs
How was the nationwide increase in cases detected?
In 2006, the Illinois Department of Health contacted CDC to report an increase in AK cases in Illinois that were under investigation by the University of Illinois at Chicago. In January 2007, CDC initiated a retrospective survey of 22 ophthalmology centers nationwide to assess whether cases of AK had been increasing in the United States over the past 8 years. In March 2007, data received from 13 of these centers demonstrated an increase in culture-confirmed cases of AK beginning in 2004 with a wide geographic distribution. On March 16, 2007, CDC initiated a multi-state investigation to look for risk factors associated with this increase in AK cases.
How many people with AK have been identified?
As of June 25, 2007, CDC had received reports from public health authorities and ophthalmologists in 37 states and Puerto Rico identifying 221people with AK, of whom 158 became ill on or after January 1, 2005 and tested positive for Acanthamoeba by cultures taken from corneal specimens. In-depth interviews with 102 people with culture-confirmed AK have been completed.
How many people with AK are enrolled in this study?
As of June 25, 2007, 102 people with culture-confirmed AK have been enrolled in the study and interviewed. CDC and its partners are now working to obtain and verify data from these people as well as to collect information from a group of people without AK living in the same neighborhoods as AK patients. The information collected from this group of people without AK will be used for comparison purposes in the final data analysis.
How is information being collected on people with AK?
Standardized telephone interviews of people with AK, their treating ophthalmologists, and their primary eye care providers are being conducted by state and local health officials and staff at CDC. For comparison purposes in the final analysis, similar information is being collected from people without AK living in the patients’ neighborhoods. Laboratory testing at CDC of clinical specimens, contact lenses, bottles of solution, and contact lens cases received from people with AK, including genetic typing of Acanthamoeba, is ongoing.
Where are these cases occurring?
Nationwide. As of June 25, 2007, people with AK have been identified in 37 states and Puerto Rico.
Who are the people with AK?
Among the 102 people with culture-confirmed AK who were interviewed and evaluated in a preliminary analysis on June 25, 2007, the median age was 31 years (range: 12—76 years); 21 (21%) were aged <18 years. Sixty-four (63%) were female.
How much eye damage has occurred in people with AK?
Of the 76 patients for whom clinical data were available on June 25, 2007, medical therapy for AK was unsuccessful for 20 (26%). These 20 people were required or expected to undergo corneal transplantation.
Do most people with AK wear contact lenses?
Yes. Of the 102 people with AK included in a preliminary analysis on June 25, 2007, 79 (77%) wore soft contact lenses, 10 (10%) wore rigid lenses, 1 (1%) wore hybrid lenses, and 12 (12%) reported no contact lens use.
How many people get AK each year?
AK is a rare disease and information about incidence is limited because AK cases are not required to be reported to CDC. In general, we estimate that only one to two cases of AK per million contact lens users occur each year in the United States, based on an analysis of cases identified during an outbreak of AK during 1985–1987. With an estimated 30 million people in the United States wearing soft contact lenses, this would equate to approximately 30 to 60 cases of AK per year. Information about the previous AK outbreak investigation can be found on the Publications, Data, & Statistics page.
Note: AMO Complete® MoisturePlus™ multipurpose cleaning solution will be referred to as AMOCMP in this section.
What institutions are involved in this investigation?
Several groups are collaborating on this investigation. Partners include CDC, health departments from 37 states and Puerto Rico, the Food and Drug Administration, the U.S. Environmental Protection Agency, ophthalmologists from Baylor University, consultants from the University of Illinois at Chicago, and other health partners.
What has the investigation found so far?
Preliminary analysis of the data collected as of May 24, 2007 indicated a strong association between the development of AK in soft contact lens wearers and the use of Advanced Medical Optics (AMO) Complete® MoisturePlus™ multipurpose solution for soft contact lenses. Repeat analysis on June 25 using more complete data strongly indicated the same association.
What is the evidence to implicate AMOCMP in this outbreak?
Analysis of data on June 25, 2007 revealed that people with AK who used soft contact lenses were at least 16 times more likely to have used AMOCMP compared with a group of healthy adult soft contact lens users. Among the 102 people with AK assessed at this time, 79 were soft contact lens users, and 75 reported using some type of contact lens solution. Of these, 45 people (60%) reported some use of AMOCMP in the month before symptom onset; more than half (41 people; 54%) reported using AMOCMP as their primary solution and more than one third (35 people; 47%) reported using AMOCMP as their only solution.
Although the analyses on both May 24, 2007 and June 25, 2007 were preliminary, CDC believes that the strength of the association between the use of AMOCMP and the development of AK among soft contact lens users warranted public health intervention. Therefore, in the interest of public health, the information was made public before the completion of the investigation. CDC and the Food and Drug Administration (FDA) have taken steps to notify the public and the medical and public health communities of this association and the manufacturer has voluntarily recalled this product.
Does AMOCMP cause AK?
It is more likely that AMOCMP allows AK to occur. AK is caused by a microscopic ameba called Acanthamoeba, which is commonly found in the environment and can infect the transparent outer covering of the eye (the cornea). When Acanthamoeba infects and damages the cornea, people develop AK. AMOCMP is intended to kill microorganisms that can infect the eye. However, preliminary analysis suggests that AMOCMP is associated with the development of AK. The exact mechanism for this association is as yet unknown but the association exists. Therefore, in the interest of public health, Advanced Medical Optics (AMO) voluntarily removed AMOCMP from the market and CDC and the Food and Drug Administration (FDA) are working closely with the manufacturer to collect additional information and to continue to alert and advise consumers as more information becomes available.
Is AMOCMP contaminated?
We don’t think so. There is no evidence at this time to suggest that bottles of AMOCMP are contaminated. As of June 25, 2007, AMOCMP lot numbers were available for 21 people with AK who reported using this solution; no single lot number was repeated. In addition, the observed increase in AK cases began in 2004 and is still ongoing, suggesting that contamination is unlikely to be the problem. Further laboratory testing will continue, however.
Are other contact lens solutions associated with AK?
No, not at this time. The preliminary analyses of the reported use of other brands of contact lens solution did not reveal any significant associations.
Are there any other risk factors for AK identified in this investigation besides AMOCMP?
In the preliminary analyses, multiple types of contact lens solutions and contact lenses were assessed but only AMOCMP emerged as a significant risk factor. However, the investigation is ongoing and investigators are continuing to evaluate these products as well as other potential risk factors such as hygiene, trauma, exposure to water, and past medical history.
Is tap water or any type of water treatment associated with this outbreak of AK?
No, not at this time. On preliminary analyses, there is no evidence to suggest that tap water or any specific types of water treatment provided by municipal water supply companies (e.g. , chloramine or chlorine) are significant risk factors in this outbreak. CDC investigators are asking patients to identify the water supplies they used in the month before symptom onset. Investigators are then following up with the relevant municipal water supply companies to determine the types of water treatment used. On preliminary analyses, the proportion of people with AK whose tap water supply was treated using chloramine instead of chlorine did not exceed that found for the general public.
To develop Acanthamoeba keratitis, people must first be exposed to Acanthamoeba. These amebae are common in nature and can be found in all areas of the environment, including water (e.g. , tap water and recreational water), soil, sewage systems, cooling towers, and heating/ventilation/air conditioning (HVAC) systems. Even with exposure to Acanthamoeba, the ability of these microorganisms to infect the cornea in healthy people is limited and AK is a rare occurrence. This outbreak is the result of one or more factors increasing the risk of infection beyond the usual risk of exposure to the amebae in the environment. Preliminary analyses of the data suggests that the primary risk factor is the use of AMOCMP by soft contact lens wearers.
Why was a preliminary investigation conducted before all the people known to have culture-confirmed AK were interviewed?
On May 24, 2007, CDC investigators began the analysis of the first 46 completed patient interviews to assess whether people with AK seemed to share any risk factors for developing AK. Early knowledge of the risk factors most likely contributing to the outbreak allowed CDC to better focus its investigation and take appropriate action to protect the public health. A subsequent analysis was performed on June 25, 2007 to assess whether the findings changed with the inclusion of more people with AK. No change in risk factors was identified. CDC and its partners are now working to obtain and verify data from study participants with and without AK as part of a final analysis of the data.
Now that the findings from the preliminary analysis have been publicized and AMOCMP has been voluntarily recalled, why is CDC continuing to investigate?
The investigation is far from over. Continuing the investigation will allow us to better define the scope of the outbreak, provide a more definitive assessment of the risks associated with use of contact lenses or lens-care products, possibly identify other risk factors, and allow CDC and its partners to develop and refine evidence-based recommendations to prevent further eye infections with Acanthamoeba.
What should contact lens users do to decrease their risk of developing AK?
- Check their medicine cabinet for AMOCMP. If they find it, stop using the product immediately. Contact the company at 1-888-899-9183 for instructions on what to do with unused solution;
- discard all soft contact lenses used with AMOCMP;
- discard all contact lens storage cases used with AMOCMP; and
- consult their eye care provider about choosing an alternative contact lens solution.
Furthermore, they should visit their eye care provider if they experience any signs of eye infection, including eye pain or redness, blurred vision, sensitivity to light, sensation of something in the eye, or excessive tearing.
What are the general guidelines for soft contact lens use?
All contact lens users should follow established guidelines to help reduce the risk for eye infections, including AK. They should:
- Visit your eye care provider for regular eye examinations.
- Wear and replace contact lenses according to the schedule prescribed by your eye care provider.
- Remove contact lenses before any activity involving contact with water, including showering, using a hot tub, or swimming.
- Wash hands with soap and water and dry before handling contact lenses.
- Clean contact lenses according to instructions from your eye care provider and the manufacturer’s guidelines.
- Never reuse or top off old solution. Use fresh cleaning or disinfecting solution each time lenses are cleaned and stored.
- Never use saline solution or rewetting drops to disinfect lenses. Neither solution is an effective or approved disinfectant.
- Be sure to clean, rub, and rinse your lenses each time you remove your lenses. Rubbing and rinsing your contact lenses will aid in removing harmful microbes and residues.
- Store reusable lenses in the proper storage case.
- Storage cases should be rubbed and rinsed with sterile contact lens solution (never use tap water), emptied, and left open to dry after each use.
- Replace storage cases at least once every three months.
Contact lens users with questions regarding which solutions are best for them should consult their eye care providers. They should also consult their eye care providers if they have any of the following symptoms: eye pain or redness, blurred vision, sensitivity to light, sensation of something in the eye, or excessive tearing.
- Page last reviewed: June 9, 2017
- Page last updated: June 9, 2017
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