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Investigation FAQs

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.