CHICAGO, Illinois (Reuters) -- Bausch & Lomb Inc.'s global recall of a popular contact lens solution in May appears to have stopped the spread of a serious eye infection but U.S. scientists still don't know what caused the outbreak, according to a study released on Tuesday.
Researchers at the U.S. Centers for Disease Control and Prevention do not believe improper lens hygiene practices alone are enough to explain the recent rash of cases of fusarium keratitis.
"We feel pretty confident that the outbreak is over," said CDC researcher Benjamin Park, who has studied the outbreak since the first reports of the infection in the United States in early March.
The rare but potentially blinding eye infection prompted Bausch & Lomb to halt shipments of its ReNu with MoistureLoc lens solution to U.S. retailers in April. Bausch issued a global recall of the product in May and earlier this month slashed its 2006 earnings forecast.
Clusters of infection were first reported in Singapore and Hong Kong earlier this year and the product was pulled from those markets in February.
Park and colleagues at the CDC in Atlanta conduced a study to determine the specific activities, hygiene practices and products associated with the infection, which appeared in the Aug. 23-30 issue of the Journal of the American Medical Association.
As of June 30, the researchers had identified 164 confirmed cases of patients infected with the fungal infection fusarium keratitis. Of those, 94 percent, or 154 patients wore soft contact lenses.
Infected patients came from 33 states and one U.S. territory and about 34 percent of them required a corneal transplant.
According to the study, infected contact lens wearers were 20 times more likely than to have used Bausch & Lomb's ReNu with MoistureLoc lens solution than another solution.
Park said the CDC is continuing to monitor reports of the infection in multiple states and said the threat to the nation's 34 million contact lens wearers is very small.
The study, which looked at samples of the solution from the factory, warehouse, returned bottles and other samples, concluded that the infection was not present in the solution, but most likely came from external sources, such as the users' home.
But the study said lax hygiene could not have caused the outbreak. "It definitely was not poor contact lens hygiene alone," Parks said.
He did note that a number of patients with the infection had reused old solution left in the contact lens case and warned against that practice.