U.S. District Judge Kurt Engelhardt ruled that a batch of lawsuits on behalf of hundreds of plaintiffs against the federal government and several trailer manufacturers can't be handled as a class action because each person's claim is unique and must be examined individually.

Government tests found elevated levels of formaldehyde in many of the trailers that housed victims of Katrina and Rita after those powerful hurricanes clobbered the Gulf Coast in 2005. Formaldehyde is a preservative that can cause breathing problems and is classified as a carcinogen.

Lawyers for the storm victims accuse trailer makers of using shoddy materials and building methods in a rush to meet the government's demand for emergency housing for the displaced. The attorneys had argued that a class-action lawsuit would efficiently resolve all the cases from Louisiana, Texas, Mississippi and Alabama that Engelhardt is presiding over in New Orleans.

But the judge said the cases involve hundreds of trailer models made by dozens of companies and occupied by people with varying medical histories and symptoms.

"Each plaintiffs' claims and alleged injuries will require an examination of individual evidence," Engelhardt wrote in a 50-page ruling.

Tony Buzbee, one of the lead lawyers for plaintiffs, said he respects the judge's decision but hasn't ruled out an appeal.