Boston: Hurricane Katrina doubled the rate of serious mental illness in areas ravaged by the storm but the urge to commit suicide fell, partly because survivors bonded with each other, a Harvard-led study said.

Billed as the biggest mental health study yet after Katrina killed about 1,500 people along the Gulf Coast, the survey showed that 15 per cent of 1,043 survivors were diagnosed with a serious mental illness five to eight months after the storm.

That figure suggests about 200,000 people from Alabama, Louisiana and Mississippi face serious mental illness because of Katrina, with about a third suffering from post-traumatic stress syndrome and the remainder depression, said the study's lead researcher.

Nearly 85 per cent of the survivors faced a major financial, income, or housing loss.