HURRICANE KATRINA'S effect on the city of New Orleans has been much longer-lasting than most expected. Almost four years after the storm, a quarter of the population has never returned. A third of homes still lie empty, many decked with tarpaulins and with the flood-line still visible. Residential streets are lined with houses with collapsing porches, fallen plasterwork and hopeful For Sale signs. Less than half the city's public transport facilities have been restored, and the wheels on the city's famous street-cars, even the one named Desire, are still rusty.

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Most important, though the number of chronically sick in the city has risen sharply, medical services remain in tatters. Only 57% of the city's medical facilities have reopened, and tens of thousands of records have been lost. In St Bernard Parish, which once had two hospitals, there is now none. Charity Hospital, the main refuge for the poor and uninsured for more than 250 years, is shuttered and surrounded by wire fencing. Doctors, nurses and military personnel spent a month cleaning and decontaminating the first three floors in the weeks after Katrina, but the hospital remains closed. Last month a group of citizens launched a legal appeal for it to be reopened, claiming that corrupt officials are using it as an excuse to get access to federal relief funds. But the owners of the building want to sell it.

The Lindy Boggs Medical Centre became a symbol of the struggle for survival in the hot, dank days after the flood. A day after the levees broke, the generators in the hospital failed, knocking out ventilators, transfusion machines and fresh water supplies. Nineteen patients died. The hospital is now to become a shopping centre.

Even in hospitals that are functioning again, medical staff are in short supply and treatment has become riskier. Emergency-room medics complain of having to treat too many desperately ill patients simultaneously. This increases the chance of both mistakes and lawsuits. That fear has led some doctors who live in the city to commute to hospitals far outside New Orleans rather than work locally.

Even before the storm, Louisiana was the least healthy state in America. In the past few years, however, levels of sickness have risen sharply. Almost two-thirds of New Orleans residents now report chronic health problems, a 45% rise since 2006. The percentage of people suffering from mental difficulties, mostly depression, has tripled since then, and the suicide rate has doubled since 2005. For months thousands of people were housed in temporary trailers which were poorly ventilated and contained high levels of formaldehyde. In the houses which were left habitable, mould and spores grew during the many humid weeks when the city lacked electricity. As a result, respiratory and skin problems are rife.

Greater poverty is also a factor. Almost a fifth of New Orleans households now live below the federal poverty line ($22,000 a year for a family of four). Many people were unemployed for months after Katrina and, although the number out of work has fallen, the effects endure. An estimated 12,000 people are still homeless.

The situation is expected to deteriorate in the coming years. Nearly 20% of people are now without health insurance. One in four say the emergency room is their primary source of care and, as the recession bites, that proportion is growing. Plans for two new hospitals are mired in payment battles and preservation disputes, meaning neither will become operational until at least 2013. It is little wonder that one in five New Orleans residents say they are considering leaving.