A lack of sanitation threatens to create killer diseases in the vast refugee camps where hundreds of thousands of earthquake survivors have crammed in together, relief officials said Saturday, as the need for latrines increasingly joined food and water and shelter as major concerns.

Just one portable toilet serves about 2,000 people in a sprawling camp across from the collapsed National Palace, forcing most to use a gutter next to where vendors cook food and mothers struggle to bathe their children.

"We wash the vegetables first from water brought in by trucks, but a lot of times the water isn't clean," said Marie Marthe, 45, cooking a large pot of collard greens, carrots and goat as flies gathered on her daughter's diaper. "We don't have any choice."

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With homes across the capital reduced to rubble, survivors have crammed tightly into plazas and other open spaces — so tightly that it is hard to find a place to dig latrines. "In some parks there is no physical space," said UNICEF's coordinator for water and sanitation, Silvia Gaya.

"As of yesterday we were in the process of digging latrines for about 20,000 people," Gaya said, adding that 1,100 squatting platforms were arriving Saturday, to be distributed in camps and covered with plastic sheeting for privacy.

Nearly three dozen organizations are joining in a U.N.-led effort to build latrines and handle solid waste disposal, said Dr. Jon Andrus, deputy director of the Pan American Health Organization. Authorities also plan to build more permanent resettlement camps with plumbing and sewage and have identified some locations.

The results of these efforts aren't yet evident in many places.

"I haven't seen sanitation at any of the camps," said Dr. Louise Ivers, Haiti clinical director for Partners in Health. She fears "a mass outbreak of measles, which would really be potentially devastating for a camp where there are 10,000 people living."

Medical workers are also worried about tetanus, as well as dengue and malaria, both mosquito-borne diseases.

Few tents have been supplied to the quake's survivors, exposing people to the elements. Signs begging for help in English — not Haitian Creole — dot nearly every street corner in Port-au-Prince.

It could take weeks to get the 200,000 tents needed for Haiti's homeless, said Marie-Laurence Jocelyn Lassegue, the culture and communications minister. Haiti now has fewer than 5,000 donated tents and coordinating the aid operation remains a problem.

Some Haitians are so fed up with the camps that they are making a risky return to their destroyed homes — often the only semblance of property they have left.

"The situation is only getting worse," said Josielle Noel, 46, who was among dozens of people pooling their labor to start rebuilding in the concrete slum of Canape Vert, an area devastated by the Jan. 12 quake.

Tired of waiting for government help, the families lugged heavy bundles of wood and tin up steep hillsides to start rebuilding new homes on top of old ones.

"Even if it's unsafe, I can't imagine leaving. Even if the government helps, it will come too late. This is how it is in Haiti,"said Noel Marie Jose, 44, whose family was reinforcing crumbling walls with tin and wood in Canape Vert.

Surrounding her, concrete homes were either crushed or had toppled down a hill. Jose and other families said they were worried both about the coming rainy season and fear they may lose their plots after demolitions because they either lack clear title or the government does not want them to rebuild on land it considers unsafe.

Reconstruction, resettlement and land titles are all priorities of the government of President Rene Preval — but so far in name only.

The government has been nearly paralyzed by the quake — its own infrastructure, including the National Palace, was destroyed — and so far it has been limited to appeals for foreign aid and meetings with foreign donors that have yet to produce detailed plans for the emergencies it confronts.

Its first priority is moving people from areas prone to more quakes and landslides into tent cities that have sanitation and security but have yet to be built. Preval held dozens of meetings with potential outside contractors to discuss debris removal, sanitation and other long-term needs.

About 200,000 people are in need of post-surgery follow-up treatment and an unknown number have untreated injuries, said Elisabeth Byrs, an official of the U.N.'s humanitarian coordination office. But she said sanitation is increasingly a major concern.