TIJUANA, Mexico | Aid workers and humanitarian organizations shared concerns Thursday about the unsanitary conditions inside and around the sports complex in Tijuana where more than 6,000 Central American migrants are crammed into a space adequate for half that many people and where lice infestations and respiratory infections are rampant.

As cold rain fell, the dust that coated everyone and everything in the open-air stadium turned to mud Thursday, worsening the already miserable conditions. On one side of the complex, a mud pit developed where people took outdoor showers next to a line of foul-smelling portable toilets.

The one large wedding-style tent set up in the middle of a sports field and several smaller tents with a capacity for just a few hundred people were nowhere near adequate for the swelling number of migrants who keep arriving daily. The overwhelming majority of the migrants were camped in makeshift enclosures comprised of lashed blankets and sheets of plastic or flimsy tents. Another 200 people slept on sidewalks because they wer find space in the complex or decided it was more comfortable outside.

“The truth is there is no room there inside. We asked yesterday,” said Astrid Yajaira of Sonsonante, El Salvador, who spent the night with three friends on a sidewalk in front of a warehouse across the street from the stadium. She had a sore throat and had hoped to find shelter inside.

The United Nations children’s agency, UNICEF, said it was “deeply concerned” for the well-being of more than 1,000 migrant children waiting in Tijuana or still moving north through Mexico. According to local officials, of the more than 6,150 migrants at the shelter as of Wednesday, 1,068 were children.

“These children have limited access to many of the essential services they need for their well-being, including nutrition, education, psychosocial support and health care,” UNICEF said in a statement Wednesday. Making the situation worse, the agency’s workers had to remove the coloring books, crayons and few other materials they had for children late Wednesday, because the agency lost its space on a baseball field to the arrival of more migrants.

Mexico’s National Human Rights Commission also pleaded to the government to act Thursday, noting that the sports complex was only planned to house 3,500 migrants and now had nearly twice that many.

“It’s unmanageable,” said Edgar Corzo, who heads the commission’s migrant rights division. The overcrowding “can produce all kinds of infections, all kinds of things can spread and we have four cases of chicken pox. They are contained but it’s a risk.”

Miguel Angel Luna Biffano, a health volunteer with the Nazarene Church Compassion Ministries, which has been accompanying the caravan since the migrants crossed into southern Mexico, said his aid group was dealing with lice and nit infestations as well as many respiratory infections. In the tropical south they had mostly treated dehydration and feet damaged and blistered from walking hundreds of miles.

“The overcrowding here causes them to get into places where they shouldn’t like under the bleachers” where it’s filthy, Luna said. “There’s overcrowding and very few hygiene norms. … With the water and the cold there are going to be too many infections, a lot of fevers. There is going to be a need for antibiotics.”

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