McALLEN, Texas — It was nearly 9 p.m., hours after the makeshift clinic for newly arrived migrants near the Mexican border in Texas was supposed to close, but the patients would not stop coming: A feverish teenager with a vile-smelling wound on his foot. A man with a head injury and bright red eyes. Children with fevers, coughs and colds.

Earlier in the day, a little girl named Nancy had been brought into the clinic with a cough and shaking chills. She had been vomiting, she said, and her spine hurt. An assistant took her temperature. “She’s got 104, almost 105,” she said.

The steady flow of migrants who arrived that night at the volunteer respite center operated by Catholic Charities here in the Rio Grande Valley had just been released by Customs and Border Protection after being apprehended near the border. The new arrivals had been in federal custody for up to 72 hours, but most had received no real medical attention — the volunteer physicians at the private clinic were the first doctors many had seen since crossing the border.

“He may lose that leg,” Dr. Martin Garza, a local pediatrician who works at the clinic every other weekend, warned the father of the teenager with the foot wound, handing him a course of antibiotics to take with him. “I cleaned it up as much as I could.”

An average of 2,200 migrants a day are now crossing the nation’s 1,900-mile border with Mexico, many after grueling journeys that leave them injured, sick or badly dehydrated. Yet most of the nation’s Customs and Border Protection facilities along the border lack sufficient accommodations, staffing or procedures to provide more than basic emergency care, a situation that has led to dangerous medical oversights.

Six adults died in CBP custody in the fiscal year ending in October, at least three of whom had a medical emergency shortly after being apprehended. Another, who had serious chronic diseases, died from health complications last month. In December, two migrant children — Jakelin Caal Maquin, 7, and Felipe Gómez Alonzo, 8 — died within three weeks of each other after showing signs of illness while being held and transported by Border Patrol agents in Texas and New Mexico.

A New York Times review of records and dozens of interviews with migrants, agents, researchers and health workers suggest that some of these deaths were not anomalies, but rather signs of entrenched problems that have repeatedly put detainees with medical conditions at risk.

At respite centers like the one in McAllen, Texas, that shelter migrants for a night or two after they are released from Border Patrol custody, doctors say the care provided by the agency has sometimes been so poor that they have had to send new arrivals straight to emergency rooms.

“They’re not treated as if their health and well-being is valued on any level,” said Dr. Anna Landau, a family medicine doctor who volunteers at a migrant shelter run by Catholic Community Services in Tucson, Arizona. “How do you send people who are clearly hurting, clearly in pain and suffering, how do you just move them through as if they’re just another number, as opposed to an actual human being?”

Migrants crossing the border from Mexico may be injured scaling barriers, in vehicle accidents, by gunfire or from nearly drowning. They may be suffering from dehydration, heat exhaustion or communicable illnesses — from influenza to chickenpox — that often spread in conditions of close confinement, though none so far have presented what health officials regard as an unusual or alarming public health or infectious disease threat. Some require medications for chronic diseases such as asthma, diabetes and high blood pressure.

Yet Border Patrol facilities until now have failed to provide comprehensive health screenings for those in their care. Medications — including lifesaving prescriptions for such conditions as asthma, heart disease and infant diarrhea — are routinely confiscated. Some migrants describe being left alone in concrete cells with broken bones and recent surgeries, their pain medication deeply inadequate.

In the coming days, the agency is expected to announce significant changes related to the health of migrants, including policies requiring Border Patrol agents to conduct more thorough interviews of each migrant who is processed through the system, and to refer all those who need care to a medical provider.

The agency is also building a large new processing center in El Paso and adding $47 million to a private contract for migrant medical care.

“We’re doing everything we can to ensure rapid medical care when needed,” Homeland Security Secretary Kirstjen Nielsen said at the White House in January. “The men and women of CBP and ICE are doing the best they can with what they have, but they don’t have the facilities, the resources or the legal authorities to keep up with this crisis.”

Rep. Raul Ruiz, D-Calif., who is also a physician, helped secure funding for additional measures to improve migrant health after visiting border facilities where he said he saw children coughing and sneezing and infants without diapers, all packed tightly into cells with little in the way of food, soap and other basics. The Border Patrol stations and those working there were “unprepared, untrained and underequipped in dealing with the humanitarian needs of families,” he said.

The moves come after years of warnings from both inside and outside government that were largely ignored by an agency that saw its primary mission as law enforcement — catching and deporting illegal border crossers, not nursing them back to health.

“Border Patrol is a law enforcement agency. It’s not a humanitarian agency,” said Dr. Alexander L. Eastman, a senior medical officer with the Homeland Security Department who is trying to put into place, for the first time, a comprehensive approach to the care of migrants across the department.

Some health care workers said they have seen Border Patrol agents in the field prioritize enforcement of immigration laws over migrants’ urgent medical needs. Ambulance crews near the border say they sometimes face delays at Border Patrol checkpoints.

In one case around five years ago, described to The Times by two people who worked for an emergency medical response team in Starr County, Texas, a critically ill woman was driven across the bridge from Mexico into Rio Grande City and loaded into an ambulance from a nearby hospital. A paramedic, Sergio Garza Jr., began to help her with her breathing. But a CBP employee, he said, opened the back doors of the vehicle and ordered the patient sent back, because she did not have papers to enter the United States.

Garza and the director of his ambulance company protested, to no avail. Garza grudgingly transferred the patient back to a Mexican ambulance, which did not have trained personnel aboard, both he and the director recalled. Garza said he showed the patient’s husband how to squeeze an oxygen bag to try to keep his wife alive as she was driven toward a distant Mexican hospital. She died on the way there, the emergency workers said.

Persistent Problems

For at least a decade, families and advocacy organizations have reported lapses in medical care for people in the custody of CBP. Complaints filed over the past few years included a mother who gave birth prematurely and was forced to stay with the baby in a “dirty hold room,” a detainee who was refused access to prescribed heart medication, and a woman who had heavy vaginal bleeding after a sexual assault and was not provided any medical attention.

The number of deaths remains unknown and is perhaps unknowable — the agency until December was not required to independently review or publicly report health-related deaths in its custody. And the consequences of failing to address urgent medical needs often emerge after detainees are quickly passed on to another agency, or released.

In 2015, CBP addressed some of the criticisms by establishing its first nationwide standards on transport and detention. However, the standards are nonbinding — the agency cannot be sued for not following them — and the subject of medical care in detention covers less than a page.

Detention is intended to be brief — 72 hours or less, according to the standards. However that guideline is often broken. Felipe Gómez Alonzo, the boy who died in December and had influenza, was in his sixth day of detention when he was taken to a hospital, according to a timeline provided by the agency.

At the hospital, Felipe was found to have a 103-degree fever. He was discharged from the emergency room several hours later, and agents took him back to a temporary holding cell at a highway checkpoint. Hours later, as the boy grew sicker, no medically trained agents were on duty there. He was returned to the hospital, but lost consciousness on the way.

“Children should not be held in CBP holding cells longer than 24 hours,” said Kathryn Hampton, a program officer for Physicians for Human Rights and the author of a recent study that found that the focus on securing the border has come at the cost of migrants’ safety.

In some cases, Border Patrol agents take sick migrants to be seen at hospitals, but problems persist once they are brought back to CBP’s crowded, ill-equipped facilities.

Sonia Diaz-Castro, 39, an asylum-seeker from Honduras, had fallen off the top of a 25-foot border wall as she entered the United States last year and was left barely able to move, with a broken elbow and pelvis.

Border Patrol agents in New Mexico took her twice to local hospitals, and a doctor at one of them said he was promised by the agents that she would be given a wheelchair and have someone on hand to help her get around. She had neither. Though she was barely able to move, she was left alone in a concrete cell. When she had to use the toilet, she was forced to drag herself across the floor using her broken arm.

“I just felt like crying out — like the only thing I could do was cry, and when I think about it, it still makes me want to cry,” Diaz-Castro said of the experience.

The Journey Through Custody

On a typical afternoon in early February, Border Patrol radios in South Texas crackled with reports of “bodies,” people whose unauthorized crossing of the border had been detected by ground motion sensors and cameras on poles and tethered radar blimps.

Agents responded as about 60 people from Honduras, Guatemala, Ecuador and Nicaragua, including mothers with children and some unaccompanied minors, clambered off rafts after crossing the Rio Grande. Hefting bags and babies, they climbed a muddy dirt path that cut through spiny brushlands, walking toward the agents, who awaited them at a gap in the border wall.

Rene Reyes, a Border Patrol agent and emergency medical technician, eyeballed them for, he said, “anything life-threatening.”

Reyes stopped briefly to ask parents about a boy with surgical scars on his head who was wearing a mask over his nose and mouth. He had a condition that causes too much fluid to build up in the brain, but he appeared stable. “The kids look OK,” Reyes concluded. His initial assessment of the entire group lasted less than five minutes.

The children would get a more thorough medical check at their next stop, one of two temporary detention facilities in an industrial part of McAllen. Inside the agency’s largest processing center for migrants, chain-link fencing divides a vast warehouse with concrete floors into clusters of cells separating men from women and older children from parents. The site was opened in 2014 specifically for the temporary holding of families and unaccompanied children. When that site is full, an older facility with enclosed, jaillike cells processes families several blocks away.

That afternoon, medical screeners sent a newly arrived 6-month-old, Victoria Medina, to the hospital after noticing that she was sick with a fever, severe cough and diarrhea. Hospital workers treated the baby and sent her back to CBP.

That night Victoria’s mother, Mayte Medina, an 18-year-old from Honduras, lay on the bare floor of her chilly isolation cell under a thin Mylar sheet and held on tight to her coughing baby. The fever broke, but the diarrhea continued; the bottle of medicine Medina had carried with her to treat it had been in her backpack, which was confiscated when she was taken into custody. “I told everyone about it, everyone that saw her,” Medina said. “They never gave her anything.”

Medina’s relatively easy access to medical care was possible in part because she was apprehended in the heart of the Rio Grande Valley, the most heavily trafficked way station for migrants in the United States. Last year, more than 63,200 migrants traveling as families were apprehended there.

The Border Patrol facilities in McAllen are among the few in the country that have a small number of midlevel health professionals — nurse practitioners or physician assistants — on site. As government officials examine how they might expand medical services, those sites have been looked at as potential models.

But even in those places, providing care in a facility where the ultimate decisions are controlled by law enforcement authorities sometimes frustrates practice and strains ethics. A former contract health care worker at the McAllen sites, who was not authorized to speak on the record by her previous employer, Loyal Source, recalled several occasions when she had alerted agents that a patient needed to go to the emergency room. Two or three hours later, she said, the patient was still there.

Sometimes, she said, she blocked migrants with high fevers from being released to longer-term detention facilities. But she also sometimes felt intimidated, as if she would be blamed for slowing down the flow.

She said that according to protocol, if a woman claimed that she had been raped, she had to be offered access to medical care to check for pregnancy, trauma and sexually transmitted infections. But that didn’t always occur, she said.

Dangerous Terrain

In recent months, large groups of children and families have crossed into the United States in remote desert areas lacking in medical infrastructure, including Antelope Wells, New Mexico, where one of the fatally ill children, Jakelin Caal Maquin, had arrived. A total of 15 Border Patrol stations or ports of entry that are within 100 miles of the southern border have no hospital within an hour’s drive, the Times review found.

It is a perilous twist on a problem that has existed for years, after changes in border enforcement practices pushed furtive crossings into these areas.

Some migrants encounter agents and turn themselves in; others spend days traversing vast ranchlands in extreme heat. Hundreds die every year. Agents often have to extract sick migrants from rough terrain to meet ambulance personnel, who may have to drive for hours to reach hospitals.

An earlier attempt to solve the problem led to the creation in 1998 of a unit trained in tactical rescues and emergency medical services that has performed thousands of medical interventions. A separate program trains regular agents as emergency medical technicians. Overall, around 6 percent of Border Patrol agents can act as emergency medical services providers. Still, the vast majority have only basic training. Their protocols and equipment are limited. And they are not present everywhere their skills are needed.

Where local emergency rooms are close at hand, Border Patrol agents tend to err on the side of caution, taking their charges for costly and sometimes unnecessary medical evaluations, several health providers said.

In other cases, the Border Patrol focuses on moving migrants quickly through the system, and many end up in shelters and clinics run by charities, such as the one operated by Catholic Charities in McAllen.

On a recent evening, dozens of migrants were dropped off at a shelter near the southern border of California, run by the San Diego Rapid Response Network. They stood outside, lined up near white tents under lights powered by a roaring generator. Medical workers screened them for communicable diseases and other conditions.

The rotating medical team diagnosed many untreated conditions that could spread, including 362 cases of lice, 113 cases of scabies, 22 cases of possible influenza, and four cases of chickenpox in the first two months of this year. The medical professionals referred 52 people to an emergency room.

One young man stood out that evening. He limped to the tent on crutches, in great pain. A metal fixator emerged from his lower left leg, swaddled in layers of bloodied gauze. The only medical record a nurse could find in his belongings was a single X-ray showing a severe fracture he had suffered on his journey to the United States.

The man had undergone surgery on his leg at a nearby hospital and was returned to detention the previous night. Now he was at the shelter. “They just dropped him here,” Dr. Kathy Fischer, the doctor on duty, said with a note of incredulity in her voice. “It’s kind of crazy.”

This article originally appeared in The New York Times.