The New Mexico Office of the Medical Investigator said Thursday that an 8-year-old boy who died in U.S. custody on Christmas Eve tested positive for influenza B.

The medical investigator's office cautioned in a statement that the cause of death for Felipe Gómez Alonzo, who died minutes before midnight on Dec. 24, was still under investigation, but it was determined that he had been suffering from the flu.

"Results of nasal and lung swabs have tested positive for influenza B," the office said. "While this result indicates that the child had influenza, determining an accurate cause of death requires further evaluation of other laboratory specimens and interpreting the findings in the context of the symptoms and autopsy findings."

The announcement came as pediatricians were raising questions about the medical care given to Felipe, who was apprehended at the border Dec. 18 with his father.

Felipe was taken to a New Mexico hospital Monday after he was coughing and "appeared to have glossy eyes," according to a statement from CBP. The boy was originally diagnosed with a cold but was found to have a 103-degree fever and was kept for observation for an additional 90 minutes before being released and transferred to a highway checkpoint with his father Monday afternoon, according to the CBP statement.

By that evening, Felipe was vomiting, nauseous and lethargic and lost consciousness during transport back to the same hospital, according to the statement. He was pronounced dead at 11:48 p.m.

Dr. Colleen Kraft, president of the American Academy of Pediatrics, said that while a cause of death has yet to be determined and many details are unknown, Felipe’s death highlighted the need for pediatric-trained personnel at CBP facilities.

“This child wasn’t appreciated to be as ill as he was,” she said.

Kraft added that while she was not faulting the hospital, “clearly his treatment wasn’t adequate.”

Felipe Gómez Alonzo on Dec. 12, 2018 near his half-sister's home in Yalambojoch, Guatemala. Catarina Gomez / via AP

She added that CBP having pediatricians or trained staff could have impacted the boy’s treatment.

“What I can tell you is that somebody who had pediatric experience and evaluated this child would really have looked at what happened when he went to the hospital, should this child have stayed in the hospital? What were his vital signs? Did this child have influenza?” she said.

Kraft said CBP Commissioner Kevin McAleenan had called her this week.

"He recognizes that this is a problem," she said. "He was willing to start the conversation, we don't have any details beyond that."

Felipe is the second child to die in migrant custody this month after 7-year-old Jakelin Caal Maquin, also of Guatemala, died in Border Patrol custody on Dec. 8.

Kraft said both deaths show “our border processing facilities are no place for children.”

Both Felipe and Jakelin's death have led to calls for congressional investigations. House Democrats on Thursday released a statement calling for all evidence related to the deaths be preserved and said they would conduct hearings and oversight into the deaths and conditions in the CBP's facilities.

Dr. Alan Shapiro, medical director and co-founder of Terra Firma, an organization that provides medical and legal services for migrant children, said such facilities have been found to have very cursory medical services, “so it’s very easy for illnesses to get missed.”

He said while details were still unknown, Felipe’s death raises two issues.

“There’s the issue of the care that the child received at that hospital, and I really cannot comment on that except to say that the other part of the equation is that this is a child that was living in the U.S. immigration detention system,” he said.

“The system is not designed to take care of children, and it’s not designed to be able to monitor a rapidly deteriorating child,” he added.

Shapiro said CBP facilities and detention centers run by Immigration and Customs Enforcement often hold many migrants at once, “a recipe for the spread of infectious diseases.”

Felipe Gomez Alonzo's mother, Catarina Alonzo, at her home Thursday in the village of Yalambojoch, Guatemala. Luis Echeverria / Reuters

A Department of Homeland Security official said Thursday that Secretary Kirstjen Nielsen would be traveling to El Paso and Yuma on Friday and Saturday. Nielsen previously said in a statement that she would be headed to the border “to see first-hand the medical screenings and conditions at Border Patrol stations.”

She added that she had asked the Coast Guard Medical Corps to assess CBP’s medical programs and the Department of Defense “to provide additional medical professionals.”

All children in CBP custody would receive “a more thorough hands on assessment at the earliest possible time post apprehension — whether or not the accompanying adult has asked for one,” she said.

John Kahler, a pediatrician and cofounder of MedGlobal, a nonprofit working to address health needs around the world, said that based on Felipe’s symptoms as detailed by CBP’s statement he believed the hospital should have checked for influenza and done a chest x-ray, which could have picked up whether the child had pneumonia or other potentially deadly issues in his lungs.

“If there wasn’t a chest x-ray in that story, that’s really questionable care,” he said.

He added that medical staff trained to care for children at immigration facilities could more quickly and effectively detect signs that a child was very ill.

Some processing facilities do not have medical personnel on duty at all times or EMT-trained agents present. CBP did not immediately respond to questions on what those additional medical checks would look like or if any medical personnel or EMT-trained agents were present at any of the facilities Felipe and his father were held at.

Kahler said children often exhibited more subtle symptoms that a pediatric-trained professional could better assess over an EMT-trained border agent.

“Really, whoever is doing initial screenings for these children, it’s going to be quick," he said. "Pediatricians can do that much better than EMT-trained agents.”