The New Mexico Office of the Medical Examiner released its autopsy findings for Felipe Gomez Alonzo on Wednesday, two days after Guatemalan authorities said they had received a copy of the report disclosing the boy had a rapid, progressive infection that led to organ failure.
An autopsy released last week for 7-year-old Jakelin Caal Maquin, the other Guatemalan child who died, showed she too had a bacterial infection that quickly led to sepsis and organ failure.
Their deaths, just over two weeks apart, came amid a rise in the number of families arriving at the United States' southern border.
Homeland Security Secretary Kirstjen Nielsen has taken to social media in recent days, tweeting that Congress must confront what she called an emergency by giving border and immigration authorities the tools and resources needed to "fulfill our humanitarian and security mission."
She visited El Paso, Texas, on Wednesday, marking her first stop on a border tour aimed at assessing the surge of migrants and the department's response. "Our system and facilities were never structured to withstand the current influx of immigrants," she said.
Gomez Alonzo and his father, Agustin Gomez, were apprehended by the Border Patrol in mid-December after the family said the two left Guatemala because of the extreme poverty and lack of opportunity they were facing.
The father said others from his community had been able to cross the U.S. border with children, and he figured he and his son would have the same luck. Felipe was chosen to go with his father because he was the oldest son.
Once in Border Patrol's custody, Gomez Alonzo and his father were taken to several facilities including the processing center at the Paso del Norte port of entry, then the El Paso Border Patrol station.
The day before Gomez Alonzo died, they arrived at about 1 a.m. at the Border Patrol station in Alamogordo, New Mexico, about 90 miles (or 145 kilometers) north of the border, according to the agency. Officials said the two were moved there "because of capacity levels" in El Paso.
The day Felipe died, a border agent noticed the boy was coughing and had "glossy eyes," and sent him to the hospital, Border Patrol said.
He was found to have a 103-degree fever (39.4 degrees Celsius), officials have said.
New Mexico medical examiners said in their report that the boy complained of a sore throat, congestion and fever before being taken to the hospital, where he tested positive for flu.
He was held for observation for 90 minutes, federal authorities said, before being released with prescriptions for amoxicillin and ibuprofen. But the boy fell sick hours later and was readmitted to the hospital, where he later died.
The boy reportedly had become unresponsive on the way to the back to the hospital, medical examiners said.
"Our thoughts are with his family during this difficult time," Dr. Kurt Nolte, the state's chief medical investigator, said in a statement.
New Mexico authorities previously said the boy tested positive for the flu.
His autopsy showed he suffered a staph infection in his lungs before the bacteria entered his bloodstream and sepsis set in. A toxicology report released by the medical examiner shows he had Benadryl in his system.
Jakelin Caal died Dec. 8 in El Paso, just over a day after she was apprehended by Border Patrol agents with her father after entering the U.S.