HOUSTON  — A Mexico City toddler who traveled to the Texas with family to visit relatives is the first confirmed death in the U.S. from swine flu.

The boy, who was nearly 2 years old, arrived in border city of Brownsville with “underlying health issues” on April 4 and developed flu symptoms four days later, the Texas Department of State Health Services said. He was taken to a Brownsville hospital April 13 and transferred to the following day to a hospital in Houston, where he died Monday night.

The cause of death was pneumonia caused by the flu virus, Cameron County Judge Carlos Cascos said.

Officials did not specify what underlying health issues the boy had before arriving in the U.S.

State health officials declined to identify the boy or his family, citing privacy concerns, medical confidentiality and “the absence of an obvious health threat from the boy to the public at large.”

State health officials said the boy would not have been infectious when he flew from Mexico City to Matamoras, across the border from Brownsville. None of his close contacts have developed symptoms.

Health officials in Brownsville are trying to trace his family’s trip to find out how long they were in the area, who they visited and how many people were in the group, Cascos said.

The boy’s family members “are healthy and well,” Houston’s health director, Dr. David Persse, said at a Wednesday news conference.

The toddler was about 2 years old. Houston officials said he was 23 months old, but state officials said he was 22 months old and could not immediately explain the discrepancy.

The Centers For Disease Control and Prevention confirmed the death earlier Wednesday.

Swine flu is suspected of killing more than 150 people in Mexico and sickening over 2,400 there.