OMAHA, Neb. -- U.S. authorities say a 10-year-old girl from El Salvador died in Omaha last year after being detained by border authorities in a previously unreported case.
The death marks the sixth known case in the last year.
The girl, whose death was not reported publicly for nearly eight months, is now the sixth migrant child known to have recently died after journeying to the U.S. and being apprehended by federal authorities. Her death predates the five children known to have died.
The U.S. Department of Health and Human Services said Wednesday that she died Sept. 29 at Children's Hospital in Omaha of fever and respiratory distress.
Spokesman Mark Weber said the department began caring for the unidentified girl in March 2018. Weber said the girl was "medically fragile," with a history of congenital heart defects.
In a statement, Weber told CNN that the 10-year-old girl entered the office's care in San Antonio in March 2018. She had a history of congenital heart defects.
He said the child had surgery complications that left her in a comatose state. She was transported to a nursing facility in Phoenix and later transported to Children's Hospital, where she died.
He did not say when she entered the U.S. or whether a parent or adult accompanied her. HHS provides care to children the government considers unaccompanied.
When asked by CNN why HHS did not announce the death of the 10-year-old girl at the time, Weber said they had prepared a statement at the time of her death but reporting requirements include notifying "appropriate officials" and "media is not part of the list."
The deaths of immigrant children in U.S. government custody have sparked calls for investigations and changes to Trump administration policy. Weber said the department was committed to protecting the children in its custody.
CBS first reported the child's death.
Since December, five children are known to have died after arriving at the US border from Guatemala. Two young children died weeks apart in December in government custody, spurring congressional hearings on the matter.
CNN contributed to this article.