(CNN) A 10-year-old migrant child died while in the care of the Department of Health and Human Services' Office of Refugee Resettlement in September of last year, according to department spokesman Mark Weber.

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 US and being apprehended by federal authorities. Her death predates the five children known to have died.

In a statement, Weber said 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 in Omaha, Nebraska, where she died due to fever and respiratory distress on September 29, according to Weber.

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."

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