"Tip of the iceberg"

According to this NZ Herald report;

In the 12 months to July, Starship - New Zealand's largest paediatric hospital - admitted 48 children who were victims of "suspected or definite" child abuse.

Most cases involved children under a year old. Seven of those children did not survive, a figure Starship said was unusually high compared with previous years.

Overall, this equated to almost one hospital admission a week - with many of the cases "as horrific as the Kahuis", said Patrick Kelly, clinical director of the hospital's child abuse team.

The writer refers to the Kahui abuse as "just the tip of the iceberg" but it could just as easily be the 48 cases are the tip of the iceberg. For instance, how many admissions occur at other hospitals?