Healthcare providers are obliged to keep your medical data confidential. They may only share it with other healthcare providers that are directly involved in your treatment. You may however object to this exchange.
Providers may only share your data with third parties after your approval. Medical data of children under 16 may be shared with their parents unless this conflicts with good care.
Only in some limited cases health insurance providers may request information to verify that a healthcare provider or healthcare institution has provided the care for which the health insurer pays (= legality check) or to verify that the care or treatment given was the best choice for the patient (= effectiveness control).