Oh good grief. Here is the last sentence from the first paragraph of that article.
"Most of the time" means that more than half of all adverse events are never disclosed. The author fails to provide any objectively verifiable support whatsoever for such an asinine comment. That's because it's demonstrably false.
As a condition of participation, Medicare requires healthcare providers to report adverse events like surgical infections, healthcare-acquired infections, and death.
It's all publicly available information. Providers' payments from Medicare, Medicaid, and managed care payers like Aetna, Blue Cross, Cigna, United, etc. are all impacted by patient safety processes and outcomes that are reflected in claims data and medical records. Providers also voluntarily report patient safety information to dozens of other organizations like the Department of Health and Human Services, Joint Commission, Centers for Disease Control, Federal Drug Administration, Agency for Healthcare Quality and Research, National Committee for Quality Assurance, etc.