Health-care hack spreads pain across hospitals and doctors nationwide

The fallout from the hack of a little-known but pivotal health-care company is inflicting pain on hospitals, doctor offices, pharmacies and millions of patients across the nation, with government and industry officials calling it one of the most serious attacks on the health-care system in U.S. history.

The Feb. 21 cyberattack on Change Healthcare, owned by UnitedHealth Group, has cut off many health-care organizations from the systems they rely on to transmit patients’ health-care claims and get paid. The ensuing outage doesn’t appear to affect any of the systems that provide direct,...