All those big health-care mergers may mean financial risk is getting concentrated By: MarketWatch October 29, 2018 at 13:44 PM EDT Just ten companies account for half of the investment-grade health care bonds outstanding, a new report found. Read More >> Related Stocks: Aetna Allergan Plc CVS Health Corp Cigna Corp Express Scripts Holding HEALTHCARE Mylan Teva Pharmaceutical Industries ADR