Blue Cross and Blue Shield of Illinois has signed accountable care organization agreements with four providers and now has nine ACO contracts in the Land of Lincoln, the insurer recently announced. Reflecting the growing trend of provider consolidation, merger and acquisition, the insurer's new ACO partners are part of some of the nation's largest health systems. The Alexian Brothers Health System, for example, is part of Ascension (the nation's largest nonprofit system) and in the midst of signing a joint operation agreement with Adventist Midwest Health, a division of Adventist Health System (the nation's largest faith-based system). Announcement