Quest Diagnostics Inc. said that one of the billing collections firms it works with experienced a data breach on its web payment system that may have affected 11.9 million patients, the Wall Street Journal reported. The data breach may have involved the collection of patients’ financial information, such as credit-card numbers and bank-account information, as well as medical information and personal details, the company said Monday. The billing collections vendor, American Medical Collection Agency, notified the company of the breach on May 14, the company said. Quest outsourced its billing operations to health-care revenue manager Optum360 LLC, which contracted AMCA. Quest said laboratory results weren’t given to AMCA and therefore weren’t affected by the breach.