From their website (they also published a press release on this incident):
Shields Health Solutions takes seriously the confidentiality and security of patient information. Regrettably, this notice is to inform patients of a recent incident that may have involved some patients’ information.
Shields provides specialty pharmacy services to hospitals and other covered entities. On October 24, 2019, Shields learned of suspicious activity related to an employee’s email account. We immediately took steps to secure the account and worked with a cybersecurity firm to assist with our investigation. The investigation determined that an unauthorized person gained access to a single employee email account between October 22, 2019 and October 24, 2019. However, our investigation determined that the account contained some patient records, including names, dates of birth, medical record numbers, provider names, prescription information, clinical information, insurer names, and limited claims information. The information did not include patient Social Security numbers or financial account information.
We have no indication that any patient’s information has been accessed or misused. However, in an abundance of caution, we began mailing letters to affected patients on December 16, 2019 and established a dedicated call center to answer questions that patients may have. If you believe you are affected and do not receive a letter by March 2, 2020, please call 844-967-1230 from Monday through Friday between the hours of 9:00 a.m. and 6:30 p.m. Eastern Time. We recommend affected patients review the statements they receive from their health care providers. If they see services they did not receive, patients should contact the provider immediately.
We sincerely regret any concern or inconvenience this incident may cause. To help prevent something like this from happening in the future, we are taking steps to further enhance the organization’s data security procedures, including implementing multi-factor authentication on employee email accounts.
They do not mention how many patients were notified nor which hospitals or covered entities had patients affected by this incident, but their website shows a number of Massachusetts and Connecticut covered entities that they have relationships with so it may be any or some of them.