When do covered entities need to report ransomware incidents to HHS?

At the PHI Protection Network conference last week, we spent a lot of time discussing the increasing rate of ransomware attacks. I asked a number of people whether they thought that ransomware attacks that (merely) locked up the data with no evidence of exfiltration had to be reported to HHS.  I got a variety of answers, so I put some hypothetical scenarios to HHS and asked them to clarify. Lesley Cothran, a Public Affairs Specialist, answered for the department:

Under HIPAA, an impermissible use or disclosure of protected health information is presumed to be a breach (and therefore, notification is required) unless the entity demonstrates that there is a low probability that the protected health information has been compromised based on a risk assessment of at least the following factors:

1. The nature and extent of the protected health information involved, including the types of identifiers and the likelihood of re-identification;

2. The unauthorized person who used the protected health information or to whom the disclosure was made;

3. Whether the protected health information was actually acquired or viewed; and

4. The extent to which the risk to the protected health information has been mitigated.

Because it is considered to be a “disclosure” if access has been provided (without regard to whether or not the information actually was accessed or viewed), and hackers using ransomware do have access to the data, an impermissible disclosure has occurred – and notification is presumably required – unless a “low probability of compromise” has been demonstrated, and “whether the [PHI] was actually acquired or viewed” is only one of the
factors.

So… how would you demonstrate a “low probability of compromise” in a ransomware attack? If you can demonstrate by logs that no data were exfiltrated and you can figure out what happened once the attackers got in, and if you have a full backup of patient data so that you can restore from backup after removing malware and you feel confident that no patient data has been corrupted or altered, would you feel that you had adequately demonstrated low risk and that notification was not required?  Or do you think more is required to justify no need for notification?