Low number suppression can stop identification, but even in higher numbers it can be possible to identify someone. If we asked two questions:
(Q1): How many individuals are there that had a result in October that was positive.
(Answer): 400
(Q2): How many individuals are there that had a result in October that was positive and was Male.
(Answer): 399
From these two questions, it would be possible to establish that there was likely to be one person that had a result in October that was positive and was Female. Therefore, we have by-passed the low number suppression applied.
To protect against someone asking multiple questions and subtracting counts to identify someone, each Data Partner can enable rounding on results, which ensures they are never exact results but sufficiently precise to allow the researcher to know the scale of the dataset.