How did Piggy infection start?

How did Piggy infection start? Due to his signature, this has been confirmed to be written by Mr. P. This suggests that one of his direct family members (wife) is sick, and he is trying to find a cure. He then uses Substance 128 on the Piggy family which inevitably and unexpectedly turns them infected by The Virus.

Due to his signature, this has been confirmed to be written by Mr. P. This suggests that one of his direct family members (wife) is sick, and he is trying to find a cure. He then uses Substance 128 on the Piggy family which inevitably and unexpectedly turns them infected by The Virus.