Anti-matter copies were created of everyone who traveled through the Einstein-Rosen bridge during the incident where Lockdown turned the bridge into Anti-matter. The anti-matter copies differed in certain very subtle ways (for example Oscar Shelton was right-handed whereas Rudyard Shelton was left-handed. There were also copies made of all their equipment, with similar slight changes (the radios only worked when the call button was not pressed).
A later copy was made of Seska, implying that the bridge was permanently tainted with this downside. However it was never used again after this. (Card of Ten) The bridge left behind on Earth was used eight months later without this side effect, indicating that only the anti-matter bridge that went with the away team was infected. (Pavlov's Checkmate)