Hansen was injected with an antidote after having been infected by an Exocel. A parasite the size of the Exocel would require much more than an injection to deal with.
In gameplay and in-engine cutscenes, Tom Hansen carries a two-toned M1911 A1 that fires .45 ACP rounds. In full-motion CGI cutscenes, he carries a black Beretta M92 FS that would fire 9mm rounds.
The United States Coast Guard is referred to as the 'Coast Guards' on a poster.
The Russian mercenaries are using American pistols, which they are unlikely to be using.
Just before Hansen finds Ms. Kamsky, she is heard talking to someone. When he reaches her, no one can be found.
Hansen was told that Ms. Kamsky was important and was told not to lose sight of her. Later he is told by the same man to forget about her after she disappears.