1) Infection 
A superinfection is generally defined as a second infection superimposed on an earlier one, especially by a different microbial agent of exogenous or endogenous origin, that is resistant to the treatment used against the first infection. An example of this in bacteriology is the overgrowth of endogenous Clostridium difficile which occurs following...
Attempt to infect a host with a second virus, usually a different strain of the first infecting virus. 
a new infection complicating the course of antimicrobial therapy of an existing infectious process, and resulting from invasion by bacteria or fungi resistant to the drug(s) in use. It may occur at the site of the original infection or at a remote site.
<microbiology> A new infection complicating the course of antimicrobial therapy of an existing infectious process and resulting from invasion by bacteria or fungi resistant to the drug in use. ... It may occur at the site of the original infection or at a remote site. ... (18 Nov 1997) ... 
(soo″pәr-in-fek´shәn) a new infection occurring in a patient having a preexisting infection; for example, bacterial infection may occur in patients with viral respiratory disease, or a chronic hepatitis B carrier may become infected with hepatitis D virus. Superinfection can complicate the course...
the acquisition of a second infection while a previous infection is still present.
Type: Term Pronunciation: sū′pĕr-in-fek′shŭn Definitions: 1. A new infection in addition to one already present.
[n] - infection that occurs while you are being treated for another infection
secondary infection that may develop as a result of long-term, broad-spectrum antimicrobial use
noun infection that occurs while you are being treated for another infection
marked proliferation of a parasitic microorganism during antimicrobial treatment for another infection.