The infectious agent most often complicating influenza is Streptococcus pneumoniae. In a superinfection model, pneumococcal pneumonia after influenza virus infection was established in six-week old mice using sublethal doses of both microbes (Hayashi et al., 2006). S. pneumoniae was inoculated intranasally 7 days after exposure to influenza virus and death in the presence of both agents only began at day 4 post bacterial exposure. The efficacy of several quinolones against bacteria-induced pneumonia in this model was evaluated, with gatifloxacin used successfully to treat the pneumococcal infection.