Wow!! I think you are starting to sort this out.
A question though, because it was not clear from your comments. Is the model:
1. Widespread streptococcus suis and widespread Avian Flu that just happen to both be present in many animals. The strep suis is aysmptomatic and the symtoms are entirely due to Avian Flu. However, when the animals are tested, they test positive for the strep suis, so it is assumed that that is the causal factor.
-or-
1. Widespread streptococcus suis and widespread Avian Flu that just happen to both be present in many animals. Normally the strep suis is asymptomatic but in the case of a dual infection with Avian Flu, the immune response is suppresed by the Avian Flu and you have the symptoms from both.
The first model is definitely possible, maybe even probable.
The second model--I think that Avian Flu causes a vigorous immune response, and in the case of those victims who develop cytokine storm, a deadly vigorous immune response.
Incidently, for those reading here I want to point out that there is solid research showing that Haldol (yes, the major tranquilizer antipsychotic HALDOL) is useful in treating cytokine storm, more so than prednisone or other steroids. Google can point to many articles about this.
Please please please put that info about Haldol in the back of your mind. You never know if it might be useful, especially if someone you love has that kind of response to the flu. Cytokine storm can kill. Haldol may help treat it.