Thanks for the feed back,
In the example you gave, with HIV and Hep C..really, either one could result in a POS test before the other, but most likely the HIV would show up on a test first. IF you are talking about becoming infected with both viruses as a result of ONE encounter/exposure.
The term "co-infection" doesn't mean that two illnesses/viruses were transmitted at the same time...it simply means, that a person is "co-infected" with more than one organism at the same time...ie HIV and Hep B for example. It certainly doesn't mean that the person became infected at the same time...it just means that they test POS for both viruses. One could have been "caught" 10 years prior to the other, but once there are two diseases, it is a "co-infection".
As to which one would test POS first...it would depend on which one was transmitted first. In the rare instances that someone DID transmit two viruses (like HIV and Hep B) as a result of ONE single encounter....either test could become pos first. The answer to that question TOTALLY depends on what two diseases you are speaking of....the example I gave are two very similar viruses, in transmission and in seroconversion...therefore either one could produce antibodies first. If if was a different virus, it would depend on the infectious period and typical seroconversion times.