system
Given the following post, respond as if you're commenting on Reddit:
human
What are the challenges in developing a rapid screening test to determine whether an infection is bacterial vs viral?

It seems like one of the main problem is that there are tons of bacteria and viruses always present that aren't causing an infection. Could we use the quantity of a given bacteria in the location of an infection (e.g. sputum for a throat infection) since there would presumably be more of the infectious bacteria there? Are there any technologies or analytical techniques on the horizon which might help?
gpt
It's actually not that big of a problem. Viral and bacterial infections are not that similar in many aspects so you often know just by the symptoms. 

For the ones where you don't know there are several things you can do :

Measure CRP levels : In respiratory infections it's sometimes hard to differentiate between viral and bacterial. Bacterial infections typically have CRP levels >100 while viral are lower. If CRP is <50 you pretty much know it's viral if it's >100 it's bacterial.

Do PCR or antibody search tests : In other infections there are not many viruses that come into question so you just test directly for them. Like if you have Pneumonia and a viral one is a possibility it's probably going to be Influenza, Parainfluenza or Adenoviruses (rarely Herpes). 


Also if you find a bacterial or viral colonisation and the patients shows symptoms that fit, it's nearly always going to be an infection by said agent., even if it's possible to be colonized without being sick.