How can you tell the diffrence between strep and a virus?

Throat swab: Generally speaking, it can be difficult to tell. On exam, strep causes purulent secretions and viral infections do not with exception of mono. Generally a throat swab can be pretty reliable. But a good physical exam is usually all that is needed to determine the difference between a bacterial vs. Viral throat inefection.

Some basics: Most sore throats are viral but symptoms plus a positive quick test/culture will find the strep A that needs antibiotics. People can carry strep A but not get sick from it (carriers) & these range from 5-20% of the population on a seasonal basis. These carriers often expose/infect susceptible people. Symptoms do overlap & physicians rarely depend on exam alone unless you have a scarlatina rash.