My yard is full of mosquitoes; how do I know which ones have EEE?

There is no way of telling which mosquitoes carry EEE without testing them. Currently, the mosquito-borne viruses to be most concerned with are EEE and West Nile Virus (WNV).  The precautions for both are the same – wear long sleeved shirts and long pants when out during high mosquito activity, and use an appropriate insect repellent.