Tamiflu (oseltamivir) work for all strains of the flu? Do I need a PCR genetic study?

Unclear question. Do you mean that you need to do pcr genetic study on the strain of flu that may be affecting you? Tamiflu (oseltamivir) should be taken within the first couple of days of infection for it to be effective. If you wait for pcr results, you would have missed the appropriate time for treatment.