Sometimes an analysis of the effluvium from a sinus washing can tell what kind of pathogen (if any) is the cause of the trouble, but not always. Doctors at Mayo Clinic did a study and found that fungal sinusitis was way more common that previously thought, but they looked at actual tissue samples taken during sinus surgery (adnoid removal, etc.) instead of just the sinus washings.
Alternative practitioners can sometimes use applied kinesiology (muscle testing) to determine which type of infection a person has. This method is about 70-80% accurate if the practitioner is experienced.
Another method for determining the pathogen type is a trial of medication - antifungal for a bit, then if symptoms don't clear, move on to antibiotics, etc.
In any case, it would be good to discuss options with your doctor to see what he says and if he thinks one or another may be more likely (he may have gotten clues from details discussed during your appointment, etc.). Or he may have another idea for how to determine what type of pathogen is the culprit.
I hope this helps - take care,
Gluten & Sulfite Sensitivity, Many Food/Inhalant/Medication Allergies & Intolerances, Asthma, Gut issues (dysmotility, non-specific inflammation), UCTD (Lupus?), Osteoporosis, Anemia, T- & B-Cell Lymphopenia, malabsorption/malnutrition, Lyme Disease (Igenex Lab IgM WesternBlot positive/CDC negative), etc.
Meds: Pulmicort, Injectable Vitamin B12, Herbs, Nutritional Supplements, Homeopathy.