To figure this out, researchers dug into health insurance claims data to see what kinds of diagnoses patients were prescribed antibiotics for. Some illnesses—like streptococcal tonsillitis, bacterial pneumonia, or lung abscesses—they determined would pretty much always require an antibiotic prescription. Other ailments don’t always merit them, though. Inflamed sinuses, emphysema, and lower respiratory tract infections are just a few of those deemed to only sometimes require antibiotics. Finally, there was the never category—those diagnoses that shouldn’t ever be associated with an antibiotic prescription. Upper respiratory tract infections, asthma, and allergic rhinitis (inflamed nasal lining) were all in this last group. They note in the study that they erred on the side of assuming a prescription might be necessary such that their estimate would be conservative.