Certain types of antibiotics can be used to treat some parasitic infections. Flagyll is one example of this - it is a particular type of antibiotic that happens to have anti-parasitic activity. And in the natural healing world, many of the anti-parasitic herbs also have anti-bacterial properties...clove oil is a good example of this.
Another reason is that they don't know what else to throw at this bug, and since many people have improved with antibiotic treatment, that's what is prescribed...
Chronic Lyme Disease, Gluten & Sulfite Sensitivity, Many Food/Inhalant/Medication/Chemical Allergies & Intolerances, Asthma, Gut issues (dysmotility, non-specific inflammation), UCTD ("Secondary Lupus-Like Syndrome"), Osteoporosis, Pancytopenia, chronic malabsorption/malnutrition, etc.; G-Tube; Currently TPN-dependent.
Meds: Zofran, Pulmicort, Heparin (to flush PICC line), IV Ceftazidime (for Pleural Effusion), Colloidal Silver (used topically).