To evaluate the micro-biologic efficacy and safety of a streamlined treatment for early onset methicillin-resistant staphylococcus aureus (MRSA) in patients with cystic fibrosis.

This is an open-label, multi-center interventional trial in Cystic Fibrosis (CF) patients with new MRSA isolated from the respiratory tract (oropharyngeal (OP) = OP swab, sputum, or bronchoscopy) at a clinical encounter. Forty-two subjects with new MRSA infection will be enrolled and will receive two weeks of oral trimethoprim-sulfamethoxazole (TMP-SMX) or minocycline depending on age, allergies and antibiotic resistance of prior isolate for 14 days, and nasal mupirocin for 5 days. Subjects old enough to do so will use oral disinfectant gurgle (0.12% chlorhexidine gluconate oral rinse) for 14 days. The primary endpoint will be the proportion of positive MRSA respiratory cultures at Day 28 and this will be compared to our prior STAR-Too results. Subjects will then have a 14 day wash-out period (i.e., no TMP-SMX or minocycline from Day 14 to Day 28) and all participants will repeat the treatment protocol from Day 29 to Day 42. Repeat cultures will be done at day 56 ± 7 days, most likely combined with their next clinic visit. Results of Day 56 cultures will be an exploratory, secondary outcome. A subsequent visit will be 3 months later with their routine clinic appointment. Any interim clinic visits will be used to obtain repeat cultures and clinical data. Assessment of MRSA culture status will be by OP swab for all subjects, with additional sputum in those who expectorate. Total duration of an individual subject's participation will be six months. Total duration of the study is expected to be 42 months, which includes data analyses and publication. Due to COVID 19 restrictions, a study amendment was filed in March 2020 for subjects currently active subjects that allowed remote study visit for V3 and V4. Cultures were collected at home and mailed to the Core Study lab, clinical case forms and surveys were completed via video visits. These changes were approved by each study site that this was relevant to i.e. 4 study sites had subjects active at that time.