PHAGEFORCE is a prospective, observational registry study. The University Hospitals Leuven has approved the application of phage therapy as standard-of-care only in patients for whom no curative treatment alternatives (antibiotic and/or surgical) are available ('last-resort cases'). A multidisciplinary phage task force, referred to as the Coordination group for Bacteriophage therapy Leuven (CBL) was set up. The CBL screens patients with difficult-to-treat infections, evaluates who could benefit from phage therapy and sets up the treatment protocol. With this study, the CBL aims to gain insight in the safety and efficacy of phage therapy by integrating and optimizing phage therapy in five distinct medical disciplines (with distinct routes of administration), facilitating long-term follow-up of patients. Furthermore, this study will gain insight in the biodistribution and exact mechanisms of action of phage therapy and thus be able to provide standardized guidelines for each patient population and route of administration.

Patients with difficult-to-treat musculoskeletal infections, chronic rhinosinusitis, sepsis, pulmonary infections associated with cystic fibrosis or bronchiectasis, or hidradenitis suppurativa, for whom no standard (curative) treatment options are available, are eligible for phage therapy. Patient eligibility is evaluated by the Coordination group for Bacteriophage therapy Leuven. If phages are available against the isolated bacterial species and the patient is found eligible for phage therapy, a phagogram is performed. Solely based on the results of the phagogram, the patient is either included in the phage treated or control group (standard (non-curative) treatment). In both cases, data is collected using REDCap.

Inclusion Criteria:

All patients:

• Diagnosed with a musculoskeletal infection or chronic rhinosinusitis or sepsis or lung infection (CF/Bx) or hidradenitis suppurativa, and
• For whom all previous treatments (surgical and antibiotic) have failed or for whom no other treatment options are available (i.e., last resort cases, based on the assessment of the CBL), for example in case of bacterial resistance. And
• Of whom the pathogen causative for the infection is one for which phages are available in the phage bank, and
• Who have given informed consent to have their data collected in a patient registry

Exclusion Criteria:

All patients:

• With an infectious disease other than those mentioned above, and/or
• For whom standard treatment alternatives are still available. And/or
• Of whom the pathogen causative for the infection is not one for which phages are available in the phage bank. And/or
• Who refused to give their informed consent

All patients with a musculoskeletal infection or sepsis or chronic rhinosinusitis or pulmonary infection (associated with bronchiectasis or cystic fibrosis) or hidradenitis suppurativa for whom all previous treatments (anti-inflammatory/antibiotic/surgical) have failed or are likely to fail, or for whom no other treatments are available (i.e. in case of antibiotic resistance).