Melissa is a 35-year-old mother of three who works in marketing. She is being seen in consultation by the Internal Medicine service while admitted to Thoracic Surgery for an empyema. Three months prior she began to have cough with intermittent fevers and chills. She has been treated as an outpatient by her family doctor with Amoxicillin, Azithromycin and Levofloxacin over this time. Her symptoms would initially improve but would return within days of completing her antibiotic course. Her condition continued to worsen until this admission. On review of her past history, she has chronic facial pain and pressure with frequent purulent discharge, and typically has 2-3 sinus infections per year requiring antibiotics. She has never had pneumonia before this year. She has never received pneumococcal vaccination. She received her childhood immunization series and had her last tetanus and diphtheria booster 4 years ago. She has been re-vaccinated for measles, mumps, rubella twice, after prenatal evaluation deemed her non-immune. Prior to onset of these symptoms, her only medication was the oral contraceptive pill. In addition to leaving recommendations to manage her empyema, you wonder about her history of recurrent sinusitis and recent pneumonias. As such, you order some screening bloodwork.