Inclusion Criteria:  Age ≥18 years Currently hospitalized or in an emergency department with anticipated hospitalization.  Symptoms of acute respiratory infection, defined as one or more of the following:  Cough Fever (> 37.5° C / 99.5° F) Shortness of breath (operationalized as any of the following: subjective shortness of breath reported by patient or surrogate; tachypnea with respiratory rate ≥22 /minute; hypoxemia, defined as SpO2 <92% on room air, new receipt of supplemental oxygen to maintain SpO2 ≥92%, or increased supplemental oxygen to maintain SpO2 ≥92% for a patient on chronic oxygen therapy). Sore throat Anosmia Laboratory-confirmed SARS (Severe acute respiratory syndrome-Coronavirus 2 (SARS CoV-2) infection within 10 days prior to randomization Ability to manage own stool care  Exclusion Criteria:  Prisoner Pregnancy Breast feeding Current infectious or noninfectious diarrheal illness Unable to randomize within 21 days after onset of acute respiratory infection symptoms Unable to randomize after hospital arrival Colonic obstruction Unresolved hypovolemia CrCl <30ml/min Hypermagnesemia Diagnosis of Long QT syndrome Known allergy to magnesium citrate or probiotic Unresolved electrolyte imbalance such as hypokalemia or hypocalcemia. The patient can be enrolled if electrolytes are corrected and sustained. Receipt of >1 dose of magnesium citrate or any other colonic cleanser in the 7 days prior to enrollment Inability to receive enteral medications Refusal or inability to be contacted on Day 15 for clinical outcome assessment if discharged prior to Day 15 Concurrent medical illness that interferes with clinical assessment Previous enrollment in this trial The treating clinical team does not believe equipoise exists regarding the use of magnesium citrate plus a probiotic for the treatment of this patient. Participating in any other COVID-19 therapeutic trial Allergic to soy. Lactose intolerant.