Effect of Lactobacillus on the Microbiome of Household Contacts Exposed to COVID-19

Inclusion Criteria: * Age \>=1 year (as children \<1 year may not be able to take oral probiotics) * Household contact of someone diagnosed with COVID-19 * Willingness to stop taking other probiotics or to not take any other probiotic while on LGG/placebo (taking a probiotic at the time of screening will not be considered a reason for exclusion. However, subjects will be asked to stop taking their probiotic if they enroll on the study). * Access to e-mail/internet to complete electronic consent via REDCap Exclusion Criteria: * Symptoms of COVID-19 at enrollment, including: * Fever * Respiratory symptoms * GI symptoms * Anosmia * Ageusia -\>7 days since original patient associated with household contact was diagnosed with COVID-19 * Taking hydroxychloroquine or remdesivir for any reason (as this would have the potential to decrease the expected rate of COVID-19 in this population and affect our power and sample size calculations) * Enrolled in a COVID-19 prophylaxis study (as this would have the potential to decrease the expected rate of COVID-19 in this population and affect our power and sample size calculations) * Any medical condition that would prevent taking oral probiotics or increase risks associated with probiotics including but not limited to: * Inability to swallow/aspiration risk and no other methods of delivery (e.g., no G/J tube) * Increased infection risk due to immunosuppression due to: * Chronic immunosuppressive medication * Prior organ or hematopoietic stem cell transplant * Known neutropenia (ANC \<500 cells/ul) * HIV and CD4 \<200 cells/ul * Increased infection risk due to endovascular due to: * Rheumatic heart disease * Congenital heart defect, * Mechanical heart valves * Endocarditis * Endovascular grafts * Permanent endovascular devices such as permanent (not short-term) hemodialysis catheters, pacemakers, or defibrillators * Increased infection risk due to mucosal gastrointestinal due to: * Gastroesophageal or intestinal injury, including active bleeding