Participants who experience an outbreak during the next year will be asked to call the clinic at the beginning of their next outbreak. The clinician will arrange to admit the participant to the UW General Clinical Research Center (GCRC) for a 5-day hospitalization stay. During hospitalization, participants will take acyclovir (400mg 3 times daily) and genital swabs will be collected every 2 hours during the day and every 4 hours at night for 5 days. After the last swab has been taken, the study nurse at the GCRC will do a final genital exam and the participant will be discharged. Some participants will also be asked to enroll in a control arm during which the same procedures will be followed except they will not take acyclovir during the recurrence.