[AS PER AMENDMENT 11/3/98: Up to 100 evaluable patients will now be studied. Group 2 is now modified to include up to an additional 15 evaluable patients with known MAC bacteremia and less than or equal to 7 days prior MAC treatment who are unable to commit to long-term follow-up (Group 2b); these patients will undergo only baseline evaluations. Group 2a consists of 15 evaluable patients with known MAC bacteremia and less than or equal to 7 days of prior MAC treatment who are willing and able to enter the follow-up phase.]