Effects of MAC Preventive Therapy on Disease-Causing Bacteria in HIV-Infected Patients: A Substudy of CPCRA 048

Some people who have taken azithromycin to prevent MAC (Mycobacterium avium Complex, a bacterial infection common in HIV-infected persons) have been found to carry antibiotic-resistant bacteria (germs that grow despite the presence of drugs used to kill them). The purpose of this study is to see if people who take azithromycin carry more antibiotic-resistant bacteria than people who have chosen to delay MAC preventive therapy.

When bacteria like Streptococcus (a type of bacteria that causes pneumonia and meningitis) are frequently exposed to antibiotics, the bacteria can become resistant to the drugs. MAC preventive therapy uses antibiotics, but this can make it difficult to treat other infections caused by bacteria that have become resistant in HIV-infected persons. If MAC preventive therapy is delayed, Streptococcus in the body may be less likely to develop resistance. Therefore, if the patient does get a Streptococcus infection, it will be easier to treat because it is not resistant to the antibiotics.

Streptococcus pneumoniae is a leading cause of bacteremia, pneumonia, meningitis, and otitis media in the United States. Prior to 1987, this organism was uniformly susceptible to penicillin; since then, however, increasing numbers of isolates resistant to penicillin, as well as to other common antibiotics, have been identified. Frequent exposure to antibiotics has been documented as an important risk factor for the emergence of resistant organisms in HIV-infected patients, who are more likely than uninfected people to be colonized with antibiotic-resistant strains of S. pneumoniae. This substudy is the first to examine the effects of withdrawing or delaying the initiation of prophylaxis (in this case, MAC prophylaxis) on the prevalence of antibiotic-resistant pneumococci in a prospective manner.

Study participants are a subset of those enrolled in the CR-MAC Protocol (CPCRA 048). Oropharyngeal swabs are taken at baseline and 4 months after randomization, and are used to isolate S. pneumoniae in culture. These isolates are tested for susceptibility to macrolides, penicillin, cephalosporins, quinolones, and TMP-SMX. The rates of pneumococcal colonization at baseline and 4 months after randomization are determined and used to estimate the impact of deferring MAC prophylaxis on carriage of antibiotic-resistant S. pneumoniae.