This question is complicated, but I believe our years of experience with antibiotics offer some answers. Consider the effect of antibiotics during outbreaks of Salmonella infection. Antibiotic use actually increases the risk of Salmonella infection—presumably because normal bowel flora is disrupted and Salmonella can thrive. The same principle applies to Clostridium difficile disease. New strains that emerge can spread and we have to face new challenges in the management of this serious infection. We can also see this effect in patients who are at risk for resistant pneumococcal infection.
Children who take antibiotics select for resistant strains—for themselves, for their playmates, and for their parents and grandparents. This effect is somewhat reversed when vaccination of young children reduces the burden of both total infection and resistant infection. This benefit extends to parents and grandparents as well.
Clinicians sometimes prescribe long courses of preventive therapy for patients who have recurrent urinary tract infections. When "breakthrough" infections occur during therapy, the "bug" is often resistant to the old antibiotic.
Extreme cases occur with tuberculosis and HIV infection; resistant infections occur when patients take partial therapy. This sets the stage for selection of resis-tant subclones of the original pathogen.
—Thomas Fekete, MD
Section Chief, Infectious Diseases
Professor of Medicine Associate Professor of Microbiology and Immunology
Temple University School of Medicine