Background: The impact of the introduction of the pneumococcal conjugate vaccine over antimicrobial resistance has not been well established. The present study models the changes in resistance over time for all major classes of antibiotics.
Methods: Susceptibility data on a total of 129,652 isolates from The Surveillance Network surveillance database during the period 1996-2007 were available for analysis, as well as age, specimen source, inpatient or outpatient location, and census region. Cubic splines in a logistic regression mixed model were used to model changes of the resistance rates over time in the United States, taking into account risk factors, so that separate adjusted curves were modeled for each antibiotic.
Results: Yearly resistance prevalence to most antibiotics had been increasing in the period 1996-2001. Adjusted prevalence rates in a multivariate model declined in the period 2001-2004 for penicillin, erythromycin, amoxicillin/clavulanate, trimethoprim/sulfamethoxazole, tetracycline, ceftriaxone, and multidrug. These same antibiotics showed a significant rebound for the period 2004-2007, with the largest overall increase for erythromycin, followed by amoxicillin/clavulanate, tetracycline, multidrug, penicillin, trimethoprim/sulfamethoxazole, and ceftriaxone. Changes in both decline and rebound were more marked for children <5 years old and for otitis media isolates.
Conclusion: The indirect effect of the pneumococcal conjugate vaccine introduction on yearly resistance prevalence for several antibacterials as well as for multidrug resistance is one of blunting of a prior sustained increase, with a significant but short-lived decrease in resistance rates, and a significant rebound in adjusted rates for the period 2004-2007.