The Value of Diagnostics: The Impact of Hospital Antimicrobial Susceptibility Testing

The number of U.S. hospital discharges in which there was a diagnosis of infection with drugresistant microorganisms increased more than one hundred-fold between 1993 and 2005. Among the concerns over drug-resistant microorganisms is the rapid increase in the incidence of such infections acquired by patients within the hospital or healthcare setting. Infectious disease experts have argued that tests that reveal the susceptibility of the infecting agent (pathogen) to antimicrobial agents can allow physicians to administer more appropriate and effective treatments. Further, experts also suggest that such tests are essential in identifying healthcareacquired infections and bringing them under control, with resulting positive patient outcomes, savings in costs, and improved quality. In this paper, we perform an econometric analysis of the impact of antimicrobial susceptibility testing on the survival, length of stay, and treatment costs of inpatients with staphylococcal infections, based on a large sample of U.S. hospital admissions during 2004 – 2005. We test the hypotheses that patients infected with staphylococci in the hospital inpatient setting whose pathogens were isolated and tested for antimicrobial susceptibility had lower hospital mortality rates, length of stay, and overall treatment costs than patients whose isolates were not tested, controlling for a number of indicators of the nature and severity of illness. The analysis is performed using data on two different patient populations: 1. Patients with a secondary diagnosis related to a Staphylococcal infection; and 2. Patients with any infectious & parasitic disease diagnosis (primary or secondary) The analysis indicates that, within both populations, infected patients whose etiologic agent (pathogen) was tested for antimicrobial susceptibility had significantly lower inpatient mortality rates, lengths of stay, and overall treatment costs than infected patients whose pathogens were not tested, controlling for principal diagnosis, number of diagnoses, number of procedures, age, and sex. Among patients in the first group—patients with a secondary staphylococcal infection diagnosis – those who had isolates tested for antimicrobial susceptibility had 52% lower probability of death before discharge, 17% lower mean length of stay (-1.8 days), and 22% lower cost than those who did not. Antimicrobial testing in this group was associated with $6,978 lower cost per discharge. The potential aggregate cost reduction from antimicrobial susceptibility testing of isolates from all patients hospitalized with this diagnosis in 2005 was $8.3 billion. Among the patients in the second group—patients with any infectious & parasitic disease diagnosis—those who had isolates tested for antimicrobial susceptibility had 30% lower probability of death before discharge, 26% lower mean length of stay (-1.8 days), and The Value of Diagnostics: The Impact of Hospital Antimicrobial Susceptibility Testing 2 36% lower cost than those who did not. Antimicrobial susceptibility testing in this group is associated with $7,524 lower cost per discharge. It is possible that the overall quality of care received by patients who had isolates tested for antimicrobial susceptibility was better than the overall quality of care received by patients who did not, and that part of the observed differences in mortality, length of stay, and cost are due to unobserved differences in treatment quality. But since the differences in outcomes and expenditure are so large relative to the cost of testing, administering antimicrobial susceptibility tests would be worthwhile even if it accounted for a very small fraction of the observed differences in mortality, length of stay, and cost. Frank R. Lichtenberg, Ph.D. Courtney C. Brown Professor of Business Columbia University 614 Uris Hall 3022 Broadway New York, NY 10027 Phone: (212) 854-4408 [email protected] The Value of Diagnostics: The Impact of Hospital Antimicrobial Susceptibility Testing