Real-time PCR testing for mecA reduces vancomycin usage and length of hospitalization for patients infected with methicillin-sensitive staphylococci

Abstract

Nucleic acid amplification tests (NAATs) have revolutionized infectious disease diagnosis, allowing for the rapid and sensitive identification of pathogens in clinical specimens. Real-time PCR testing for the mecA gene (mecA PCR), which confers methicillin resistance in staphylococci, has the added potential to reduce antibiotic usage, improve clinical outcomes, lower health care costs, and avoid emergence of drug resistance. A retrospective study was performed to identify patients infected with methicillin-sensitive staphylococcal isolates who were receiving vancomycin treatment when susceptibility results became available. Vancomycin treatment and length of hospitalization were compared in these patients for a 6-month period before and after implementation of mecA PCR. Among 65 and 94 patients identified before and after mecA PCR, respectively, vancomycin usage (measured in days on therapy) declined from a median of 3 days (range, 1 to 44 days) in the pre-PCR period to 1 day (range, 0 to 18 days) in the post-PCR period (P < 0.0001). In total, 38.5% (25/65) of patients were switched to beta-lactam therapy in the pre-PCR period, compared to 61.7% (58/94) in the post-PCR period (P = 0.004). Patient hospitalization days also declined from a median of 8 days (range, 1 to 47 days) in the pre-PCR period to 5 days (range, 0 to 42 days) in the post-PCR period (P = 0.03). Real-time PCR testing for mecA is an effective tool for reducing vancomycin usage and length of stay of hospitalized patients infected with methicillin-sensitive staphylococci. In the face of ever-rising health care expenditures in the United States, these findings have important implications for improving outcomes and decreasing costs.

FIG. 1.

Vancomycin patient days for study patients before and after implementation of real-time mecA PCR. (A) Methicillin-sensitive S. aureus and methicillin-susceptible coagulase-negative staphylococcus isolates. (B) Methicillin-susceptible S. aureus isolates. (C) Methicillin-susceptible coagulase-negative staphylococcus isolates. (D) Methicillin-resistant S. aureus isolates. Wilcoxon's test was used to compare differences in medians (indicated by horizontal lines).

FIG. 2.

Time to vancomycin replacement for study patients infected with methicillin-sensitive isolates before and after implementation of real-time mecA PCR. Kaplan-Meier plot shows the cumulative percentage of patients on vancomycin therapy. Patients who were not switched to a different regimen are shown as censored. The P value computed with the Wilcoxon statistic is shown.

FIG. 3.

Hospitalization days for study patients infected with methicillin-sensitive staphylococci before and after implementation of real-time mecA PCR. Wilcoxon's test was used to compare differences in medians (indicated by horizontal lines).