Clinical Microbiology and Infection Prevention are Essential Partners

ICT: Has your facility seen a spike in HA-MRSA and CA-MRSA cases? Have timely antibiograms helped clinicians switch from empiric treatment to more tailored antibiotic prescribing and other treatment?

JH: We do not perform any tests that definitively differentiate HA-MRSA from CA-MRSA, however like many others, we have seen increases in our rates of MRSA that peaked in 2004 and have remained relatively stable over the past four years. This holds true for isolates from both inpatients and outpatients. With the percentages of Staphylococcus aureus that are MRSA hovering around 40 percent to 60 percent in most U.S. facilities, a physician would rely on laboratory tests to rule out MRSA in patients with suspected staphylococcal infections prior to prescribing agents that do not cover for MRSA. Analysis of susceptibility test results on a subset of S. aureus that only includes MRSA isolates could help guide use of anti-MRSA drugs. For example, if the percentage of MRSA susceptible to clindamycin among outpatients is high, clindamycin might be empirically prescribed for suspected staphylococcal infections.

ICT: How can clinicians best use cumulative antimicrobial susceptibility test data to make sound clinical decisions?

JH: Laboratories should have the ability to not only produce an annual cumulative antimicrobial susceptibility test data report (e.g., cumulative antibiogram) but also to extract additional data to answer specific questions as they arise in order to support empiric prescribing practices. For example, with increasing fluoroquinolone resistance among gram-negative bacilli, an emergency room may wish to know if fluoroquinolone resistance rates for E. coli isolates from urine are the same among all age groups. Having these data could assist a facility to develop a protocol for empiric therapy of cystitis in outpatients that might differ for various age groups. It is not uncommon to find higher rates of fluoroquinolone resistance among isolates from elderly patients. For another example, an ICU might wish to know the percentage of Pseudomonas aeruginosa isolates that are susceptible to either tobramycin or piperacillin-tazobactam or both agents to help guide empiric therapy decisions. If the percentages of susceptible isolates are low, they may wish to examine data for alternative combinations of drugs.

The annual cumulative antibiogram generated by most facilities includes isolates tested from all types of patient populations. Although this may help answer some questions to guide empiric therapy of initial infections, more refined analyses are generally more useful. To expand the use of cumulative antibiogram data we need to: 1) ensure all laboratories have the technology to easily analyze antimicrobial susceptibility data in a variety of ways and in a timely manner; 2) work with clinicians to identify those data that would be most useful in guiding empiric therapy decisions; and 3) educate those involved with antimicrobial therapy about the value of cumulative antibiogram data.