Opportunities to optimize care arise as new data from the microbiology lab become available. Understanding and using these data are critical towards the development of safe and appropriate treatment plans. In this article five moments for antimicrobial stewardship using microbiology results are discussed.
Authored By: Timothy Gauthier, Pharm.D., BCPS-AQ ID
[Last updated: 14 March 2019]
Earlier this year three top infectious diseases physicians published an excellent article in JAMA that discusses incorporating four moments of antibiotic decision making into clinical practice. You can find the article here.
Inspired by the title of the work from these thought leaders, I have composed a simple dialogue on moments for antimicrobial stewardship using microbiology results. These are moments in time when new data allows for re-evaluation of existing clinical scenarios. Following such re-evaluation, action may or may not be indicated.
This is intended to be a basic article with an objective to discuss a few of the key considerations that come up in clinical practice every day across the globe as new data become available from microbiology laboratories.
Here are five moments for antimicrobial stewardship using microbiology results…
1. When a culture result is updated as still being negative
While a specimen is being held for culture in the microbiology laboratory it is common for staff to periodically evaluate it for microbial growth. Practices can vary, but culture specimens are typically assessed at least every 24 hours, updating lab reports accordingly. If nothing grows after the set period of time that culture type is held for (for example 5 days), then the microbiology lab report will be finalized as no growth.
This means that if a culture is ultimately finalized as negative after 5 days of observation, each day up until that point the report for that specimen will be updated to say something such as “no growth after 24 hours” then “no growth after 48 hours” and so on. The final report at day five would say something along the lines of “final report – no growth.”
Some clinicians may argue that they want to continue empiric antimicrobial therapy until the cultures are finalized as negative and only then will they discontinue them. In some instances this can be a reasonable course of action, however this is infrequently the case.
Each day when a microbiology report is updated and found to still be negative, this offers an excellent moment to think about antimicrobial stewardship. Four questions to ask at this time can be:
- Can other information we have now that we did not have before explain this patient’s medical problem?
- Does this patient even need antibiotics at this point?
- If this patient does need antibiotics, are they on the right one(s) still?
- Have there been any clinical changes that indicate my antibiotic dose today needs adjustment?
Remember not to just take note when “culture is positive at day 3” is reported, but also when “culture remains negative at day 3” is reported.
2. When a culture comes back positive
When a culture returns positive it is all too common for people to start referring to it as an infection. For example, instead of saying “the positive urine culture” people might say “the UTI.” Just because something is growing in the microbiology lab, does not necessarily mean someone has an infection. Beware knee-jerk reactions and a desire to act because something is positive.
At the moment when a positive culture is reported it is essential to first ask:
- Does this represent colonization, contamination, or infection?
Until this question is answered, discussions about picking drugs, doses, and durations are largely inconsequential if not academic. If the culture is positive and the patient is indeed found to have an active infection, it is time to re-evaluate their antimicrobial drug regimen, dosing, and monitoring plan.
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3. When rapid molecular diagnostics identify an organism and/or resistance gene
Rapid molecular diagnostic tests have revolutionized the field of clinical microbiology because they can identify organisms and the presence of antimicrobial resistance genes much faster than conventional microbial identification and susceptibility testing techniques. This can mean information is available up to ~48 hours earlier for patient care decisions.
While new rapid molecular diagnostic tests come into use in clinical practice, it is important for end users to be familiar with them so that results generated produce a clinical benefit for patients.
Providers may be accustomed to seeing reports from the microbiology lab in a certain format and may only look for them at certain times of the day. Being aware of when to look for results and knowing how to interpret the results is important. So for example when you find out “MecA negative Staphylococcus aureus cultures identified by PNA FISH, sensitivities in process” has been resulted, consideration can be given as to whether any anti-MRSA or anti-Gram negative therapy a patient is receiving is still warranted since MSSA has now been identified.
Numerous publications have identified that combining antimicrobial stewardship efforts with rapid molecular diagnostic results can be fruitful, however people not on the core antimicrobial stewardship team can certainly also make an impact as these new lab results become available.
4. When a full sensitivity profile is reported
Initially microbiology laboratories will report preliminary findings on positive cultures such as bacteria morphology and growth characteristics (e.g., alpha haemolytic gram positive cocci in pairs or non-fermenting Gram negative rods). Eventually for positive cultures, the organism will be identified and a full sensitivity profile is reported.
This is the moment to assess which agents are preferred, contrast those drugs with the individual clinical scenario you are faced with, and pick the right drug for that bug.
For example, if a culture is found to be Enterococcus faecalis that is sensitive to all of the antibiotics for which it was tested against, most clinicians would first look to ampicillin, then vancomycin, then daptomycin or linezolid. Some labs report minimum inhibitory concentrations (MICs). What if the MIC for daptomycin is lower than the MIC for ampicillin? Does this mean daptomycin will be a better drug for killing the bacteria? The answer to this is no. It is inappropriate to select an antimicrobial based off of an MIC comparison when all of those drugs have been found to be effective. This is actually the reason many microbiology labs do not report MICs – so people will not just pick the lowest number!
Use this moment to pick the right drug for the bug. Sometimes this will require some research on uptodate.com, pubmed.com, or by consulting with a specialist.
5. When something does not look right
When a microbiology lab result seems unusual it is a good time to pick up the phone and talk to the people working in the lab. Sometimes results are reported in a way that is not consistent with how the same finding has been previously reported. Sometimes human errors are made.
When something does not look right, take a moment to speak with the folks from the lab and do a spot check on the system. Not only may you discover the answer to your question, you may also make a new friend out of one of the incredibly talented and capable people working in the lab!
Closing comments
As microbiology results are reported be sure to keep your proverbial antimicrobial stewardship hat on firm to ensure the appropriate and safe use of antimicrobial agents in your patients. As you do this do not forget that it is teamwork that makes the dream work, and when the team works the patients win.
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