Beyond the Hospital Antibiogram: Digging Deeper to Guide Therapy for HABP/VABP

Antibiograms are great guides for initial empiric antibiotic therapy. They provide an aggregate snapshot of the degree of antimicrobial resistance among pathogens circulating in your hospital. If you don’t know what pathogen you are dealing with, the antibiogram can inform you about patterns of resistance and can guide empiric therapy to treat the patient with the right drug and improve outcomes.

With Antibiograms, the Narrower, the Better
At my health system in Miami, we implemented a process to distribute to all the medical staff hospital-wide antibiograms over 14 years ago and we update them once per year. We also perform hospital (adult vs pediatric), unit-specific (medical intensive care unit [ICU] vs emergency department [ED]) and source-specific (urine vs blood) antibiograms. They are very labor intensive. Drilling down to get more detailed information, these antibiograms that are specific for each of the ICUs give a better picture of their bacterial flora and patterns of antimicrobial resistance. For example, organisms and susceptibilities in our trauma ICU might be very different from those in the transplant, surgical, or medical ICUs. Patients have different risk factors, sources of infections, immunity and antimicrobial use patters, thus a more specific antibiogram is ideal to optimize empiric therapy especially in sepsis.

Our teams also collect antibiograms by body site and hospital department. For example, for urinary tract infections (UTIs) in the emergency department, we have urine-specific antibiograms because the bacteria causing a community-acquired UTI are going to be very different than the bacteria from a UTI in someone who has been in a nursing home or the hospital with a catheter for 3 months.

In terms of hospital-acquired or ventilator-associated bacterial pneumonia (HABP/VABP), respiratory-specific antibiograms are very challenging as these are “nonsterile” sites, in my opinion. We don’t have such antibiograms because we would need to differentiate between true infection and colonization, which requires manual chart review of thousands of patients, something that is not always feasible. Finally, not all patients with HABP produce sputum or are intubated to collect respiratory cultures.

Beyond Empiric Therapy, Look to Other Sources of Information
But there are some limitations with antibiograms. They pretty much capture the first organism within a specimen from a patient. Imagine a patient gets admitted to the hospital with a trauma. On admission, when you take that respiratory culture, her flora is the community flora. But if the patient is then ventilated for 2 weeks, her flora or the antimicrobial susceptibilities will change. A respiratory culture taken after 2 weeks on the ventilator will have a different pattern of resistance than at admission because the patient has been exposed to medications and the hospital. At a later date, that flora will change again. So, the problem is that the hospital antibiogram captures the first isolate within a specimen per patient, per admission. You also need to look at the data in aggregate, but most importantly to the individual patient, their antimicrobial history, risk factors, and patterns of antimicrobial resistance.

I will ask if we have surveillance cultures for this patient who has been here for 4 weeks. If yes, I might know by surveillance that this patient is already colonized with a multidrug-resistant organism. Get a good medical history, examine the patient, look at that original admission culture, antimicrobial history, previous hospitalizations or ED visits if available, and then I look at what the patient is growing now. With that information, I start shifting my therapy for her.

It is important to emphasize that I don’t only look at the cultures —I also look at the patient’s travel, hospitalization, and treatment history. Previous exposure to antibiotics is a risk factor for antimicrobial resistance, it will help me decide what the best treatment is today, not when she was admitted 4 weeks ago. With molecular diagnostics and culture results, we now have more information and we can de-escalate or escalate therapy to optimize the management of the infection she has today.

Automatic Testing Algorithms Save Time and Avoid Treatment Delays
At our institution, we implemented an algorithm that is used up-front, based on rapid testing, which automatically triggers more detailed testing depending on the first result. We did this because it was burdensome and a source of treatment delays for our physicians and pharmacies to call the lab after a treatment failure, then for the lab to retrieve the plate and re-test after several days (sometimes the cultures were no longer available!). With the algorithms, we tell the lab, “When you see these patterns of resistance, we need you to automatically start testing against these antibiotics because that will help us determine what should be the next drug to use, based on the pattern of resistance.” This saves time and guides empiric therapy much faster and improves patient care.

From a stewardship standpoint, my key points to remember are to know your patient’s medical history, a good physical exam to understand the source of infection, review your patient’s previous antibiotic use, and know your local epidemiology by working closely with the microbiology lab so you can look at specific patterns of resistance and therapeutic options. Antibiograms are one more tool for identifying antibiotic resistance patterns in your hospital, unit or health system, but one has to provide precision medicine and look at the individual patient to provide the best quality of care.

Your Thoughts
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