The Real Promise of Precision Antimicrobial Therapy in Emergency Medicine

Article

Precision medicine has transformed fields such as oncology by increasingly matching treatment to the molecular characteristics of an individual patient's disease. Infectious disease appears poised for a similar transition. Rapid molecular diagnostics, host-response assays, resistance-gene detection and accelerated antimicrobial susceptibility testing are beginning to provide clinicians with information that once required days to obtain. For emergency medicine, however, precision antimicrobial therapy presents a unique challenge: sometimes treatment cannot wait for precision. A patient presenting in septic shock illustrates the problem. The emergency physician must simultaneously stabilize the patient, identify the likely source of illness, obtain appropriate cultures and initiate effective antimicrobial therapy. The consequences of delaying treatment for a serious bacterial infection can be substantial. Yet the initial clinical presentation of sepsis can overlap with viral illness, inflammatory disease, pancreatitis, medication reactions and numerous other noninfectious conditions. This creates one of the central dilemmas of antimicrobial care: the patients in whom unnecessary antibiotics are most concerning are not necessarily the patients in whom clinicians can safely wait to achieve diagnostic certainty. Precision Medicine Meets an Asymmetric Risk Much of the discussion surrounding rapid infectious-disease diagnostics assumes that faster identification will allow clinicians to avoid empiric broad-spectrum antibiotics. That may be true for selected patients, but it is unlikely to become the dominant strategy for patients presenting with shock or other manifestations of severe infection. The reason is not simply technological. It is clinical. Diagnostic decisions are influenced by the consequences of being wrong. Giving several doses of broad-spectrum antibiotics to a patient subsequently determined not to have a bacterial infection has consequences: adverse drug effects, disruption of the microbiome, Clostridioides difficile infection and selective pressure contributing to antimicrobial resistance. But failing to treat bacterial septic shock carries an entirely different magnitude and immediacy of risk. Even an excellent diagnostic test must therefore clear a very high evidentiary threshold before clinicians will use a negative result to withhold initial antimicrobial therapy from a critically ill patient. This is an important distinction because it changes what we should expect precision diagnostics to accomplish. Precision Does Not Have to Begin With the First Dose The greatest near-term opportunity may not be eliminating empiric antimicrobial therapy. It may be dramatically shortening its duration. For decades, clinicians have accepted a frustrating reality. We begin treatment based primarily on clinical probability, obtain cultures and then wait. Organism identification and conventional antimicrobial susceptibility testing gradually provide the information necessary to narrow therapy. Precision diagnostics have the potential to compress this cycle. Host-response technologies may provide information about whether the patient's immune response is more consistent with bacterial or viral infection. Multiplex molecular assays can identify pathogens and selected resistance determinants. Emerging sequencing approaches can broaden the range of organisms that can be detected. Rapid phenotypic susceptibility testing can potentially determine whether an organism actually responds to a particular antimicrobial far sooner than conventional workflows. No single technology necessarily provides the entire answer. Together, however, they can progressively reduce uncertainty. That changes the therapeutic objective. The first antimicrobial decision may still be empiric. The second should be better informed. The third should be better informed still. The goal of precision antimicrobial therapy should be to make every subsequent dose more precise than the one before it. From Days of Uncertainty to Hours This is where rapid diagnostics could have their greatest impact on antimicrobial stewardship. The traditional model can leave patients receiving broad-spectrum therapy while clinicians wait 24, 48 or even 72 hours for sufficient microbiologic information to confidently narrow treatment. The precision model seeks to move clinically actionable information much earlier in that timeline. A patient might appropriately receive broad-spectrum antibiotics during initial resuscitation. Hours later, new diagnostic information could indicate that MRSA coverage is unnecessary, identify a resistance mechanism requiring a different agent, support narrowing therapy to a specific pathogen or strengthen the conclusion that bacterial infection is unlikely. The stewardship benefit is therefore not limited to whether antibiotics were administered. A more meaningful metric may be hours of unnecessary antimicrobial exposure avoided. Preventing two days of unnecessary broad-spectrum therapy may ultimately be more realistic—and more clinically consequential—than attempting to prevent the first dose in a critically ill patient. The Emergency Department Is Not One Risk Population There is also an important distinction between septic shock and possible infection in a stable patient. Emergency physicians evaluate a large population of patients in whom infection is plausible but far from certain. Fever, tachycardia, leukocytosis and elevated inflammatory markers are not specific for bacterial infection. In a hemodynamically stable patient, clinicians may have time to obtain additional diagnostic information before committing to antimicrobial therapy. This may ultimately be where some precision diagnostics have their greatest effect on antibiotic initiation rather than de-escalation. The same test result can therefore have very different clinical significance depending on the patient receiving it. A negative bacterial host-response signature in a stable patient with an ambiguous presentation may meaningfully lower the probability of infection and influence the decision to withhold antibiotics. The identical result in a patient with profound hypotension and rapidly progressive organ dysfunction may appropriately carry far less weight. Precision medicine is not simply about obtaining more precise molecular information. It is about interpreting that information in the context of the individual patient. A New Definition of Precision Antimicrobial Therapy The future of antimicrobial care in emergency medicine will probably not be a single test that identifies the correct antibiotic before treatment begins. It is more likely to be an increasingly integrated diagnostic system. Clinical phenotype establishes the initial probability of infection. Host-response testing helps characterize the patient's biological response. Molecular diagnostics identify pathogens and resistance determinants. Rapid susceptibility testing determines which drugs are actually effective. Clinical decision support integrates these findings with prior microbiology, allergies, organ function, local resistance patterns and the patient's physiologic condition. With each layer of information, the therapeutic field narrows. That is precision antimicrobial therapy. The objective is not to eliminate empiricism from emergency medicine. Emergency physicians will always encounter situations in which treatment must begin before all of the information is available. The opportunity is to make empiricism temporary. If emerging diagnostics can compress the period between “we need to treat now” and “we know what this patient actually needs” from days to hours, they could simultaneously improve antimicrobial stewardship and preserve the urgency required to treat life-threatening infection. In emergency medicine, that may prove to be the most important form of antimicrobial precision.