Evidence-Based, Economical Diagnostics

Physicians in direct patient care, regardless of specialty, regularly perform infection diagnostics. But how do you avoid diagnosing too little or too much? Which diagnostic steps are cost-effective and benefit patients?

This article lays out practical solutions to common infectious-disease questions encountered in everyday clinical practice.

Clinical Question: Wound Swab

A patient with diabetes presents with fever, general malaise, and a superficial ulcer on the foot. There is no surrounding erythema. He cannot recall any significant trauma.

You know that superficial wounds without signs of an acute inflammatory reaction are unlikely to explain systemic symptoms. You refrain from taking a wound swab because it cannot distinguish colonization from infection. Pseudomonas aeruginosa and Staphylococcus aureus, among other organisms, colonize moist surfaces once the epithelium is breached. Most open wounds, therefore, become colonized by a polymicrobial flora.

You also withhold antibiotics because they do not promote wound healing if no infection is present. Instead of immediate antibiotic therapy, you initiate an investigation of underlying causes. Diabetes, arterial insufficiency, or venous insufficiency could underlie the wound.

Clinical Question: Urinary Tract Infection

A patient with a urinary catheter presents with fever, malaise, rapid breathing, and slightly darkened urine. You want to determine whether a catheter-associated urinary tract infection (CAUTI) is present.

Because the symptoms of a CAUTI are often nonspecific, diagnosis is challenging. A urine test strip should be avoided because a catheter is in place and, according to studies, leukocyte results in such cases have only a weak correlation with infection. Furthermore, pyuria also does not distinguish asymptomatic bacteriuria from a CAUTI.

Instead, you send a urine sample drawn from the catheter to the laboratory. You know a catheter is not sterile and expect colonization with bacteria from the perineum. Studies show the incidence of bacteriuria is 3%-8% per catheter day. After a month, almost every sample would therefore be positive. You will interpret the results in the context of the clinical picture.

You withhold empirical antibiotics because the patient is stable and has only nonspecific symptoms. Unnecessary antibiotics drive antimicrobial resistance and expose the patient to antibiotic side effects and Clostridioides difficile-associated diarrhea.

Clinical Question: Treating Methicillin-resistant Staphylococcus aureus (MRSA)

MRSA was detected in a wound of one of your hospitalized patients during routine screening.

You do not panic or start systemic treatment solely because of a screening result. You interpret a screening test differently from a clinically indicated diagnostic test. You place the patient in isolation and follow guidelines for decolonization. You do not start antibiotic therapy.

If the same patient later develops an infection, your background knowledge will influence therapy. If, for example, he develops severe cellulitis, you would initiate intravenous administration of vancomycin because you know he is colonized with MRSA.

Clinical Question: Drawing Blood Cultures

A patient presents with fever and general malaise. After nondiagnostic routine testing, you draw blood cultures.

You know from studies that it is acceptable to obtain two blood culture sets drawn from the same arm. Previously, it was thought that sampling from two separate sites offered a diagnostic advantage.

You also know that between 0.6% and 6% of all positive blood-culture results are due to contamination. Staphylococcus epidermidis is often involved; it is commonly found on human skin and can be introduced into the blood by needle puncture. Therefore, when interpreting results, you look for clinical correlation.

If repeat testing detects coagulase-negative staphylococci, you interpret the result differently than you would the first time. Studies also show that the likelihood that a positive result represents contamination falls from 75.2% to 27.8% when two blood culture sets grow the organism.

Clinical Question: Infected Medical Devices

An infection has been detected on the pacemaker of one of your patients. You know that the correct course of action depends on the pathogen’s virulence, its potential for biofilm formation, the device material and function, whether a procedure is required to remove the device, and the patient’s health and preferences. You therefore discuss options with the patient and consult cardiology about possible endocarditis or a device-associated infection. You involve the hospital’s clinical microbiology and infectious-disease departments. Together, you develop an individualized treatment plan.

Conclusion

Correct infectious-disease management is often hard to identify in everyday clinical practice. Although a specialty exists for these questions, physicians in many other disciplines must make relevant decisions every day. The high prevalence of multimorbidity, complex medical devices, the need for cost-effectiveness, prevention guidelines, and other factors complicate decision-making.

A useful guiding principle for noninfectious-disease specialists when choosing an approach is to critically question the clinical consequences of a diagnostic test or therapy before ordering or starting it.

This story has been translated from Univadis Germany, part of the Medscape Professional Network.