Superinfection

Superinfection is an infection that occurs during the course of another infection or after an initial infection, caused by a second microorganism. It often arises when antimicrobial therapy disrupts the normal microbial flora, creating ecological niches that allow opportunistic or resistant organisms to colonize and cause disease. By contrast, coinfection refers to two pathogens causing illness simultaneously, before substantial treatment has begun.

Common contexts include antibiotic-associated superinfection, where broad-spectrum antibiotics reduce microbial diversity and enable organisms such as Clostridioides difficile to proliferate and cause colitis. Other examples involve the emergence or overgrowth of resistant bacteria or fungi, such as Candida species, following antimicrobial therapy. In viral illnesses, secondary bacterial infections after influenza or other viral infections are a classic form of superinfection, contributing to increased morbidity and complicating clinical management.

Diagnosis typically relies on the clinical course in relation to the initial infection and targeted laboratory testing to identify the secondary pathogen. This may include cultures from suspected sites, molecular assays, and imaging studies to detect complications such as pneumonia or abscess formation.

Management involves treating the superinfection with appropriate, pathogen-directed therapy while continuing or adjusting treatment for the primary infection as indicated. Antimicrobial stewardship is important to minimize disruption of normal flora and reduce the risk of resistance. Prevention focuses on infection control practices, vaccination where available, and prudent use of antibiotics to preserve microbial balance and reduce the likelihood of superinfections.