Superinfections

Superinfection is an infection caused by a pathogen different from the one initially responsible for illness, typically occurring during or after treatment of the primary infection. It often results from disruption of the normal microbiota, enabling overgrowth of resistant or opportunistic organisms, or from immune suppression. The term is sometimes used interchangeably with secondary infection or, less precisely, coinfection, but in many contexts it emphasizes a new pathogen arising during therapy.

Common examples include antibiotic-associated superinfections such as Clostridioides difficile infection after broad-spectrum antibiotic use, and oral or vaginal candidiasis due to disruption of bacterial flora. More rarely, patients may acquire bacteremia or pneumonia from organisms that capitalize on hospitalization, indwelling devices, or prior antibiotic exposure. Viral superinfections, such as secondary bacterial pneumonia following influenza, are also described, particularly in vulnerable patients.

Pathogenesis involves depletion or imbalance of commensal bacteria, impaired host defenses, or colonization by resistant strains. Risk factors include broad-spectrum antibiotic therapy, immunosuppression, advanced age, comorbidities, hospitalization, and invasive procedures.

Diagnosis relies on new or worsening symptoms that cannot be explained by the initial illness, and is confirmed by targeted microbiological testing. Management requires treating the new pathogen with appropriate antimicrobials while reassessing the need for current therapy; in conditions like C. difficile infection, specific guidelines exist for toxin-mediated disease. Prevention focuses on antimicrobial stewardship, minimizing broad-spectrum antibiotic use, infection control, and vaccination where applicable.

Prognosis varies and depends on the organisms involved, comorbidity burden, and timeliness of treatment.