A superinfection is a new infection that develops on top of an existing one, often during or after treatment of the original infection, usually because the initial therapy disrupts normal flora or selects for resistant or opportunistic pathogens.
Explanation
Superinfection occurs when the conditions created by a primary infection and its management enable a different pathogen to establish itself. Broad‑spectrum antibiotics that suppress a wide range of bacteria can eliminate commensal populations and create ecological niches for resistant organisms or fungi to overgrow. Immunocompromised states from the first infection or its treatment can also facilitate invasion by new pathogens. In virology, superinfection refers to infection of an already infected cell or host with a second strain of the same or a different virus, which can result in genetic recombination or interference. Superinfection should be distinguished from a secondary infection: secondary infections often follow an initial illness as a result of tissue damage or immune suppression, whereas superinfection emphasises the selection of resistant or opportunistic microbes during antimicrobial therapy. Recognising superinfection is important because it may require cessation of the offending antibiotic, initiation of targeted therapy and implementation of infection‑control measures.
Clinical and virological examples
A classic example is Clostridioides difficile colitis that arises in patients treated with broad‑spectrum antibiotics for pneumonia or urinary tract infections; the antibiotic suppresses normal gut flora and allows toxin‑producing C. difficile to proliferate. Oral candidiasis developing during inhaled corticosteroid therapy or after antibacterial treatment is another superinfection. In hospitals, patients receiving vancomycin for methicillin‑resistant Staphylococcus aureus may develop vancomycin‑resistant enterococcal superinfections. In virology, hepatitis D virus requires hepatitis B virus for replication and can cause a severe superinfection in someone chronically infected with hepatitis B. Infection of an HIV‑positive individual with a second, distinct HIV strain can lead to recombinant viruses and complicate antiretroviral treatment. Superinfection in bacteriophage biology describes infection of a bacterium already lysogenised by one phage with another, which can lead to lysogenic conversion or be blocked by superinfection exclusion mechanisms.
Superinfections underscore the need for judicious use of antimicrobials and careful monitoring of patients for opportunistic or resistant pathogens during therapy.
Related Terms: Secondary infection, Coinfection, Antibiotic resistance, Opportunistic pathogen, Viral recombination.