Coinfection
Coinfection is when a person is infected by more than one pathogen at the same time. This can happen with different viruses infecting the same cell or with multiple pathogens inside the same person. For example, a liver cell can be infected by both hepatitis B and hepatitis D.
How common is it? The exact rate is not known, but coinfection is thought to be fairly common and can be more common than a single infection. Infections with parasitic worms (helminths) also affect hundreds of millions of people worldwide.
Why it matters: pathogens inside one person can interact in ways that change disease outcomes. These interactions can be negative (the illness gets worse) or positive (one pathogen helps another spread or survive). Sometimes one organism suppresses another, a phenomenon called negative interactions. The order in which infections occur and how the immune system responds also influence the result.
Understanding coinfection is complex, and patterns aren’t fully known. Some evidence suggests that shared food sources might play a bigger role in coinfections than the immune system alone.
A globally common example is coinfection of tuberculosis (TB) and HIV; in some places, up to 80% of TB patients are also HIV-positive. Other common contexts include AIDS with opportunistic parasites and Lyme disease occurring with other infections.
Coinfections can affect viral load in the nose or throat. In some cases, having rhinovirus together with other respiratory viruses can lead to lower levels of rhinovirus detected.
How coinfection happens at the cellular level: many viruses reach a cell together in various ways, such as in clusters, inside membrane vesicles, or carried by bacteria. In poliovirus, coinfection can allow viable viruses to form even when single infections would be inactivated. It can also lead to genetic recombination, where two viral genomes exchange material inside the same cell, helping viruses preserve a functional genome for progeny.
This page was last edited on 2 February 2026, at 04:06 (CET).