Coinfection

Coinfection is the simultaneous infection of a host by more than one pathogen species. In virology the term also covers infection of a single cell by two or more virus particles, for example liver cells infected with both hepatitis B virus and hepatitis D virus. The global prevalence among humans is unknown, but coinfection is thought to be commonplace and sometimes more common than single infection; helminth coinfection alone affects around 800 million people. It matters for health because the pathogens can interact inside the host, and the net effect on human health is thought to be negative. Positive interactions enhance transmission and progression, known as syndemism, while negative ones include microbial interference, such as Pseudomonas aeruginosa suppressing Staphylococcus aureus colonies. Outcomes depend on the order of exposure and the host response. A globally common example is tuberculosis with HIV, where in some countries up to 80 percent of tuberculosis patients are also HIV-positive.