Coinfected refers to a situation where two or more infections occur simultaneously in a single host. Other words that can be used interchangeably with coinfected include concomitantly infected, dually infected, multiply infected, or co-occurring infections. When people are coinfected with two viruses, they are known to be in a state of superinfection. It is possible to be coinfectious, that is, able to transmit multiple infections to others. In medical terms, co-infections are quite common. The concept of coinfection is mainly applied in microbiology to describe infections in which two or more microorganisms such as fungi, bacteria, or viruses invade a host together. Several diseases, including HIV, hepatitis C, and tuberculosis, can commonly present as coinfections.