HIV-1 plasma viral load at different clinical stages. HIV infection is characterized by an acute phase with a high viral load, which decreases as specific immunity develops (solid line). After seroconversion (SC), the chronic phase of the infection starts, lasting several years. The chronic phase of the infection is traditionally followed by the AIDS phase, but is now increasingly replaced by the start of antiretroviral therapy (ART) in many parts of the world. An HIV-1 dual infection during the acute phase is called a co-infection, after seroconversion it is referred to as a superinfection. HIV-1 superinfections often result in an increase, sometimes temporary, of the viral load (dotted line) and an earlier start of therapy. HIV-1 superinfections in most cases are found close to the acute infection, and only rarely occur later than a few years after primary infection.