What is dual infection, coinfection, superinfection?
Dual infection is when a person is infected with two or more strains of HIV. That person may have acquired both strains simultaneously from a dually infected partner or from multiple partners. A different strain of the virus is one that can be genetically distinguished from the first in a “family,” or phylogenetic tree. Acquisition of HIV strains from multiple partners is often called coinfection if all the strains were acquired prior to your seroconversion, that is, very early before any HIV infection is recognized. Acquisition of different HIV strains from multiple partners is called superinfection if the second virus is acquired after seroconversion. By the way, superinfection and reinfection mean the same thing.
Why does superinfection matter?
Superinfection is a concern because it may be a way for you to acquire drug resistance, and it may lead to more rapid disease progression. People who are HIV-positive and have HIV-positive partners often ask about superinfection. Public health officials need more information, though, in order to craft messages that help explain the risks of unprotected sex among HIV-positive persons, without creating undue anxiety that could undermine rewarding relationships and disclosure of HIV status with prospective new partners. Research on when superinfection may or may not occur could also identify types of immune responses that may protect against infection. This could guide the development of HIV vaccines.
Does superinfection really occur?
Many scientists believe that superinfection can occur. Research in monkeys has indicated that superinfection with viruses like HIV is possible. Scientific literature has so far examined 16 people with SEDI (apparent superinfection), including injection drug users in Asia, women in Africa, and men in Europe and the U.S. Laboratory analysis in some of these reports suggested that the second virus that appeared in these individuals was not present earlier, which suggests superinfection. The sensitivity of these laboratory assays is limited, though, and source partners have not been identified, so there is no way to know for sure when the second virus was acquired.
Who is at highest risk?
Ninety-five percent of apparent superinfection cases have occurred during the first three years of infection. Studies have found evidence of superinfection in 2 to 5 percent of persons in the first year of infection. Intermittent treatment in acute cases or for those just diagnosed may prolong their susceptibility to superinfection.
In contrast, studies of those with longer-term infection have found no evidence of superinfection. One study found no cases after a combined 1,072 years’ worth of observation of its participants. Another found none after 215 person-years of observation among intravenous drug users. A third found none after 233 person-years and 20,859 exposures through unprotected sex.
It is possible that having a very low viral load in your blood makes you more susceptible to superinfection. Low viral load can occur during combination antiretroviral therapy or in “healthy nonprogressors.” Antiviral immune responses and viral interference is lower for these people, so superinfection may occur more frequently. More research is needed to know for sure.