Background:  HIV-1 is subdivided into groups M, N, and O. Dual infections by both strains M and O are rare and no cases of superinfection by 1 group in a patient previously infected by another group have so far been described. We observed a patient living in France and previously infected by a HIV-1 group O variant superinfected by a HIV-1 group M CFR02_AG recombinant strain.

Methods:  An HIV-infected Cameroon woman (AMF) had been living in western France since September 2002 with her new sexual partner, a French sailor infected by HIV-1 group M subtype CRF02_AG. AMF conceived in December 2002. During the monitoring before and during her pregnancy, a serological and molecular follow up was performed using specific group M and group O peptide-based ELISA and specific group M and group O viral load assays [(Cobas Amplicor Monitor v1.5 assay (Roche); and in-house group O-specific real-time polymerase chain reaction (PCR) based on LightCycler (Roche)]. LTR, Gag, Pol and Env proviral DNA was amplified, followed by sequencing and phylogenetic analysis.

Results:  In October 2002, HIV-1 group O infection in AMF was first suggested by undetectable viral load in the HIV-1 group M-specific Cobas Amplicor. The group O infection was confirmed using a group O peptide-based ELISA and by sequencing. During a 19 months follow up, plasma HIV-1 group O RNA ranged between 3.4 and 5 log. At M3, a weak reactivity was observed in Cobas Amplicor with a viral load at 3.2 Log suggesting a HIV-1 group M superinfection. Serial group M and group O specific serologic tests confirmed the presence of anti-V3 group O antibodies and the increasing reactivity against anti-V3 group M antibodies. Anti-V3 group M antibodies were detected as early as month 7 with a significant increase in reactivity at M19. Molecular findings on the LTR, Gag, Pol, and Env regions were positive only for group O before the pregnancy but for both group O and M fragments at delivery. Sequencing of the Env fragment confirmed that AMF was infected by group M CRF02_AG phylogenetically related to her partner's viral Env region. At this date, her partner was not superinfected by HIV-1 group O.

Conclusion:  Superinfection, which could be clearly shown in our patient because the large antigenic and molecular divergence between groups M and O, is likely to be a frequent phenomenon. The total lack of cross-protection between HIV types, groups, and subtypes is striking and underlines the need for close molecular  epidemiological monitoring worldwide.

Keywords: HIV-1 SUPERINFECTION; HIV-1 GROUP O; HIV DIVERSITY