In the present study, 46 samples from areas in which HIV-1/HIV-2 is endemic, identified in local settings as HIV-2 antibody positive by Genie I/II rapid assay, were analyzed by HIV-1/HIV-2 serological assays (screening and confirmation) and NAAT.
Overall, complete concordance in detecting generic HIV positivity between our screening and confirmatory assays was observed in 44 of the 46 study participants. However, all of these 46 samples were defined as HIV positive by Genie I/II rapid assay, strongly suggesting that nonspecific detection of HIV positivity by Genie I/II assay likely occurred in two of them.
For at least one patient (Table and Table , sample 22), who was on anti-retroviral therapy because of a reduced number of CD4 cells, we could not exclude HIV infection with undetectable serum markers or, alternatively, improper serum storage.
Among all patients, only two (patients 52 and 69) showed discordant results using HIV-2 confirmatory tests.
In sample 52, Inno-LIA detected a clear reactivity to both HIV-1 envelope proteins but also to HIV-2 gp36 (Table ). In addition, NAAT and HIV-2 WB assay could not exclude or confirm HIV-2 infection. The HIV-2 WB assay showed an indeterminate result due to reactivity to only one pol protein (p68) (data not shown). Thus, we could not definitively assess whether patient 52 had single HIV-1 infection (with serum showing cross-reaction on HIV-2 gp36 antigen) or double HIV-1/HIV-2 infection.
Sample 69 was clearly identified as HIV-2 positive by Inno-LIA, with a strong reactivity to gp36 and gp105 antigens, and the result was confirmed by genomic detection of HIV-2, but it was identified as indeterminate by HIV-2 WB. The indeterminate result was due to an uncommon serological pattern characterized by reactivity to only one envelope protein of HIV-2 (gp105/140) but no reactivity to the internal proteins (data not shown). Clearly, in this sample there was an apparent discrepancy between the lack of antibodies to gp36 in HIV-2 WB with respect to the Inno-LIA assay. Overall, the serological pattern of patient 69 suggests that synthetic peptide-based assays may be more sensitive and specific for a correct diagnosis of HIV-2 infection in uncommon samples.
For those samples with double reactivity in the Inno-LIA test, but in which only one or neither genome was detected (21 out of 31), identification of true double infections in this group may be hampered by cross-reactivity between HIV-1 and HIV-2 (1
). Consequently, a more complex diagnostic strategy which includes other discriminatory assays or new specific discriminatory assays should be carried out to ensure appropriate diagnosis of these cases. Among the double infections detected by Inno-LIA, sample number 54 showed strong reactivity to both HIV-2 envelope proteins but to only one of the two HIV-1 envelope antigens (Table , sample 54). Results from genomic and WB assays indicated a clear HIV-2 but not HIV-1 infection (the negative HIV-1 NAAT result was not due to anti-retroviral therapy; see Table ). These findings suggest that this patient was infected by HIV-2 and showed antibodies cross-reacting on HIV-1 gp41 antigen.
Cross-reactivity with the immunodominant regions of HIV-1 envelope proteins was previously reported for HIV-2 subtype B, which is common in Mali and Ivory Coast (9
). This may have implication for the correct diagnosis of HIV-2 in areas in which the virus is endemic and where adequate confirmation tools may not be used (3
). Our results indicate that five patients with single HIV-2 infection would have been misdiagnosed as HIV-1 positive if the HIV-1 WB confirmatory assay had been improperly used. Interestingly, sequence analysis showed that one of these patients was infected with HIV-2 subtype A2, suggesting the need for studies to clarify the impact of HIV-2 genotype variability on accuracy of serological diagnosis.
The issue of “migration and health” is a main health theme in developed countries. Improved surveillance in migrant populations is recommended, particularly to control the HIV epidemic and ensure appropriate therapy. The study of HIV-2 circulation in areas in which the virus is not endemic should be a small but significant part of surveillance programs, at least for countries, like Italy, with increasing numbers of migrants from Africa. To date, a single study, performed in Northern Italy, reported a prevalence of 10.2% for HIV-2 infection in a small population of HIV-infected patients from West Africa, suggesting the need for more extensive studies (7
). On this basis, a concerted effort to improve the accuracy of HIV-2 diagnosis as well as standardization of an international HIV-2 quantitative PCR assay is needed.