Background:  HIV-1 and HIV-2 are highly prevalent in Guinea Bissau; but, while the prevalence of HIV-1 is increasing, HIV-2 is reported to decline. The aim of our study is to analyze the correlates of risk of presenting HIV-1 or HIV-2 infection in a large population of pregnant women living in Bissau and surroundings.

Methods:  From January 2002 to June 2006 the pregnant women attending 10 antenatal clinics in Bissau were consecutively counselled and tested for HIV-1/HIV-2. HIV testing was performed with 2 rapid tests and enzyme-linked immunosorbent assay (ELISA) as confirmation assay. The analyses of trends during the study period (2002 to 2006) for seropositivity was performed by means of Cochran-Armitage test for trend. Differences in HIV prevalence between categorical variables were tested by Pearson χ² statistic. Multivariable logistic regression models were used to determine which factors were associated with HIV seropositivity,

Results:  Of 27,166 pregnant women consecutively attending the antenatal clinics during the study period, a total of 23,869 accepted testing. The prevalence of HIV-2 decreased from 3.0% in 2002 to 2.0% in 2006 (p = 0.0063 ), while the prevalence of HIV-1 were 5.3% and 6.3%, respectively; co-infection remained low and stable (0.6 and 0.5%) In multivariate analysis, the correlates of risk of being HIV-1⁺ were:  older age, profession (working women at higher risk than housewives), the number of sexual partners, the number of previous pregnancies, HIV-2 infection, and belonging to the Beafada and Mandinga ethnic groups, whereas Bijagos and Papel resulted at decreased risk. The correlates of risk of HIV-2 infection were:  older age, profession (housewives at higher risk than the others), number of sexual partners and of previous pregnancies, HIV-1 infection, and belonging to the Beafada group. The correlates of risk of co-infection in the multivariate analysis were:  older age, profession, number of partners, and number of pregnancies.

Conclusions:  Sexual exposure is involved in increasing the risk of both HIV-1 and HIV-2 infection, but the different trends of the 2 infections suggests a highly different efficiency of sexual transmission. The co-infection remains restricted to a minority of cases, suggesting the existence of 2 clearly separate epidemics with limited overlapping; HIV-2 is declining, possibly as a consequence of the reduction of the effect of parenteral risk factors.