AS the world marks World AIDS Day today, Sub-Saharan Africa continues to lag behind as the region most affected by HIV.

Southern Africa remains the area most heavily affected by the epidemic, with Namibia itself featuring among the world's top countries with highest prevalence rankings, with a national prevalence rate of between 15 and 20 per cent.

In its 2009 AIDS Epidemic Update, UNAIDS reports that while Sub-Saharan Africa has made a number of substantial gains in responding to the HIV-AIDS pandemic, several important gaps still need to be filled.

"Heterosexual intercourse remains the primary mode of HIV transmission in Sub-Saharan Africa, with extensive ongoing transmission to newborns and breastfed babies", the Update notes.

Women and girls remain disproportionately affected by HIV, with women accounting for about 60 per cent of estimated HIV infections - a trend that UNAIDS says is not only due to their physiological make-up, but also to "the severe social, legal and economic disadvantages they often confront".

It also highlights the role that the high prevalence of a large age gap between sexual partners may have in young women being disproportionately at risk of HIV infection.

Importantly, in terms of new infections, the Update reports that the mode of transmission is also becoming more varied, "with notable new infections occurring among men who have sex with men, and injecting drug users in some countries".

In this regard it points out the lack of data on these populations, although both groups indicate a higher risk to HIV.

The Update also highlights evidence that points to increased HIV prevalence among sex workers, and the role that they play in heterosexual transmission of HIV in the region. "Sex workers are not only a priority population for HIV prevention programmes in their own right - their clients have long been recognised as a potential epidemiological bridge to other populations," says the report.

While the portion of new infections attributable to sex work may have declined, the report says that the low social status of sex workers "impedes efforts to deliver HIV prevention services to this population".

Gains made in addressing the pandemic can't be ignored.

The Update positively notes, for example, that "the rapid scaling-up of antiretroviral therapy in sub-Saharan Africa is generating considerable public health gains".

It adds that "remarkable strides" have also been made in the region with regards to "expanding access to services to prevent mother-to-child HIV transmission", noting that "in 2008, 45 per cent of HIV-infected pregnant women received antiretroviral drugs to prevent transmission to their newborns, compared with 9 per cent in 2004."

The Update also points out that Sub-Saharan Africa has made some significant gains in utilising HIV testing services, and the synthesis of epidemiological and programmatic data.

It also notes the importance of prevention programmes in instilling safer sexual behaviour, and delaying the initiation of sex in some countries; the key role of circumcision in reducing transmission among men; and the fundamental role of HIV testing, counselling and prevention services in antenatal settings.