South African HIV prevention campaigns have saved more than 700,000 people from becoming infected with the disease, a major study has shown.

In a joint statement from Johns Hopkins University (JHU) and the Centre for AIDS Development Research and Evaluation (CADRE), the bodies said the study provided evidence that prevention worked.

It also showed that more investment should be made to continue and strengthen prevention interventions.

The infections averted or delayed in 2005 resulted in huge cost savings, estimated at over US 280 million and showed that 64.2 percent of sexually active South Africans (16.7 million people) were practising some form of HIV prevention behaviour.

"Every dollar allocated to prevention is highly effective," said one  of the study's authors Warren Parker from CADRE.

However mass media needed to be complemented with greater personal communication and especially in geographic areas with higher incidence of HIV, he said.

The study re-analysed the Human Sciences Research Council/Nelson Mandela Foundation 2005 household study data.

The data pertained to prevalence, prevention behaviours and the degree to which people had been exposed to national mass media Aids communication programmes - such as Khomanani, Lovelife, Soul City, Soul Buddyz, Tsha-Tsha, Siyayinqoba and Takalani Sesame Street.

Other major findings of the study were that men (69 percent) were more likely than women (60 percent) to take some action to prevent HIV infection.

It showed that while consistent condom usage remained low, there had been a major generational cultural shift.

Condom use in a first sexual encounter among youth was 49 percent  for men and 43 percent for women. These figures were double that of older groups which recorded 20 percent of men and 12 percent of women.

The gender difference in being faithful with a trusted partner was substantial and "once again" favoured men over women (42 percent against 31 percent).

Youth had the lowest levels of faithfulness. Men and women in this category (aged 15 to 24) had about the same moderate levels of faithfulness to a trusted partner (31 percent of men and 32 percent of women).

The study also showed a strong correlation between alcohol and substance abuse and the number of concurrent partners.

Those who reported drinking four to five alcoholic drinks at a time were significantly less likely to practise HIV prevention and were more likely to have higher numbers of concurrent partners.

"We believe that prevention efforts would have even greater effect with a dedicated focus on partner reduction and perceptions of risk," said the study's co-author from JHU Larry Kincaid.

"They also need to address the effects of alcohol use -- it really is a social lubricant that influences sex and HIV," he said.