of 2004. The urban curve needs to be adjusted downwards by 40% to account for the bias in urban surveillance sites compared to the entire urban population. The rural curve needs to be adjusted downwards by only 15%. In making this adjustment we assume that the ANC data represent the trend in prevalence and the national survey best represents the level. When these curves are adjusted to match the national population survey of 2004 and weighted by the adult urban and rural populations they suggest that national prevalence among all adults 15–49 in Botswana peaked at about 26% in 2001 and has since declined slightly to 25.7% (24.8%–26.7%) by 2007. This implies that 280,000 adults 15–49 are currently infected, 47% in urban areas and 53% in rural areas. While the national survey in 2004 found that the peak ages for prevalence were 30–34 for both men and women, high levels of prevalence persist up to ages 70– 74. When adult infections over the age of 49 are included the total number of adults infected with HIV is estimated to be about 310,000 (299,000–325,000). Adult HIV Incidence The prevalence trend combined with the pattern of progression from new infection to AIDS death indicates that the annual number of new adult infections peaked at around 33,000 in 1995 and declined to about 20,000 by 2002 and is currently around 18,000 (12,000–26,000). Incidence among those 15–49 is declining, from 3.5% in 2000 to 2.4% in 2007. While the overall population growth rate in Botswana has declined to about 1.7% today, the annual growth rate among all adults is still 2.4%. Therefore, the overall absolute number of new infections each year is approximately constant. Adult AIDS deaths and the effects of ART The annual number of adult AIDS deaths rose steadily during the 1980s and 1990s to a peak of nearly 16,000 in 2003. Without any ART program adult AIDS deaths would have continued increasing to nearly 23,000 in 2007. However, Botswana has implemented a vigorous treatment program that has expanded the number of adults receiving ART from 932 in 2000 to 85,497 by the end of 2007, about 83% of need [11]. As a result the estimated number of adult AIDS deaths has dropped to 7400 (5000–11,000) in 2007 (Figure 2b). The provision of ART has averted an estimated 53,000 deaths from 2000 to 2007. If these deaths had not been averted by ART then AIDS deaths would have exceeded new infections and adult HIV prevalence would have been much Figure 2. Annual number of new child infections (Figure 2a) and adult deaths (Figure 2b), 1980–2007. doi:10.1371/journal.pone.0003729.g002 HIV in Botswana lower. We estimate that prevalence would have declined to 22.7% in 2007, three percentage points lower than the actual estimate. Those currently receiving ART will continue to need it for many years to come. In addition, about 23,000 adults newly progress to need for ART each year. As a result the need for ART is expected to increase by almost 60% from 120,000 (101,000– 136,000) in 2007 to about 190,000 by 2016 if the high levels of coverage are maintained. This has important cost and sustain- ability implications for the programme. Child infections and the effects of PMTCT The high levels of HIV infection in adults mean that many children are exposed to the risk of acquiring infection from their mothers. The estimated number of new infections among children peaked at around 4600 in 1999. PMTCT services were introduced in 2002 and coverage expanded rapidly. By 2007 91% of HIV- positive pregnant women received antiretrovirals to reduce the risk of mother-to-child transmission [12]. More than half of these women receive a combination of single dose Nevirapine and AZT. The program carefully tracks women attending antenatal care and women giving birth recording HIV status and for those HIV+ women it reports the number of women evaluated for ART, eligible for ART, already on ART, and use of AZT, Nevirapine and co- trimoxazole. Since early 2007 the program has tracked outcomes for children born to HIV-positive mothers by using dried blood spots and PCR tests on all children born to HIV+ mothers. The results to date indicate that the program has reduced the average mother-to- child transmission rate to just 3.7% by 2007 [12]. Using this figure we estimate that the annual number of new child infections is now about 890 (810–980) (Figure 2a). The expansion of the PMTCT program has averted 10,000 child infections from 2002 to 2007. HIV-positive children have benefited from an expansion of treatment programs. By the end of 2007 7,400 children were receiving ART, nearly all those estimated to be in need, and almost 10,000 were receiving co-trimoxazole. As a result child AIDS deaths have been reduced from about 3,000 in 2001 to 790 (600–1020) in 2007. Nearly 11,000 child deaths have been averted by the combined effects of PMTCT, child treatment and adult ART. Orphans As a result of adult AIDS deaths a significant proportion of children have lost one or both parents. We estimate that there were 130,000 (110,000–150,000) orphans in 2007, about 16% of all children under the age of 18. Three-quarters of these orphans are due to AIDS. One-third of households caring for orphans are receiving external support [12]. The success of the adult ART program has reduced the number of new orphans each year by 40%, from 20,000 in 2002 to 12,000 in 2007. Discussion Botswana has an HIV surveillance system and a national HIV survey that provide the basis for estimates of the extent of the HIV epidemic and its dynamics. These data indicate that prevalence is currently declining slightly in urban areas and stable in rural areas. The estimates produced from these data indicate that the number of new infections rose rapidly during the early 1990s, peaking in the mid-1990s before falling to a stable level of about 18,000 new infections per year today. The number of AIDS deaths started to grow rapidly about 10 years later than the rise in new infections, peaking just before the expansion of ART. The successful expansion of the ART program has increased coverage to over 80% of those in need of treatment. This expansion has had significant benefits, reducing the annual PLoS ONE | www.plosone.org 3 November 2008 | Volume 3 | Issue 11 | e3729