Global Epidemiology of HIV-AIDS

Infect Dis Clin N Am

21 (2007) 1–17

Global Epidemiology of HIV-AIDS

Salim S. Abdool Karim, MBChB, PhDa,b,*,Quarraisha Abdool Karim, PhDa,b,

Eleanor Gouws, MSc, MPHc, Cheryl Baxter, MSca

aCentre for the AIDS Program of Research in South Africa–CAPRISA, Doris Duke Medical

Research Institute (2nd Floor), Nelson R. Mandela School of Medicine,

University of KwaZulu-Natal, Private Bag X7, Congella, 4013 Durban, South AfricabMailman School of Public Health, Department of Epidemiology, Columbia University,

722 West 168th Street, New York, NY 10032, USAcDepartment of Policy, Evidence and Partnerships, UNAIDS, Geneva, Switzerland

HIV, the cause of AIDS, has in the 25 years since its discovery spreadrapidly to every region in the world [1]. To date, more than 65 million peoplehave been infected with HIV and about 25 million people have died fromAIDS [1]. In the current decade of the epidemic, there has been a substantialincrease in HIV infection in women, and about 40% of all new infectionsamong adults occurred in young people 15 to 24 years of age. At the endof 2006 [2], the Joint United Nations Programme on HIV/AIDS (UNAIDS)estimated that there were a total of 39.5 million (34.1–47.1 million) adultsand children living with HIV. In 2006, a total of 4.3 million (3.6–6.6 million)new infections occurred and 2.9 million (2.5–3.5 million) people died fromAIDS.

Modes of HIV transmission

Globally, sexual transmission is the dominant mode of HIV spread, witha concomitant epidemic in infants born to HIV-infected mothers. HIV isalso spread through contaminated blood, either through sharing of needles

Support was received from CAPRISA, which forms part of the Comprehensive

International Program of Research on AIDS funded by the National Institute of Allergy and

Infectious Disease, National Institutes of Health, and the US Department of Health and

Human Services (grant No. U19 AI51794).

* Corresponding author. CAPRISA–Doris Duke Medical Research Institute (2nd Floor),

Nelson R. Mandela School of Medicine, University of KwaZulu-Natal, Private Bag X7,

Congella, 4013 Durban, South Africa.

E-mail address: [email protected] (S.S. Abdool Karim).

0891-5520/07/$ - see front matter � 2007 Elsevier Inc. All rights reserved.

doi:10.1016/j.idc.2007.01.010 id.theclinics.com

mailto:[email protected]

2 ABDOOL KARIM et al

and syringes used for illicit intravenous drugs, transfusion of blood and bloodproducts, or contaminated needles and equipment in medical care settings.

It is estimated that sexual transmission (heterosexual and sex betweenmen) accounts for about 85% of the global HIV burden. The presence ofHIV infection can be assessed by laboratory assays, which include detectionof HIV antibodies (HIV ELISA), constituent viral proteins (p24 ELISA),and HIV genes (polymerase chain reaction). Either singly or in combination,these accurate assays facilitate the detailed study of the epidemiology ofasymptomatic HIV infection.

The differential spread of HIV around the world is partially explained bythe fact that not all modes of HIV transmission confer the same risk. Studieshave shown that the risk of male-to-female transmission of HIV is higherthan the risk of female-to-male transmission [3,4]. A study in the early1990s conservatively estimated the risk of acquiring HIV through peno-vag-inal sex to be 3 per 10,000 contacts for the male partner and 20 per 10,000contacts for the female partner [3]. Anal sex among homosexual men hasbeen associated with a risk per sexual contact of between 50 to 300 per10,000 receptive anal exposures [5]. It is recognized that many uncertaintiesexist in estimates of transmission probability, and both behavioral and bio-logic factors can influence the infectiousness of HIV-infected individuals andthe susceptibility of HIV-negative individuals. The risk of HIV transmissionvaries by HIV viral load, stage of HIV infection, HIV treatment status,circumcision status, presence of sexually transmitted infections (STIs), andsexual behavior and sociodemographic factors [5–10]. For example, HIV in-fectivity has been shown to be significantly higher in the presence of genitalulcerative disease [9], whereas female-to-male infectivity of HIV is signifi-cantly lower among men who have been circumcised compared with uncir-cumcised men [6]. In a study in Uganda, transmission probabilities amongheterosexual HIV-1–discordant couples increased from 1 per 10,000 per sex-ual act at viral loads of !1700 copies/mL to 23 per 10,000 per act atR38,500 copies/mL [9]. A literature review of the risk of HIV transmissionfor parenteral exposure and blood transfusion showed that estimates varybetween 6.3 per 1000 and 24 per 1000 (median, 8 per 1000) for intravenousdrug injection; 0 to 4.6 per 1000 (estimate weighted by precision, 2 per 1000)for accidental percutaneous injury; and 89 to 96 per 100 (estimate weightedby precision, 92.5 per 100) for contaminated blood transfusion [11].

Sexual transmission

Lifelong mutual monogamy is protective. Serial monogamy, where thereare multiple sequential individual short-lived monogamous partnerships, isassociated with an increased risk of HIV, but not to the same extent asthe substantial increase in risk of transmission emanating from multipleconcurrent sexual partnerships [12]. Reduction in the number of concurrentsexual partnerships and the use of condoms are key factors in HIV

3GLOBAL EPIDEMIOLOGY OF HIV-AIDS

prevention messages, widely promoted as part of ‘‘ABC’’ campaigns pro-moting Abstinence, Be faithful, and Condomise. Knowledge of HIV status,through voluntary counseling and testing, has been shown substantially toreduce risky sexual behaviors [13]. Stigma, which is a common experienceof those infected and affected by HIV, is a major obstacle to HIV testingand acknowledgment of individual risk of infection [14].

The efficiency of HIV transmission through sex is influenced by severalfactors, including the use of condoms, presence of other STIs, and viralload. Consistent and correct condom use is highly protective against HIVtransmission. High viral load during acute HIV infection [10,15] and ad-vancing HIV disease [15,16] significantly increase the risk of transmission.Coinfections with other STIs [17–19], particularly those that cause genitalulcers, also increase the risk of transmission. The presence of STIs hasbeen particularly important in the rapid transmission of HIV among sexworkers [20].

The future course of the HIV pandemic will be substantially influencedby the sexual behavior and risk of HIV transmission among young people.In 2005, it was estimated that 40% of all new adult infections occurred inpeople between 15 and 24 years of age [21]. One of the goals of the 2001Declaration of Commitment of the United Nations General Assembly Spe-cial Session on HIV/AIDS is to reduce HIV prevalence in young people by25% by 2010 [21]. The effect of HIV on children has been devastating [22]. Itis estimated that 2.3 million (1.7–3.5 million) children younger than 14 yearswere living with HIV in 2005, whereas 15.2 million (13.3–17 million) wereorphaned as a result of AIDS [21]. About 87% (2 million) of all children in-fected with HIV and 79% of all AIDS orphans (12 million) live in sub-Saharan Africa. Children not only suffer from being infected themselves,but also suffer the psychologic trauma of having to care for sick and dyingparents, while having to provide for other family members. In addition, or-phaned children, among whom less than 10% are receiving public supportand services, often live in severe poverty and are vulnerable to abuse [22],thereby increasing their risk of HIV infection.

Mother-to-child transmission

HIV is transmitted in utero, during the process of childbirth and throughbreast-feeding. Most transmission from mother-to-child occurs duringchildbirth where the mother’s infected blood in the birth canal infects thebaby. Breast-feeding, particularly in poor countries, can account for onethird to one half of all mother-to-child transmissions [23]. In 2005, only9% of pregnant women in low- and middle-income countries were offeredservices to prevent transmission to their newborns [24]. As availability ofantiretroviral therapy to reduce mother-to-child transmission during child-birth increases, breast-feeding is assuming a proportionately greater roleas a source of HIV spread to newborn babies [23].


Blood transfusion

Notable progress has been made worldwide in improving the safety of na-tional blood supplies, and nearly all countries routinely screen blood forHIV antibodies. Some national blood screening efforts are impeded by inad-equate quality assurance mechanisms, poor staff training, and suboptimallaboratory procedures, however, which can cast doubt on the reliability oftest results [21,25]. The ‘‘window period,’’ when HIV antibody tests are neg-ative but the blood is infectious, is a major concern of blood transfusion ser-vices. The use of antigen assays, polymerase chain reaction to detect viralgenes, and quarantine of first blood donations until subsequent donationsprove to be uninfected are some of the strategies used to reduce the riskof transfusing infected blood [25].

Contaminated injection equipment

Harm reduction programs that provide clean needles and syringes haveproved effective in reducing the risk of HIV transmission among injectiondrug users, without contributing to an increase in drug use [26]. In manyareas of the world, however, this continues to be an important mode oftransmission because of lack of political will and commitment to make nee-dle exchange or methadone maintenance programs available. Transmissionthrough the reuse of needles and syringes in medical settings is a particularconcern in poor countries, where universal precautions have not been ade-quately implemented [21].

Geographic distribution of HIV infection

There is substantial variability in the geographic distribution of HIV in-fection (Fig. 1). In 2005, about 6% of the adult population living in sub-Sa-haran Africa were infected with HIV in contrast to !0.5% in East Asia,North Africa and the Middle East, West and Central Europe, and Oceania[21].

Sub-Saharan Africa is severely affected by HIV. Currently, it accountsfor 63% (24.5 million [21.6–27.4 million]) of global infections (see Fig. 1)[21]. It is estimated that 2.7 million (2.3–3.1 million) people in this regionbecame newly infected in 2005, whereas 2 million (1.7–2.3 million) diedfrom AIDS in this period. Most infections in this region occur through het-erosexual contact, where women are disproportionately affected. In this re-gion, the ratio of women to men living with HIV is 3:2 [21]. Although HIVprevalence in sub-Saharan Africa overall seems to be stabilizing [21], thereare still a few countries in this region, mainly in Southern Africa, wherethe epidemic is continuing to rise.

Southern Africa is the most affected region in the global pandemic; it isestimated that about 43% of all HIV-infected children globally and about


52% of all HIV-infected women live in this subregion despite it being hometo less than 1% of the world’s population. Several countries in East andSouthern Africa have shown a decline in prevalence in recent years, includ-ing Kenya, Zimbabwe and urban areas in Rwanda [21,27–29]. In contrast,whereas Uganda has for years been an excellent role-model for successfullyimpacting the HIV epidemic, data demonstrate that prevalence and inci-dence have no longer been falling in recent years [30].

HIV prevalence in the Middle East and North Africa is low and has notexceeded national HIV prevalence rates of 0.2%, with the exception of Su-dan, where national prevalence in 2005 was estimated at 1.6% [21]. A totalof 440,000 (250,000–720,000) people were living with HIV in this region in2005. The main modes of transmission in this region are unprotected sexualcontact (including commercial sex and sex between men) and injecting drugsusing contaminated equipment. In some countries in North Africa and theMiddle East, a significant number of infections still result from contami-nated blood products, blood transfusions, or lack of infection-control mea-sures in health care settings, although the extent of this has decreasedsignificantly over the last 10 years [31].

The HIV epidemics in Latin America and the Caribbean are associatedmainly with unsafe sex (both heterosexual and men who have sex withmen [MSM]) and use of contaminated drug-injecting equipment, especiallyamong the poor and unemployed. In Latin America, an estimated 1.6 mil-lion (1.2–2.4 million) people were living with HIV in 2005. In most LatinAmerican countries, HIV prevalence is highest among MSM. A total of

North America

1.3 million

[770 000 – 2.1 million]HSex, MSM, IDU

Eastern Europe & Central Asia

1.5 million

[1.0 –2.3 million]IDU

Caribbean

330 000

[240 000 – 420 000]HSex, MSM

Latin America

1.6 million

[1.2 – 2.4 million]HSex, MSM, IDU

Oceania

78 000

[48 000 – 170 000]MSM

East Asia

680 000

[420 000 – 1.1 million]HSex, IDU, MSM

South & South-East Asia

7.6 million

[5.1 – 11.7 million]HSex, IDU

Western and Central Europe

720 000

[550 000 – 950 000]

North Africa & Middle East

440 000

[250 000 – 720 000]HSex, IDU

Sub-Saharan Africa

24.5 million

[21.6 – 27.4 million]HSex

Adult prevalence rate

15.0%-34.0%5.0% - <15.0%

1.0% - <5.0%0.5% - <1.0%

0.1% - <0.5%<0.1%

A global view of HIV infection38.6 million people [33.4-46.0 million] living with HIV, 2005

Fig. 1. Global distribution of people (adults and children) living with HIV in 2005. Major

modes of HIV transmission are abbreviated as follows: HSex, heterosexual; IDU, injection

drug use; MSM, men who have sex with men. (Adapted from Joint United Nations Programme

on HIV/AIDS. 2006 report of the global AIDS epidemic. Geneva: UNAIDS; 2006. Available

at: http://www.unaids.org/en/HIV_data/2006GlobalReport/. Accessed April 26, 2007; with

permission.)

http://www.unaids.org/en/HIV_data/2006GlobalReport/


330,000 (240,000–420,000) people were living with HIV in the Caribbean,with AIDS the leading cause of death among adults in 2005 [31], havingclaimed an estimated 27,000 (19,000–36,000) lives. Although a significantproportion of HIV infections in the Caribbean can be attributed to MSM,it is likely to be underestimated because of sociocultural stigma, whichresults in underreporting.

In North America, Western Europe, and Central Europe, HIV preva-lence has remained below 1% and AIDS mortality has been low becauseof the wide availability of antiretroviral therapy. A total of 2 million (1.4–2.9 million) people infected with HIV live in these regions (see Fig. 1), ofwhom about 1.2 million live in the United States. A total of 65,000(52,000–98,000) people were newly infected in these regions in 2005 [21]. Un-safe sexual practices between men and the use of contaminated drug-inject-ing equipment are the most important routes of transmission of HIV inthese regions. In recent years, however, there has been an increase in hetero-sexual transmission and more women and members of minority ethnicgroups have become infected through unsafe sex.

Epidemic patterns have also been changing in Eastern Europe and Cen-tral Asia in recent years, where an increasing number of women are beinginfected, many of whom acquire HIV infection from their male partnerswho became infected through injecting drugs using shared, contaminated in-jecting equipment. The epidemics in this region are growing. The total num-ber of people living with HIV increased by about 36% from 2003 to 2005[21]. UNAIDS estimates that, of the 1.5 million (1–2.3 million) people livingwith HIV, 220,000 (150,000–650,000) were newly infected with the virus in2005 [21]. The Russian Federation and Ukraine account for most infectionsin this region (an estimated 940,000 people in the Russian Federation and410,000 people in Ukraine were living with HIV in 2005), most infectedthrough injecting drugs using contaminated equipment.

In Asia, it is estimated that there were 8.3 million (5.7–12.5 million) peo-ple living with HIV at the end of 2005; 930,000 (620,000–2.4 million) be-came newly infected with HIV and 600,000 (400,000–850,000) died fromAIDS during 2005 [21]. About 69% of all people infected with HIV inthis region live in India. With a total population of over 1 billion people,however, the adult prevalence in India is still below 1% (estimated at0.91%) [32], with variation between different states. In India, HIV transmis-sion is primarily heterosexual, with female sex workers and their clients be-ing the main drivers of HIV transmission. HIV is starting to spread in somestates in India, however, to the regular sexual partners of clients of sexworkers [33].

Thailand provides an example of the dynamic nature of the epidemic ata country level. The main routes of transmission in the late 1980s and early1990s were through the use of nonsterile equipment in injecting drug usersand through sex work from where it spread in the 1990s to the clients andpartners of clients of sex workers. Although the 100% condom use policy


in brothels made a major impact on preventing sexual spread of HIV to thegeneral population, it’s more conservative policy on needle exchange andmethadone treatment has enabled HIV to spread rapidly to injecting drugusers who are potentially an important bridge to the general population.In 2005, it was estimated that about 43% of all new infections in Thailandoccurred in the low-risk heterosexual population, whereas 21% of new in-fections occurred among MSM [8], and 7% among IDUs and their partners.

In East Asia (including China, Japan, Mongolia, Republic of Korea, andDemocratic People’s Republic of Korea), adult prevalence remains low andhas not yet reached 0.1%. In most of the rest of the countries in Asia, HIVprevalence remains low; only Cambodia, Thailand, and Myanmar had adultHIV prevalence rates above 1% (1.6%, 1.4%, and 1.3%, respectively) in2005 [21].

Of 78,000 (48,000–170,000) people infected with HIV in Oceania, it isestimated that 77% (60,000 [32,000–140,000]) are living in Papua NewGuinea, where the epidemic started recently, but is growing rapidly. The num-ber of people living with HIV in Papua New Guinea has increased by about30% per year since 1997 [21], reaching an adult prevalence of 1.8% in 2005,with the main mode of transmission through unsafe sex. HIV prevalence inother countries in this region (including Australia, New Zealand, and Fiji)has remained low at about 0.1% [21] and is mainly concentrated in MSM.

Genetic subtypes of HIV

HIV-1 is the dominant virus in the pandemic. HIV-2 is restricted mainlyto West Africa [34]. Numerous HIV-1 subtypes and circulating recombinantforms [35] make up the complex mosaic of the global HIV-1 pandemic. Thehigh viral replication rate, low fidelity of reverse transcription, and the abil-ity to recombine has led to HIV’s genetic diversity, which has been charac-terized as subtypes (or clades). A recent analysis of 23,874 HIV samplesfrom 70 countries shows that in terms of viral diversity, subtype C virusesdominate and accounted for half of all HIV-1 infections worldwide in2004, whereas subtypes A, B, D, and G accounted for 12%, 10%, 3%,and 6%, respectively [36]. Circulating recombinant forms were responsiblefor 18% of infections worldwide. Subtype C is predominant in Africa andAsia, whereas subtype B is the commonest subtype in Europe and the Amer-icas. Although uncommon, there are reports of dual infection, which indi-cates that individuals can become infected with more than one subtype ofHIV, usually at different time points [37,38].

Epidemiologic typology: case studies of low, concentrated, and generalized

HIV epidemics

UNAIDS has classified the differing stages of the epidemic as either gen-eralized, concentrated, or low level, depending on the prevalence and mode


of transmission. In settings where the adult HIV prevalence is firmly estab-lished in the general population and transmission is mostly heterosexual, ep-idemics are classified as generalized, whereas concentrated and low-levelepidemics are restricted to regions where HIV is concentrated in groupswith behaviors that expose them to a high risk of HIV infection (Table 1).These categorizations have been developed to assist countries in designingtheir surveillance systems. However, for prevention planning, an additionalanalysis of the local epidemic is necessary to identify which exposures or be-haviors lead to important numbers of new infections [8].

Case study of a low-level epidemic: the Philippines

In the early 1990s, the Philippines government responded aggressively tothe threat of an emerging HIV epidemic by instituting an action plan thatemphasized the response of the local government agencies, involvementand support of nongovernmental organizations, incorporation of HIV-AIDS education into the school curriculum, and laws forbidding discrimina-tion against people belonging to high-risk groups or people living with HIV[39]. This early aggressive response has meant that HIV did not result ina widespread epidemic in the Philippines.

The first AIDS case was detected in the Philippines in 1984, but nationaladult HIV prevalence has remained below 0.1%. In 2005 an estimated12,000 (7300–20,000) adults and children were living with HIV [21]. Ratesin all the usual high-risk groups (sex workers, MSM, STI clients, and inject-ing drug users) have remained low [40]. A survey among female sex workersshows that HIV prevalence has remained below 1% (0.1%, 0.02%, and0.16% in 2002, 2003, and 2005, respectively). Among injecting drug usersin Cebu City in 2005, the HIV prevalence is estimated at 1% [40].

The low level of HIV in the Philippines may be caused by the high pro-portion of monogamous relationships, relatively low number of full-time sexworkers, low number of sex worker clients per night, low rates of anal sex,low prevalence of ulcerative STIs, low proportion of injectors among drugusers, high proportion of male circumcision, the early multisectoral responseto the epidemic, and the presence of social hygiene clinics for sex workerswho also have good access to HIV prevention services [41].

This could change, however, given infrequent use of condoms duringpaid sex, high levels of nonulcerative STIs in some population groups,and high rates of needle-sharing among drug injectors in some areas (eg,77% in Cebu City) [39,41]. The Philippines, which has successfully keptHIV rates low, are aware of the possibility of an increase in the spread ofHIV if their aggressive approach is not maintained. Vietnam and Indonesia,which are examples of delayed HIV epidemics, where initial control of HIVtransmission was superseded by rapid spread of HIV in high-risk popula-tions, serve as a constant reminder to the Philippines of the importance ofcontinued efforts to keep the epidemic in check [41].

Table 1

Characteristics of

Generalized epide Low-level epidemic

� HIV is firmly e

� Although subpo

to contribute d

HIV, sexual net

sufficient to sus

subpopulations

� HIV prevalence

pregnant wome

ished

ion

% in

IV

omen

� Although HIV infection may have existed

for many years, it has never spread to

significant levels in any subpopulation

� Recorded infection is largely confined to

individuals with higher-risk behavior, such

as sex workers, drug injectors, and men

who have sex with men

� This epidemic state suggests that networks

of risk are rather diffuse (with low levels of

partner exchange or sharing of drug

injecting equipment) or that the virus has

been introduced only very recently

� HIV prevalence has not consistently

exceeded 5% in any defined subpopulation

Adapted from

9GLOBALEPID

EMIO

LOGY

OFHIV

-AID

S

generalized, concentrated, and low-level epidemics

mic Concentrated epidemic

stablished in the general population

pulations at high risk may continue

isproportionately to the spread of

working in the general population is

tain an epidemic independent of

at higher risk for infection

is consistently over 1% among

n

� HIV has spread rapidly in a defined

subpopulation, but is not well-establ

in the general population

� This epidemic state suggests active

networks of risk within a subpopulat

� HIV prevalence is consistently over 5

at least one defined subpopulation; H

prevalence is below 1% in pregnant w

in urban areas

UNAIDS, www.UNAIDS.org.

http://www.UNAIDS.org


Case study of a concentrated epidemic: United States of America

The United States is categorized as having a concentrated epidemic. Sincethe first cases of AIDS, which were reported in 1981 [42], the HIV epidemichas continued to expand and by the end of 2005, about 1.2 million (720,000–2 million) [2] people were living with HIV, an estimated 24% to 27% ofwhom were unaware of their infection and are unaware of their risk forHIV transmission [43]. Nationally, adult HIV prevalence in 2005 was an es-timated 0.6% (0.4%–1%) [21].

In the 1980s, AIDS cases increased rapidly and peaked in 1992 before sta-bilizing in 1998; since then, there have been approximately 40,000 new HIVinfections annually [44]. Although roughly three quarters (74%) of Ameri-cans estimated to be living with HIV are male, women are increasinglyaffected by the epidemic, with the proportion of women with AIDS increas-ing from 15% (1981–1995) to 27% (2001–2004) [45].

MSM remain the most severely affected group, accounting for 45% ofpeople living with HIV in the United States [45]. Individuals infectedthrough high-risk heterosexual contact comprised 27%, and those infectedthrough injection drug use accounted for 22% of the HIV-positive popula-tion in 2003. The proportion of HIV infections and AIDS cases who areMSM has remained stable, whereas the proportion caused by intravenousdrug use decreased by 9.1% from 2001 to 2004 [45].

Since the beginning of the epidemic, community-based activism has beencritical in galvanizing the United States response to the HIV epidemic. TheUnited States Congress responded by providing funds to states, metropoli-tan areas, and local communities to improve the quality and availability ofcare and implement prevention programs. One of the most successful publichealth achievements in HIV prevention in the United States is the dramaticreduction in mother-to-child HIV transmission from approximately 1700per annum during the mid-1990s to about 145 in 2002 [46]. This decline isattributed to multiple interventions, including routine voluntary HIV testingof pregnant women, the use of rapid HIV tests at delivery for women of un-known HIV status, and the use of antiretroviral therapy by HIV-infectedwomen during pregnancy and by infants after birth.

Although considerable progress has been made in reducing the impact ofthe HIV epidemic, certain populations, especially racial and ethnic minori-ties, continue to bear a disproportionate burden of disease. During 1981 to1995, non-Hispanic whites accounted for 47% of all AIDS cases diagnosed,but over time this has decreased and the proportion of cases among AfricanAmericans and Hispanics has increased considerably. Although AfricanAmericans currently make up just over 12% of the United States popula-tion, they account for half of all new HIV cases [44]. African Americanwomen are up to 12 times more likely to be infected with HIV than theirwhite counterparts [47]. In 2003, almost twice as many African Americansdied of AIDS than did whites [44].


A total of 522,723 AIDS-related deaths were reported between 1981 and2004. Survival after diagnosis of AIDS has increased substantially since1996. The proportion of persons living at 2 years after AIDS diagnosiswas 44% for those diagnosed between 1981 and 1992, increasing to 64%for those diagnosed between 1993 and 1995, and 85% if diagnosed between1996 and 2000 [45]. With the introduction of highly active antiretroviraltherapy, the overall progression of HIV infection to AIDS and fromAIDS to death has slowed substantially in the United States [48].

Despite impressive accomplishments in controlling HIV in the UnitedStates, several new challenges have arisen. HIV-AIDS continues to be a sig-nificant cause of illness and death in the United States, and many people areunaware of their status despite the widespread availability of testing services[43]. Additionally, some of the early prevention successes among MSM inthe United States are being reversed because there is reported evidence ofresurgent risk behavior in this group [49]. In the city of Baltimore, for exam-ple, HIV incidence of 8% has been found in MSM in 2005, and 62% of themen testing HIV-positive in that city were unaware that they had beeninfected [43,50].

Case study of a generalized epidemic: South Africa

A total of 5.5 million (4.9–6.1 million) people, of the total population of44 million, are currently estimated to be living with HIV in South Africa[51]. Approximately 18.8 (16.8–20.7) of the adult population of the SouthAfrican population is estimated to be infected with HIV [2]. The epidemicis predominantly caused by heterosexual transmission; in a 15-year periodfrom 1990 to 2005, national HIV seroprevalence among antenatal clinic at-tendees has increased explosively from 0.7% to 30.2% [51,52]. The prov-ince of KwaZulu-Natal is at the most advanced stage of the epidemicand antenatal HIV prevalence has increased from 1.6% in 1990 to39.1% in 2005 (Fig. 2). High rates of STIs, the migrant labor system,high rates of gender-based violence and low rates of circumcision haveall contributed to the large and growing burden of HIV infection in SouthAfrica [53].

HIV prevalence is highest in young women, who are bearing the brunt ofthe HIV epidemic in South Africa. Among 20- to 29-year-old women in a ru-ral South African district, the HIV prevalence grew from 39.5% in 2001 to58.7% in 2004 (CAPRISA, Dr. Quarraisha Abdool Karim, unpublisheddata, 2006).

Not only are young women more severely affected in the South AfricanHIV epidemic, but they acquire their infection at a much earlier age thanmen [53]. These striking gender differences have contributed to rapid growthin the HIV epidemic in South Africa. Although not unique to South Africa,marginalization and discrimination on the basis of race or ethnicity is an-other key factor influencing vulnerability to HIV infection [54].


The South African response to the HIV epidemic was tardy in the 1990sbecause of substantial political changes from apartheid to democracy in1994. Since 2000, the government’s response has been characterized bydenialism and political suspicion of antiretroviral therapy, whereas com-munity-based activism has had a major policy impact, including the provi-sion of free antiretroviral therapy. From August 2003 to March 2006, morethan 200,000 South Africans have initiated antiretroviral therapy in both thepublic and private health care services [55].

Tuberculosis is the most common serious infectious complication associ-ated with HIV infection in South Africa [56]. The increasing HIV infectionrate is compounding the tuberculosis epidemic in South Africa. About64.6% of newly diagnosed cases of pulmonary tuberculosis are coinfectedwith HIV [56]. Approximately 2 million HIV-infected South Africans arecoinfected with tuberculosis, and the incidence of all forms of tuberculosisin South Africa was 509 per 100,000 population in 2002 [56]. Recently, anoutbreak of extensively drug-resistant tuberculosis was described in SouthAfrica; the important feature of this outbreak was that all those testedwere HIV infected and the condition was uniformly rapidly fatal, death oc-curring within a median of 16 days from specimen collection [57].

Tuberculosis incidence rates continue to rise, and with it, the incidence ofmultidrug resistant and extensively drug-resistant tuberculosis, because HIV

< 1%1.0-4.9%5.0-9.9%10.0-14.9%15.0-19.9%20.0-24.9%>25%

HIV Prevalence

1990 1995

2000 2005

Western

Cape

Eastern

Cape

Northern

Cape

North

West

Free

State

Mpumalanga

Northern

ProvinceGauteng

KwaZulu

Natal

Fig. 2. HIV prevalence in pregnant women in South Africa’s nine provinces, based on the

South African Department of Health Antenatal HIV surveys.


transmission continues to rise relentlessly in South Africa with an estimated1700 new infections occurring each day [58]. Most of these occur in youngwomen resulting in the concomitant HIV epidemic in newborn childrencaused by the 18% mother-to-child transmission rate in South Africa [23].It is estimated that there are about 1.2 million AIDS orphans (970,000–1.4 million) in the country [21]. The HIV epidemic shows no signs of abatingin South Africa.

HIV-AIDS related mortality

Globally, AIDS has joined the leading causes of premature death amongboth women and men age 15 to 59 years of age [59,60]. Antiretroviral ther-apy has helped slow the rising mortality caused by AIDS: by the end of2005, it was estimated that 18 countries had met the ‘‘3 by 5’’ target of pro-viding treatment to at least half of those in need, and provision of antiretro-viral therapy in low- and middle-income countries has increased from400,000 at the end of 2003 to about 1.3 million at the end of 2005 [59].Less than 20%, however, of the estimated 4.7 million people in sub-SaharanAfrica in need of treatment at the end of 2005 were receiving such treatment[59]. Additional resources have been mobilized by the Global Fund to fightAIDS, tuberculosis, and malaria and the President’s Emergency Programfor AIDS Relief is helping to facilitate rapid scale up of treatment and pre-vention efforts.

In developed countries with well-established vital registration based ongood quality medical certification of underlying causes, the rise in AIDSdeaths before the introduction of highly active antiretroviral therapy was ev-ident. Since the introduction of highly active antiretroviral therapy in indus-trialized countries, these trends have changed and the AIDS mortality rateshave declined (Fig. 3) [48].

Unfortunately, this trend has not yet become evident in many developingcountries and mortality rates caused by AIDS continue to climb. As antire-troviral therapy becomes more widely available in these countries, however,it is hoped that trends seen in the United States (see Fig. 3) will be observed.In the meantime, AIDS currently remains among the leading causes of deathin many countries throughout the world.

Improving the understanding of the global epidemiology of HIV-AIDS:

future challenges

Despite major advances in the understanding of the epidemiology of HIVinfection in the past two decades, and increasing access to antiretroviraltreatment, HIV continues to spread unrelentingly and morbidity continuesto increase in many countries and regions across the globe. Much moreneeds to be done to understand the underlying contributing factors, thesocial and economic conditions that facilitate transmission of HIV.


Of particular concern are the evolving epidemics in Eastern Europe andparts of Asia through injecting drug use. Although HIV prevalence is stilllow in India and China, the absolute numbers of people infected area huge cause for concern, because the epidemic hitherto largely restrictedto sex workers and their clients could extend through bridging populationsto the general heterosexual population. In these settings, a deeper under-standing of what interventions are most appropriate to target bridgingpopulations is urgently needed.

As access to antiretroviral therapy expands across the globe, the impactof increased survival on HIV prevalence becomes evident. Vigilance isneeded to monitor the potential for behavioral disinhibition through in-creases in unsafe sexual practices among those on AIDS treatment, espe-cially because this may impact on stabilized epidemics in some populations.

Globally, women and young people are bearing an increasing and dispro-portionate burden of HIV infection. The unique risk factors responsible forthis disproportionate burden are not yet fully understood, and more data inthis regard are needed to improve prevention strategies aimed at thesegroups. More research is needed to understand the dynamics which may ex-plain the much higher prevalence and incidence in Southern Africa.

As the HIV epidemic continues to spread, much can be gleaned fromthose countries and populations where HIV has been successfully con-trolled. Given the scale of the disaster, detailed epidemiologic data are prov-ing critical to public health efforts to control the transmission of this virus.

Deaths

Persons living with AIDS

AIDS Cases

0

10

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1985 1987 1989 1991 1993 1995 1997 1999 2001 2003Years

(AID

S ca

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deat

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0

50

100

150

200

250

300

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(Per

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ith A

IDS

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Fig. 3. AIDS cases, deaths, and persons living with AIDS in the United States, 1985–2003.

(From US Centers for Disease Control and Prevention. AIDS surveillance: trends 1985–2004.

Available at: http://www.cdc.gov/hiv/topics/surveillance/resources/slides/trends/index.htm. Ac-

cessed November 2006.)

http://www.cdc.gov/hiv/topics/surveillance/resources/slides/trends/index.htm


Much more, however, still remains to be done as the virus itself, the riskgroups, and the epidemiology of HIV infection evolve in response to the im-plementation of prevention and treatment strategies.

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Documents

Global Epidemiology of HIV-AIDS