Sande's HIV/AIDS Medicine

562 Pages·2012·9.496 MB·English

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1
Chapter
The global epidemiology of HIV/AIDS
IrumZaidi,KevinM.DeCock
globalepidemicandshowsgreatgeneticdiversitywithnine
OVERVIEW OF THE GLOBAL EPIDEMIC subtypes(A–D,F–H,J,andK)andatleast48circulating
recombinant forms. HIV-1 groups N, O, and P are rare
and essentially restricted to persons from Central Africa.
There have been tremendous changes in the global HIV
ThesinglemostcommonsubtypeofHIV-1issubtypeC,
epidemicsincethe1990swithdeclinesinincidentinfec-
whichaffectsnearly17millionpeopleinsouthernAfrica,
tions,increasedcoverageofantiretroviraltherapy,stabili-
partsofEastAfrica,andAsia[2].ThenumberofHIV-2in-
zationordeclinesinHIVprevalence,reductionofmother-
fectionsgloballyissmallandseemstobedecreasing;most
to-child transmission, and reduction in AIDS-related
areassociatedwithWestAfrica.
deaths.Manyoftheseadvancesresultedfromthedramatic
increaseinHIVprograminvestmentsinlow-andmiddle-
income countries, which grew from US$1.4 billion in
2001 to US$15.9 billion in 2009. These resources
MEASUREMENT OF DISEASE
havesupportedHIVtreatmentforover6millionpeople
worldwide[1].
Nonetheless, even with the recent stabilization of the Methods for measuring HIV incidence and prevalence
global epidemic, HIV/AIDS has had devastating impact continuetoevolvetomoreaccuratelymeasurediseasebur-
on lives worldwide and especially in sub-Saharan Africa. den[3].Theprogressionofthedisease,latemanifestation
Therewereanestimated33.3million(31.4–35.3million) of symptoms, HIV testing behaviors, and antiretroviral
peoplegloballylivingwithHIVattheendof2009,anum- therapy all challenge our ability to use epidemiologic
berthatmaycontinuetoincreaseasincidentcasescontinue and laboratory methods to measure HIV incidence and
toaccrueanddeathstofallsecondarytoantiretroviralther- prevalence[4,5].
apy.AdecreaseinnewHIVinfectionshasoccurred,from Surveillancemethodshavedrasticallyimprovedwithin
an estimated 3.1 million (2.9–3.4 million) in 2001 to the past decade. In low- and middle-income countries,
2.6million(2.3–2.8million)in2009[1]. sentinel surveillance among pregnant women attending
Thereisgenetic,epidemiologic,andbehavioralheteroge- antenatalclinicshasbeenthecornerstoneofeffortstoesti-
neityintheglobalHIVepidemic,withdifferentregionsdis- mateHIVprevalenceinthegeneralpopulation.Pregnant
proportionatelyimpactedbythevirus.Generalizedspread womenarebydefinitionsexuallyactive,giveinsightinto
has occurred in sub-Saharan Africa while HIV/AIDS else- prevalencetrendsinthegeneralpopulation,andareeasy
wherehaslargelybeenrestrictedtokeyvulnerablepopula- tosurveysincetheyaccesshealthservices[6].Thecoverage
tions(menwhohavesexwithmen,injectingdrugusers, andqualityofthissurveillanceapproachhasimprovedto
andsexworkersandtheirclients)[1]. providemorerepresentativedata[7].
Phylogenetically,twotypesofHIVarerecognized,HIV-1 CountrieswithgeneralizedHIVepidemics,meaningthat
andHIV-2;withinHIV-1therearefourgroups,groupM, HIV transmission is sustained in the general population
group N, group O, and group P and within HIV-2, eight outsideofcoregroups,haveinadditionbeenconducting
groups. HIV-1 group M is the predominant cause of the periodic national household surveys toestimate national
3
Section |1| EpidemiologyandbiologyofHIVinfection
HIVprevalenceandcollectbehavioralinformationrelated with men, and special studies can address diverse issues
to HIV acquisition and transmission. Arbitrarily, an HIV suchasaccesstoandadherencetotherapyorthespectrum
prevalencegreaterthan1%hassometimesbeenassumed ofdiseaseinpeoplelivingwithHIV.
to indicate generalized spread, although this assumption Casereportingrequiresuseofastandardcasedefinition
isunreliable.Severalhigh-burdencountrieshavenowcon- whichisasurveillancetool,andnotintendedforclinical
ductedmorethanonehouseholdsurvey,usuallyatapprox- managementofpatients.Forclinicalpurposes,stagingsys-
imately 5-year intervals, to monitor trends and measure tems can help assist clinicians define where individual
impactofHIVprograms.Thesenationalsurveysareused patientslieonthespectrumofHIV-associatedimmunode-
to adjust prevalence levels from sentinel site surveillance ficiency and disease. Different casedefinitions have been
in pregnant women to more accurately reflect those of usedovertimeasunderstandingofHIV/AIDSandsurveil-
thegeneralpopulation.Commonexperiencehasbeenthat lance practices evolved, and taking account of local re-
inrelationtonationallyrepresentativehouseholdsurveys, sourcesforinvestigationandreportingofcases.
sentinel site surveillance based on pregnant women att- Therevised2006casedefinitionsandstagingsystempro-
ending antenatal clinics has tended to overestimate HIV posedbyWHOprovidestandardizeddefinitionsforglobal
prevalence. This realization was key to UNAIDS and the usetoimprovepatientmanagement,patientmonitoring,
World Health Organization (WHO) lowering global HIV and surveillance [9, 10]. Four clinical stages and four
estimatesconsiderablyinlate2007[3]. immunological stages were established (Table 1.1a and
Countrieswithlow-levelorconcentratedepidemicscon- 1.1b), reflecting the known decline in clinical status and
duct biological and behavioral surveys among high-risk CD4cellswiththeprogressionofHIVdisease.Thesurveil-
populations, which include injection drug users, men lancedefinitionsforHIV/AIDSwerealsorevisedtoinclude
whohavesexwithmen,andmaleandfemalesexworkers. three categories: HIV infection, advanced HIV disease,
Newmethodsforaccessinghigher-riskpopulationsthatare and AIDS (Box 1.1). Although a standard case definition
oftenhardtoreachcontinuetobevalidated[8].Recently, forprimary(acute)HIVinfectionisnotestablished,iden-
countrieswithgeneralizedepidemicshavealsobeencon- tifyingandreportingcasesofprimaryinfectionmaybeim-
ducting biological and behavioral surveys among higher- portant because these represent very recent infections.
riskpopulationsthataredisproportionatelyaffectedeven Symptomatic primary HIV infection presents one to four
in generalized epidemics. An important epidemiologic weeks after HIV acquisition and may include any of the
exercise has been estimating the respective population followingsymptoms:
sizesofthesehigh-riskgroups,allowingestimatesoftheir (cid:129) Lymphadenopathy;
total numbers of HIV infections and contributions to (cid:129) Pharyngitis;
overallHIVinfectionincidence,whichisusefulforalloca- (cid:129) Maculopapularrash;
tion of resources for prevention of different modes of (cid:129) Orogenitaloroesophagealulcers;
transmission. (cid:129) Menigoencephalitis;
In high-income, industrialized countries such as the (cid:129) Lymphopenia(includinglowCD4);and
UnitedStatesandcountriesinEurope,whichhaveconcen- (cid:129) Opportunisticinfections.
trated epidemics, individual AIDS case reporting was for
These clinical conditions should not be confused with
a long time the basis for monitoring epidemiologic
clinical staging criteria. Primary HIV infection can be
trends. Because of the long incubation period between
diagnosed by recent HIV antibody development or by
HIV infection and disease, AIDS case surveillance reflects
identifying HIV products (HIV-RNA or HIV-DNA and/or
patterns of HIV transmission that were prevalent several
ultrasensitive HIV p24 antigen with a negative HIV
yearsearlier.Withtheadventofantiretroviraltherapythe
antibodytest).
predictable progressiontoAIDSwasinterrupted, thusse-
verelylimitingtheabilityofAIDSdatatogiveinsightinto
HIVtransmissionpatterns.Asaresult,theimportanceof
HIV infection case reporting was considerably enhanced.
Today,high-incomecountrieswithrobustsurveillancesys- Table1.1a WHOclinicalstagingofestablished
temstrackbothHIVandAIDScasereports,butbothgive HIVinfection
incompleteinformation.
HIV case reports reflect HIV incidence imperfectly be- HIV-ASSOCIATED WHOCLINICAL
cause they require HIV-infected persons to be tested and SYMPTOMS STAGE
reported.AIDScaseratesareaffectedbypreviousHIVinci-
Asymptomatic 1
dencebutalsobytheeffectivenessofHIVdiagnosis,access
toantiretroviraltherapy,andresponsetotreatment.Foras Mildsymptoms 2
completeaspossibleanunderstandingoftheHIV/AIDSep-
idemic,inadditiontocasereportingthereisalsoaneedfor Advancedsymptoms 3
surveysandspecialstudies.Surveysincludebehavioraland
Severesymptoms 4
biologicstudiesinspecialgroupssuchasmenwhohavesex
4
Chapter |1| TheglobalepidemiologyofHIV/AIDS
Table1.1b WHOimmunologicalclassificationforestablishedHIVinfection
HIV-ASSOCIATED AGE-RELATEDCD4VALUES
IMMUNODEFICIENCY
<11mo 12–35mo 36–59mo (cid:1)5yrs
(%) (%) (%) (permm3)
None/notsignificant >35 >30 >25 >500
Mild 30–35 25–30 20–25 350–499
Advanced 25–30 20–25 15–20 200–349
Severe <25 <20 <15 <200or<15%
Box1.1 WHOcasedefinitionforHIVinfectionforreportingforadultsandchildren
1. Adults,andchildren18monthsandolder: 2. ImmunologiccriteriafordiagnosisofadvancedHIVin
DiagnosisofHIVinfectionismadewith: adultsandchildren(cid:1)5years,withdocumentedHIV
PositiveHIVantibodytesting(rapidorlaboratory- infection:
basedEIA).ThisisusuallyconfirmedbyasecondHIV CD4countlessthan350/mm3inanHIV-infectedadultor
antibodytest(rapidorlaboratory-basedEIA)relyingon child.
differentantigensorondifferentoperating 3. ImmunologiccriteriafordiagnosisofadvancedHIVin
characteristics. achild<5yearsofagewithdocumentedHIV
And/or infection:
PositivevirologicaltestforHIVoritscomponents %CD4<30inthose(cid:3)11monthsofage;
(HIV-RNAorHIV-DNAorultrasensitiveHIVp24antigen) %CD4<25inthoseaged12–35months;and
confirmedbyasecondvirologicaltestobtainedfroma %CD4<20inthoseaged36–59months.
separatedetermination.
2. Childrenyoungerthan18months: 1Whereaccesstovirologicaltestinginchildrenlessthan
DiagnosisofHIVinfectionismadewith: 18monthsislimited,confirmationofHIVinfectioncanbe
PositivevirologicaltestforHIVoritscomponents obtainedfromrepeattestingonthesamespecimenwhere
(HIV-RNAorHIV-DNAorultrasensitiveHIVp24antigen) laboratoryqualityassurance,includingspecimenhandlingis
confirmedbyasecondvirologicaltestobtainedfroma guaranteed.
separatedeterminationtakenmorethan4weeksafter 2AIDSinadultsandchildrenisdefinedasclinicaldiagnosis
birth[1]. (presumptiveordefinitive)ofanyonestage4condition(as
Positiveantibodytestingisnotrecommendedfor definedinannex1);ORimmunologicalcriteriainadultsand
definitiveorconfirmatorydiagnosisofHIVinfectionin children>5yearswithdocumentedHIVinfectionfirst-ever
childrenuntil18monthsofage. documentedCD4countlessthan200/mm3or%CD4<15;or
WHOcriteriafordiagnosisofadvancedHIV inachild<5yearswithdocumentedHIVinfectionfirst-ever
(includingAIDS[2])forreportingforadultsand documentedCD4of%CD4<25inthoseinfants(cid:3)11
children monthsofage;%CD4<20inthoseaged12–35months,or
1. ClinicalcriteriafordiagnosisofadvancedHIVin %CD4<15inthoseaged35–59months.
adultsandchildrenwithdocumentedHIV Note:AIDScasereportingisnolongerrequiredifHIV
infection: infectionoradvancedHIVinfectionisreported.
Presumptiveordefinitivediagnosisofanyonestage3or
stage4condition.
Countries with established national HIV case surveil-
HIV TRANSMISSION
lance systems (mostly Western countries) use back-
calculation methods or direct calculation to determine
HIVprevalenceandincidence[4,11].Othercountriesrely HIVistransmittedfrompersontopersonthroughhetero-
onepidemicmodelsbasedondatafromsurveillanceofkey sexualandmale-to-malesexualintercourse;throughexpo-
populationstoestimateHIVprevalenceandincidenceand suretoinfectedbloodorbloodproducts;andfrommother
monitortrends[12]. to child, including through breastfeeding. Surveillance
5
Section |1| EpidemiologyandbiologyofHIVinfection
plays an important role in quantifying the proportional Injection drug use and exposure to
contribution of different modes of transmission to the contaminated blood
overallepidemicinanycountry,allowingrationalresource
allocationforprevention,treatment,andcaretodifferent Thereareanestimated15.9million(11–21million)injec-
groups. torsworldwide,andinjectiondruguseisanincreasingphe-
nomenongloballythatisextendingintoregionswhereit
was previously not seen. Eastern Europe has the highest
Sexual transmission
ratesofinjectiondruguse(Fig.1.1),whichiscoupledwith
Most HIV infections are transmitted sexually, with hete- highratesofHIVamongthispopulation.Overall,thereare
rosexualtransmissionbeingthedominantmodeoftrans- anestimated3millionHIV-positivedruginjectorsworld-
mission globally. As with all modes of transmission, widewiththemajorityresidinginChina,Russia,andthe
infectiousness isdetermined by viralload: thehigherthe UnitedStates[18].
viral load, the more likely that transmission will occur. AlthoughHIVinfectionfromexposuretocontaminated
Othersexuallytransmittedinfections,especiallyulcerative bloodandbloodproductswasrecognizedearlyonasan
conditionsincludingHSV-2infection,increaseviralshed- importantmodeoftransmission,transfusionsafetyinitia-
ding in genital fluids and transmissibility [13]. Male cir- tiveshaveessentiallyeliminatedorverygreatlyreducedthe
cumcision is partially protective (approximately 50–60% riskofacquiringHIVinfectionfromcontaminatedblood.
efficacy) against heterosexual acquisition of HIV [14]. AlthoughtheriskofHIVtransmissionthroughneedlestick
Althoughthereisnodefinitiveevidencethatmalecircum- injury is well understood (0.003 risk of transmission
cisionprotects against male-to-female transmission, indi- for uncomplicated needlesticks from an infected source),
rectbenefittowomenwillultimatelyresultfromreduced therelativecontributionofsuchnosocomialeventstoover-
HIVprevalenceinmen.TheriskofHIVinfectionincreases allnumbersofHIVinfectionsinhigh-burdensettingshas
withthenumberofsexpartners,andbecauseoftheirhigh beendifficulttoquantify[19].
viralload,personsrecentlyinfectedmaycontributedispro-
portionatelytospread[15].ThehighestratesofHIVinfec-
tionarefoundinpersonswiththegreatestrateofpartner
REGIONAL REVIEW
changesuchassexworkers.Thereisdebateabouttheepi-
demiologicimpactofconcurrentversussequentialpartner-
ships, theformer suggested asestablishing more efficient Sub-Saharan Africa
transmission networks. In the generalized epidemics of
southern and eastern Africa, a substantial proportion of Although two-thirds ofallHIV-infected persons residein
heterosexually transmitted infections occur in stable or sub-Saharan Africa, this most heavily affected part of the
long-termsero-discordantcouples. world has seen substantial epidemiologic changes over
HighratesofHIVinfectionarefoundamongmenwho the past 10 years, with a decrease in new HIV infections
havesexwithmenalmosteverywheretheyhavebeenstud- and deaths and stabilizing or declining HIV prevalence.
ied.Recognitionthatmale-to-malesexoccursinvirtually Sub-SaharanAfricaillustratesbetterthananyotherregion
allcountries,includinginsub-SaharanAfrica,isrelatively thesocial,economic,demographic,andmedicalimpactof
recent,asisthedocumentationofhighratesofHIVinfec- HIV/AIDSwhichaccountedfortheunprecedentedglobal
tioninmenwhohavesexwithmeninsocietiessuffering healthresponse.
generalizedHIVepidemics[16]. Striking heterogeneity characterizes the sub-Saharan
African epidemic, with the highest rates of infection in
Mother-to-child transmission southernAfricancountries,followedbycountriesinEast,
West,andCentralAfrica(Fig.1.2).Twenty-fivepercentof
HIV can be transmitted from mother to child in utero, allpersonslivingwithHIVinsub-SaharanAfricaresidein
around delivery, or after birth during breastfeeding. SouthAfrica.Althoughratesofinfectionareextremelyhigh
Prophylaxis or treatment with antiretroviral drugs has inneighboringcountries,theirsmallpopulationsmeanthat
drastically reduced the vertical transmission rate, which absolutenumbersofinfectedpersonsarelimited.Nigeria,
without intervention ranges from about 15% in non- whichhasamuchlowerHIVprevalencethancountriesin
breastfeeding women to 45% for those breastfeeding up southernAfrica,accounts for15%ofAfricanslivingwith
to24months[17]. HIV,andcountriesofEastAfricaforonequarter[1].
ThegreatmajorityofHIV-infectedwomenresideinsub- HeterosexualtransmissionaccountsformostoftheHIV
SaharanAfricawheretheoverallHIVprevalenceinwomen transmissioninsub-SaharanAfricaandwomencontribute
aged15–24wasestimatedat3.4%;in2009therewerean approximately60%ofallHIVinfections.Serialageandsex-
estimated370,000childrennewlyinfectedwithHIV,with specificprevalenceshowswomenareinfectedatyounger
themajority ofthese infections occurring insub-Saharan agesthanmen,presumablyareflectionofoldermenwith
Africa. HIV having sex with younger women. A relatively recent
6
Chapter |1| TheglobalepidemiologyofHIV/AIDS
No reports of injecting drug use identified
Injecting drug use reported but no estimate of prevalence
1%
0.5% – < 1%
0.25% – < 0.5%
> 0% – < 0.25%
Figure1.1 Globalprevalenceofinjectiondruguse.
ReprintedfromtheLancet.MathersBM,DegenhardtL,PhillipsB,etal.GlobalepidemiologyofinjectingdruguseandHIVamongpeoplewhoinject
drugs:asystematicreview.Lancet2010;375:1014–1028.CopyrightElsevier2010.
No data
< 0.1%
0.1% – < 0.5%
0.5% – < 1%
1% – < 5%
5% – < 15%
> 15% – < 20%
Figure1.2 GlobalprevalenceofHIV,2009.
FromUNAIDS.Globalreport:UNAIDSreportontheglobalAIDSepidemic2010.WithpermissionofUNAIDS=ONUSIDA2010.
7
Section |1| EpidemiologyandbiologyofHIVinfection
recognitionisthatsub-SaharanAfricaalsohasanepidemic West
ofHIVamongmenwhohavesexwithmenandthatmany
West Africa has considerable virologic diversity, with all
ofsuchmenalsohavesexualrelationswithwomen.Most
subtypesandcirculatingrecombinantformsfoundinthis
studies have shown higher HIV prevalence among men
sub-region[2].NigeriahasthelargestHIVepidemicinthe
whohavesexwithmenthanamongexclusivelyheterosex-
sub-region,withanestimatedadultprevalenceof3.6%and
ualmales,intherangeofapproximately12–30%[16].
3.3millionpersonslivingwithHIV.Otherscountrieswith
Although approximately 70% of AIDS-related deaths
higher prevalence are Coˆte d’Ivoire, Ghana, and Togo,
worldwide occur in sub-Saharan Africa, AIDS-related
countriesthathavebeencloselylinkedbytradeandmove-
mortality on the continent has declined with scale-up of
mentofpeople.Most countrieshaveeitherstabilizingor
antitretroviraltherapy[1].
decreasing HIV epidemics, although Sierra Leone (1.1%
in2001to1.6%in2009)andGambiahaveshownincreas-
South ingadultHIVprevalence(0.6to2.0%inGambia).
HIV incidence estimates indicate slowing epidemics in
CountriesinsouthernAfricahavethehighestratesofHIV
many countries in the sub-region, with Coˆte d’Ivoire,
intheworldwiththelargestnumberofpeoplelivingwith
Guinea-Bissau,andGhanashowingthegreatestreduction
HIVinSouthAfrica,anestimated5.6million.Lackofmale
inincidentinfections.Withthereductionofincidence(and
circumcision, high rates of HSV-2, intergenerational sex,
prevalence) in Guinea-Bissau and other countries with
and highrates ofpartner change consequent upon large-
HIV-2, the overall prevalence of HIV-2 is also decreasing
scalemigrationforworkalllikelycontributedtogenerating
to less than one million infections worldwide [2]. Data
and sustaining these severe epidemics. Swaziland has
fromCoˆted’Ivoirealsoillustrateareductioninbehaviors
the highest adult HIV prevalence (25.9%) in the world.
relatedtoHIVtransmissionamongmenandwomenwith
BotswanaandLesothoalsohaveextremelyhighprevalence
decreasing HIV prevalence, including among young
(24.8%, 23.6%), while HIV prevalence in Angola (2%)
women 15–24 years attending antenatal clinics [21].
is very low compared to other countries within the sub-
ThelowerprevalenceofHIVinfectioninWestAfricathan
region[1].TheprolongedcivilwarinAngolaseemstohave
inothersub-regionsislikelytobedueinparttohighrates
hadaprotectiveeffectagainstHIVbylimitingtravelandin-
ofmalecircumcision[23].
teractions with other countries in the region with higher
HIVprevalence[20].
Incidenceestimatessuggestdecreasingnumbersofnew Central
infections since 2001 in almost all countries in southern
CameroonandtheDemocraticRepublicofCongo(DRC)
Africa,withBotswana,Namibia,Swaziland,andZimbabwe
have the greatest HIV-1 genetic diversity in the world,
experiencingthegreatestrelativedeclines.Additionally,in
withnearlyallsubtypesandCRFinthesecountries.HIV
Malawi,Namibia,Zambia,andZimbabwe,measurement
prevalence in this sub-region is stabilizing, with some
ofsexualbehaviorsshowsdeclinesinthepercentofpeople
countries experiencing a decrease in incident infections.
whohadhadsexbytheageof15–19years,whohadmore
Cameroon has the greatest number of persons infected
thanonepartnerinthepastyear,andwhohadmorethan
(610,000), with an overall adult HIV prevalence of
onepartnerinthepastanddidnotusecondoms[21].HIV
5.3%. The Republic of Congo shows the lowest adult
prevalenceishigheramongyoungwomenthanyoungmen
HIV prevalence, 3.4%. Incidence estimates in the region
inmostofthecountriesinthesub-region.
showdecreasingnewinfectionsintheCentralAfricanRe-
public,Congo,andGabon[1].Datafromsurveillancein
East antenatalclinicsintheDRCalsoillustratedecliningprev-
alence among antenatal clinic attendees from 2004 to
TheHIVepidemicinEastAfricashowssignofslowingand
2009[24].
stabilization. Although adult HIV prevalence rates are
lower in the sub-region than in southern Africa, ranging
from2.9%inRwandato6.3%inKenya,theactualnumber Europe
ofpeoplelivingwithHIVishighgiventhelargepopula-
tionsinEastAfricancountries[1].Overalltheremayhave Therewereanestimated2.2millionpeoplelivingwithHIV
beenchangesinHIVriskbehaviorsandlikelyreducedHIV inWHO’sEuropeanRegionwhosecountrieshaveHIVand
incidenceincountriessuchasEthiopia,Kenya,andTanza- AIDScasereportingsystemsofvaryingcompleteness.Ato-
nia,butpatternsofchangearediverse[21].InUganda,for tal of 53,427 cases of HIV were diagnosed and reported
example, there is concern that gains in HIV prevention from49ofthe53countriesintheWHOEuropeanRegion
achievedearlyonintheepidemicarebeingreversed[22]. in 2009 (case surveillance data were not available from
While antenatal HIV prevalence has declined in Kenya in Austria, Monaco, Russia, and Turkey). There were a total
the early part of this century, the trend in antenatal HIV of 6,568 AIDS cases reported in 2009 (Austria, Sweden,
prevalenceinUgandahasbeenupwards[22]. Monaco, Russia, and Turkey did not report) and 1,776
8
Chapter |1| TheglobalepidemiologyofHIV/AIDS
casesdiagnosedwithAIDSwerereportedtohavedied,al- hasdoubledsince2001,withmostinfectionsamongdrug
mosthalftheAIDS-relateddeathsreportedin2008[25]. injectors.HIVprevalenceamonghigh-riskpopulationsin
The three sub-regions within Europe have differing epi- Moscow show elevated prevalence among injection drug
demics,withEasternEuropeexperiencingincreasingHIV users (15.6%), men who have sex with men (8.3%),
incidencerelatedtoinjectiondruguse;HIVepidemicsin and female sex workers (4.5%) [1]. With an estimated
thecentralandwesternsub-regionsseemtobestablewith 1.8millioninjectiondrugusersinRussia,theHIVepidemic
HIV infection rates remaining similar over the past five amongthispopulationisincreasingandanimportantpub-
years. lic health challenge since HIV-infected drug injectors can
drivesecondarytransmissiontosexpartnersandchildren
asaresultofmother-to-childtransmission[18].
West
In 2009, 24,703 cases of HIV infection were newly diag-
Central
nosed from 21 of 23 countries in the sub-region, a rate
of6.7per100,000.Seventy-twopercentofcasesdiagnosed Atotalof1,612casesofHIVwerediagnosedin2009(all14
wereamongmalesand10%ofcaseswereinpersons15–24 countriesreporting);arateof1.4per100,000.Themajority
years old. Nearly half(40%) ofthe cases diagnosed with ofcasesdiagnosedwereamongmales(80%)and19%of
HIV in 2009 resulted from heterosexual transmission, the cases were in persons between 15 and 24 years of
many of which were in persons originating from sub- age. Of the cases reported with risk factor information
SaharanAfrica.Theremainingcasesdiagnosedwereamong (63%),one-thirdidentifiedmale-to-malesexasthemode
men who have sex withmen (37%), among whom rates oftransmission,whichrepresentsadoublingsince2004.
have consistently increased since 2004, and 4% were Heterosexualtransmissionremainedrelativelystablesince
among injecting drug users in whom rates have been 2004 (24% of cases) while injection drug use increased
steadily declining. Less than 1% of cases were the result 157%since2004(8%ofcases),thoughtheabsolutenum-
ofperinataltransmission,transfusions,ornosocomialin- berofinjectiondrugusecasesremainsmall.Atotalof404
fections. A total of 4,361 AIDS cases were diagnosed in AIDScaseswerediagnosedin2009from14ofthe15coun-
2009 from 20 of 23 countries in the western sub-region, triesinthecentralsub-region,withanoverallAIDSrateof
withanoverallAIDSrateof1.1per100,000[25]. 0.3per100,000.
East North America
In 2009, 27,112 HIV cases were diagnosed and reported
United States
from 14 of the 15 countries in the eastern sub-region
(Russiadidnotreport,andthereporteddatathereforerep- Withanestimated1.1millionpeoplelivingwithHIV,the
resent a serious underestimate of the sub-region’s epi- United Statesisthemostheavilyaffectedcountryinthe
demic). Fewer than half the cases (41%) were among industrialized world [26, 27]. In the 40 states that have
femalesand14%among15–24yearolds.Although46% stable HIV reporting systems, the rate of HIV diagnoses
of cases diagnosed in 2009 identified heterosexual trans- was17.4per100,000in2009[27].AIDSreportingfrom
missionasthemodeoftransmission,thismaybeanunder- all 50 states shows an AIDS diagnosis rate of 11.2 per
estimate because of unrecognized or unreported sexual 100,000 in 2009. In 2008, the death rate of persons
transmission from partners who inject drugs, such as in withHIV(thecauseofdeathmayormaynothavebeen
GeorgiaandAzerbaijan[25]. HIV-related)was7.0per100,000population,aratethat
Overall, heterosexual transmission has increased since has been stable since 2006. Deaths in persons reported
2004alongwiththeoverallrateofnewHIVreportsinthe with AIDS were 5.3 per 100,000, a 7% annual decrease
sub-region(11.3per 100,000in2004and18.9in2009). from2006.
Injectiondruguseaccountedfor39%ofreportedcaseswhile TheoverallrateofHIVdiagnosesseemstohavestabi-
perinataltransmissionandtransmissionamongmenwho lizedsince2006withanestimated42,000diagnosesper
havesexwithmenaccountedforlessthan3%ofthecases; year.Malesaccountfor76%ofHIVdiagnoses,witharate
perinatal transmission has doubled in the past two years, of32.7per100,000,constantsince2006,whiletherateof
andmale-to-maletransmissionhasalsoincreasedalthough diagnosesamongwomenhasslightlydecreasedto9.8per
thereportednumbersremainrelativelysmall.In2009,atotal 100,000in2009.TherehasbeenanincreaseinHIVdiag-
of1803AIDScaseswerediagnosedfrom13ofthe14coun- noses among younger age groups (15–19 and 20–24
tries,withanoverallAIDSrateof1.3per100,000.Underre- years) as well as in the older age group of 55–59 years.
portingfromcountriesinthissub-regionissubstantialand HIVdiagnosesamongchildrenlessthan13yearsdueto
datapresentedareanunderestimate[25]. perinatal transmission continued to decrease, with an
Recentresultsfromepidemicmodelingsuggestthatthe estimated 131 children diagnosed in 2009, maintaining
HIV epidemic in Russia (1% HIV prevalence in 2009) theprecipitousdeclineinmother-to-child transmissionof
9
Section |1| EpidemiologyandbiologyofHIVinfection
HIVinfections,theirrate(7.2per100,000)wasaboutnine
Table1.2 DiagnosesofHIVInfectionamongadults
timeslowerthanthatinAfricanAmericans;thelowestover-
andadolescents,2009—40statesand5USdependent
allrateofreportedHIV infectionswas inAsians (6.4per
areas
100,000)(Table1.2).In2008,33%ofpeoplediagnosed
withHIValsoreceivedanAIDSdiagnosiswithinoneyear,
No. %
indicatingHIVisbeingdiagnosedrelativelylate.
Transmissioncategory
Male-to-malesexualcategory 24,312 56.4 Canada
Injectiondruguse 4,172 9.7 The HIV epidemic seems to be stable in Canada, with
approximately 65,000 people estimated to be living with
Male-to-malesexualcontact 1,157 2.7 HIV. The majority of new infections are among men
andIDU
who have sex with men and heterosexuals from HIV en-
Heterosexualcontacta 13,257 31.0 demic countries. The indigenous Aboriginal population
isdisproportionatelyaffected[28].
Otherb 75 0.2
Race/ethnicity
Latin America and the Caribbean
AmericanIndian/AlaskaNative 91 0.04
Caribbean
Asian 293 1.2
Thereareanestimated240,000peoplelivingwithHIVin
Black/AfricanAmerican 10,135 42.0 the Caribbean region. With an estimated prevalence of
HIVinfectionof1%,theCaribbeanisthesecondhighest
Hispanic/Latinoc 4,692 19.4 burdened region in the world. Overall, more women
(53%) are estimated to be living with HIV than men,
NativeHawaiian/OtherPacific 22 0.1
but this is greatly influenced by the epidemic in Haiti
Islander
where61%ofinfectionsareamongwomen.TheBahamas
White 8,613 35.7 hasthehighestestimatedadultHIVprevalenceinthere-
gion, 3.1%, although there has been a decrease in HIV
Multipleraces 287 1.2
prevalence among 15- to 24-year-old pregnant women
inthepast10years[1,21].Othercountriesintheregion
Source:CentersofDiseaseControlandPrevention.HIV
havelessthan2%prevalence.MostcountriesintheCarib-
SurveillanceReport,2009;vol21.http://www.cdc.gov/hiv/topics/
surveillance/resources/reports.PublishedFebruary2011.Accessed bean have concentrated epidemics with elevated HIV
April9,2011. prevalence in key populations including sex workers and
Note:DataincludepersonswithadiagnosisofHIVinfection men who have sex with men [29]. Haiti stands out as
regardlessofstageofdiseaseatdiagnosis.Alldisplayeddatahave an exception, having been affected earliest and demon-
beenstatisticallyadjustedtoaccountforreportingdelaysand
strating a predominantly heterosexual epidemic. AIDS-
missingrisk-factorInformation,butnotforincompletereporting.
aHeterosexualcontactwithapersonknowntohave,ortobeat related deaths have decreased in the sub-region since
highriskfor,HIVinfection. 2001 by 37%, with an estimated 12,000 AIDS-related
bIncludeshemophilia,bloodtransfusion,perinatalexposure,and deathsin2009 [1].
riskfactornotreportedornotidentified.
cHispanics/Latinoscanbeofanyrace.
Centraland South America
Thereareanestimated1.4millionpeoplelivingwithHIV
HIV since the 1990s. Male-to-male sex accounted for inLatinAmerica,slightlyhigherthanin2001,withanes-
over half of the new cases diagnosed in 2009 followed timatedadultHIVprevalenceof0.5%.However,therehas
by heterosexual contact (31%) and injection drug use been a reduction in new infections since 2001, down to
(Table1.2). 92,000newinfectionsin2009.Belizehasthehighestadult
OverhalfofHIVdiagnosesin2009wereamongAfrican HIV prevalence (2.3%), with most countries having a
Americans,witharateof66.6per100,000,thehighestrate prevalencebelow1%.OverhalfofHIV-infectedpersonsre-
acrossallracialandethnicgroups.Thesecondmosthighly side in three countries: Brazil, Argentina, and Columbia.
affectedgroupbyraceorethnicitywereHispanicsandLa- Inmostofthecountriesinthesub-regionHIVprevalence
tinoswhoaccountedfor17%ofinfectionswitharateof isslightlyhigheramongyoungmalesthanyoungfemales,
22.8per100,000.Althoughwhitesaccountedfor28%of with the exception of Belize and Guyana. Similar to the
10
Chapter |1| TheglobalepidemiologyofHIV/AIDS
Caribbean and North America, the epidemic is concen- adults living with HIV), which was lower than the 1.2%
tratedamonghigh-riskpopulations. adult prevalence in 2001. AIDS-related deaths decreased
HIV seroprevalence surveys in capital cities show ele- byalmosthalfin2009to3100deathsamongadultsand
vated prevalence specifically among men who have sex children.IncontrastHIVprevalencehasincreasedinIndo-
withmenandfemalesexworkers.Georgetown,Guyana, nesiawheretherearenow300,000adultslivingwithHIV
hasthehighestHIVprevalenceamongfemalesexworkers foraprevalenceof0.2%.Althoughthemajorityofinfec-
(16.6%), followed by San Salvador (4.1%). Prevalence tionsareamonghigh-riskgroups,therearegeographicdif-
among men who have sex with men is also higher than ferencesandinthegeneralpopulationofTanahPapauthe
in the general population; in recent surveys their preva- prevalence was 2.4% [31]. Indonesia, like many other
lencerangedfrom 20.3%in Santiago, Chile, to4.2%in countries in the sub-region, has a high HIV prevalence
Nicaragua[1]. among injection drug users in the capital city (52.4% in
More data are also available on population size esti- 2007),asdoThailand(38.7%,2009),Myanmar(36.3%,
mates for high-risk groups. For example, in El Salvador 2008),Cambodia(24.4%,2007),andPakistanandNepal
there are an estimated 12,500 men who have sex with (21%)[1].
men(3.4%ofmen)and7000femalesexworkers(1.4%
of women)[30]. Triangulating the population size esti-
matesforhigh-riskgroupswiththeirHIVprevalenceesti- East Asia
mates provides valuable insights into the risks and
Thereareanestimated770,000personslivingwithHIVin
preventionneedsofmaleandfemalepartnersandclients
thefivecountriesofEastAsia,with96%oftheinfectionsin
ofsexworkers.
China,whichrepresentsanadultHIVprevalenceof0.1%,
the highest in the sub-region. Although females only ac-
count for 32% of infections the proportion has been in-
Asia
creasing since 2001, along with the overall increasing
Overallanestimated4.9millionpeoplearelivingwithHIV prevalence inChina. The rateofnewinfections seemsto
intheAsiaregion,foranestimatedstableHIVprevalencein be stabilizing, with an estimated 48,000 new infections
adultsof0.4%.HIVincidenceinAsiaappearstohavede- in2009.Modesoftransmissionhavebeenchangingover
creasedslightlyfrom2001to360,000newinfectionsannu- theyears,withmostrecentestimatesshowingasmallin-
ally,withanestimated300,000totalAIDS-relateddeaths crease in the proportion of men who have sex with men
in 2009. Overall more men are infected with HIV (66% infected.GiventhevastsizeofChina,thereareimportant
of all infections) in this region, although HIV infections geographicvariations,withsixprovincescarryingover70%
among women seem to be increasing. Thailand has the ofthediseaseburden(Yunnan,Guangxi,Henan,Sichuan,
highestadultprevalenceintheregion,estimatedat1.3%, Xinjiang, and Guangdong) [32]. Estimated AIDS-related
indicating about 520,000 persons living with HIV, lower deathswere26,000in2009,suggestingastabilizationof
than the 1.7% prevalence estimated for 2001. India ac- mortalityinrecentyears.
countsfor almosthalfofall HIV infectionsinthe region,
with2.4millionpersonslivingwithHIV,whichrepresents
anadultHIVprevalenceof0.3%.HIVinfectionintheregion CentralAsia and Middle East
isprimarilyconcentratedamonghigh-riskgroupsincluding
In2009therewereanestimated60,000peoplelivingwith
injectiondrugusers,sexworkersandtheirclients,andmen
HIVintheCentralAsiasub-region,withHIVprevalence
whohavesexwithmen,althoughthereisgreatvariationre-
apparently increasing among certain populations, espe-
gionallyinthecontributiontotheepidemicfromspecific
ciallyinjection drugusers[33]. Adult HIV prevalencein
riskgroups[1].
2009 was highest in Kyrgyzstan at 0.3% and lowest in
Uzbekistan and Kazakhstan at 0.1%. There are an esti-
mated247,500injectiondrugusersinCentralAsia,with
South and SoutheastAsia
HIVprevalencerangingfrom17.6%inDushanbeto2.9%
HIVepidemicsinthisregionofAsiaaremainlyamongin- inAstana[18].
jectiondrugusers,femalesexworkers,andtheirclients.Al- TheHIVepidemicintheMiddleEast(includingcoun-
thoughHIVprevalenceestimatesremainlow,theincrease triesinNorthAfrica)remainsthelowestburdenedinthe
intheestimatednumbersorpersonslivingwithHIVsug- world,concentratedamongcertainriskgroups,primarily
gests there may be emerging, concentrated epidemics in injection drug users and men who have sex with men
countrieslikeBangladesh,Nepal,Pakistan,andthePhilip- [34].Sudanhasthehighestprevalenceinthesub-region,
pines.Othercountries,suchasCambodia,Myanmar,and withanestimated260,000peoplelivingwithHIV,which
ThailandexhibitdecreasingHIVprevalence.In2009,Cam- accountsforoverhalfoftheestimated460,000intheentire
bodiahadanestimated0.5%adultHIVprevalence(56,000 sub-region[1].
11
Section |1| EpidemiologyandbiologyofHIVinfection
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