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1. Identification—Acquired Immunodeficiency syndrome (AIDS) is a term first used by epidemiologists concerned about the emergence in 1981 of a cluster of diseases associated with loss of cellular immunity in adults who had no obvious reason for presenting such immune deficien- cies. AIDS was subsequently shown to be the late clinical stage of infection with the human immunodeficiency virus (HIV). Within several weeks to several months after infection with HIV, many persons develop an acute self-limited mononucleosis-like illness lasting for a week or two. They may then be free of clinical signs or symptoms for months or years before other clinical manifestations develop. The severity of subsequent HIV-related opportunistic infections or cancers is, in general, directly correlated with the degree of immune system dysfunction.
   More than a dozen opportunistic infections and several cancers were considered to be sufficiently specific indicators of the underlying immu- nodeficiency for inclusion in the initial (1982) case definition of AIDS. If diagnosed by standard histological and/or culture techniques, these dis- eases were accepted as meeting the surveillance definition of AIDS cases, provided other known causes of immunodeficiency were ruled out.
   This definition was broadened in 1987 to include additional indicator diseases and to accept some of the indicator diseases as a presumptive diagnosis if laboratory tests showed evidence of HIV infection. In 1993, a revised surveillance definition of AIDS included additional indicator dis- eases. In addition, all HIV-infected persons with a CD4 cell count of under 200/mm3 or a CD4 T-lymphocyte percentage of total lymphocytes under 14%, regardless of clinical status, are regarded as AIDS cases. The 1993 definition continues to be generally accepted for clinical use in most industrialized countries; but it is often not used by developing countries, which lack adequate laboratory facilities for CD4 cell counts or for the histological or culture diagnosis of the surrogate indicator diseases.
   The history of WHO AIDS surveillance started with a provisional clinical case definition without serological confirmation and progressed to a revised definition formulated in Bangui, Central African Republic in 1994. Many countries now report new HIV infections rather than new AIDS cases. The revised African AIDS case definition incorporates HIV serolog- ical testing, if available, and includes a few indicator diseases (tuberculosis, pneumococcal disease and non-typhoid salmonellosis, which are not diseases of high virulence) as diagnostic in seropositive individuals.
   Bacterial pneumonia is one of the commonest presentations. The clinical manifestations of HIV infection in infants and young children overlap with failure to thrive, inherited immunodeficiencies and other
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childhood health problems. WHO and CDC have published paediatric AIDS case definitions.
The proportion of HIV-infected persons who, in the absence of anti-HIV treatment, will ultimately develop AIDS has been estimated at over 90%. In the absence of effective anti-HIV treatment, the AIDS case-fatality rate is high: survival time in many developing country studies is often under 1 year; in industrialized countries 80%–90% of untreated patients used to die within 3–5 years after diagnosis. Routine use of prophylactic drugs to prevent Pneumocystis carinii pneumonia and other opportunistic infec- tions in most industrialized countries significantly postponed the develop- ment of AIDS and death seen before effective anti-HIV treatment had become routinely available.
Serological tests for antibodies to HIV have been available commercially since 1985. The most commonly used screening test (EIA or ELISA) is highly sensitive and specific. The testing strategy depends on the purpose of testing. For surveillance purposes different strategies are recommended according to the expected level of HIV prevalence in the population tested. A single test is recommended in populations with a prevalence rate above 10%; lower prevalence levels require a minimum of 2 different tests for reliability. For diagnostic purposes a 3-test strategy for asymptomatic persons is recommended in populations with an HIV prevalence rate under 10% and a 2-test strategy in populations with higher rates. Selection of tests depends on factors such as accuracy and local operational characteristics. Different combinations of testing formats, EIA and rapid tests can be used. Confirmatory testing may include the Western blot or indirect fluorescent antibody (IFA) test. A nonreactive supplemental test negates an initial reactive EIA test; a positive reaction supports it; an indeterminate result in the Western blot test calls for further evaluation. Rapid testing techniques on blood or oral mucosal transudate facilitate delivery of testing and counselling services.
Most persons infected with HIV develop detectable antibodies within 1–3 months after infection. Other tests to detect HIV infection during the period after infection but prior to seroconversion are available; they include tests for circulating HIV antigen (p24) and PCR tests to detect viral nucleic acid sequences. The window period between the earliest possible detection of virus and seroconversion is short (less than 2 weeks). Antibody tests are thus rarely useful in diagnosing early HIV infection. Even for infants born of HIV-infected women these tests are of limited diagnostic value—passively transferred maternal anti-HIV antibodies often cause falsely positive anti-HIV EIA tests in these children even up to the age of 15 months.
The absolute T-helper cell (CD4 ) count or percentage is used most often to evaluate the severity of HIV infection and to help clinicians make decisions about treatment. Viral load tests are now available and serve as an additional marker of disease progression and response to treatment. The differential sensitivity of EIA and tests such as p24 antigenaemia has served to identify recent infections. A person reacting positively on the

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sensitive test and negatively on the less sensitive is likely to have been infected recently.
2. Infectious agent—Human immunodeficiency virus (HIV), a retro- virus. Two serologically and geographically distinct types with similar epidemiological characteristics, HIV-1 and HIV-2, have been identified. The pathogenicity of HIV-2 may be lower than that of HIV-1: they also have genotypic and phenotypic differences, with slower disease progression and lower rates of mother-to-child transmission for HIV-2.
3. Occurrence—AIDS was first recognized as a distinct clinical entity in 1981; in retrospect, however, isolated cases appear to have occurred during the 1970s and even earlier in several areas (Africa, Europe, Haiti, USA). Of the estimated 40 million persons (34 – 46 million) living with HIV infection or AIDS (HIV/AIDS) worldwide in 2003, the largest elements were estimated at 25–28.2 million in sub-Saharan Africa, 4.6 – 8.2 million in south and southeastern Asia, 13–1.9 million in Latin America and 800 000–1 million in North America. Globally, AIDS caused an estimated 3.1 million deaths in 2003 (2.5–3.5 million); the epidemic has continued growing, with estimates of 5 million new infections (4.2–5.8 million) and 2.5 million children (2.1–2.9 million) living with HIV/AIDS. HIV-1 is the most prevalent HIV type throughout the world; HIV-2 has been found primarily in western Africa, with cases also in countries linked epidemio- logically to western Africa.
In many developing countries numbers of AIDS cases are much higher, but reporting is poor and monitoring efforts have focused on HIV infections rather than AIDS cases. In several industrialized countries, the distribution of AIDS cases by risk behaviours or factors has shifted over the past decade. For example, although the AIDS epidemic in the USA continues to affect primarily men who have sex with men, intravenous drug use (IDU) is the main source of infection in other countries such as the former Soviet Union.
In the USA and other industrialized countries, annual HIV incidence decreased shortly before the mid-1980s and has remained relatively low since then in most groups. However, in the most severely affected countries in sub-Saharan Africa, annual HIV incidence has continued almost unabated at high levels. Outside sub-Saharan Africa, high HIV prevalence rates (more than 1%) in the 15–49 year old population have been noted in the Caribbean and in south and southeastern Asia. China and India, more recently infected, remain of major concern epidemiologically.
4. Reservoir—Humans. HIV is thought to have recently evolved from chimpanzee viruses.
5. Mode of transmission—Person to person transmission through unprotected (heterosexual or homosexual) intercourse; contact of abraded skin or mucosa with body secretions such as blood, CSF or semen; the use of HIV-contaminated needles and syringes, including sharing by intravenous drug users; transfusion of infected blood or its components;

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and the transplantation of HIV-infected tissues or organs. The risk of HIV transmission through sexual intercourse is lower than for most other sexually transmitted agents. However, the presence of a concurrent sexually transmitted disease, especially an ulcerative one, can facilitate HIV transmission. The primary determinants of sexual transmission of HIV are patterns and prevalence of sexual risk behaviours such as unprotected intercourse (no condom—a.k.a. unprotected sex) with many concurrent or overlapping sexual partners.
HIV can also be transmitted from mother to child (MTCT or vertical transmission). From 15% to 35% of infants born to HIV-positive mothers are infected through placental processes at birth. HIV-infected women can transmit infection to their infants through breastfeeding and this can account for up to half of mother-to-child HIV transmission. Giving pregnant women antiretrovirals such as zidovudine results in a marked reduction of MTCT.
Up to mid-1999, the only drug shown to reduce the risk of perinatal HIV transmission was azidothymidine (AZT) when administered orally after the 14th week of pregnancy and continued up to delivery; administered intravenously during the intrapartum period; and administered orally to the newborn for the first 6 weeks of life. This chemoprophylactic regimen was shown to reduce the risk of perinatal transmission by 66%. A shorter course of AZT treatment has been shown to reduce the risk of perinatal transmission by about 40%.
After direct exposure of health care workers to HIV-infected blood through injury with needles and other sharp objects, the rate of serocon- version is less than 0.5%, much lower than the risk of hepatitis B virus infection after similar exposures (about 25%). Unsafe injections may account for up to 5% of transmission.
It cannot be sufficiently stressed that carriers are usually asymptomatic; they—and their potential partners—are therefore unaware of their poten- tial infection status.
While the virus has occasionally been found in saliva, tears, urine and bronchial secretions, transmission after contact with these secretions has not been reported. The risk of transmission from oral sex is not easily quantifiable, but is presumed to be low. No laboratory or epidemiological evidence suggests that biting insects have transmitted HIV infection.
6. Incubation period—Variable. Although the time from infection to the development of detectable antibodies is generally 1–3 months, the time from HIV infection to diagnosis of AIDS has an observed range of less than 1 year to 15 years or longer. The median incubation period in infected infants is shorter than in adults. The increasing availability of effective anti-HIV treatment since the mid-1990s has reduced the development of clinical AIDS in most industrialized countries.
There is some evidence that disease progression from HIV infection to AIDS is more rapid in developing countries than in other populations. The only factor that has been consistently shown to affect progression from

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HIV infection to the development of AIDS is age at initial infection: adolescent and adults (males and females) who acquire HIV infection at an early age progress to AIDS more slowly than those infected at an older age. Disease progression may also vary somewhat by viral subtype.
7. Period of communicability—Not known precisely; begins early after onset of HIV infection and presumably extends throughout life. Infectivity during the first months is considered to be high; it increases with viral load, with worsening clinical status and with the presence of other STIs. Free or cell-associated virus occurs in secretions and hence ulcerative or inflammatory STIs are a risk factor.
8. Susceptibility—Unknown, but presumed to be general: race, gen- der and pregnancy status do not appear to affect susceptibility to HIV infection or AIDS. There is increasing evidence of host factors such as chemokine-receptor polymorphisms that may reduce susceptibility. The presence of other STIs, especially if ulcerative, increases susceptibility, as may the fact of not being circumcised for males, a factor possibly related to the general level of penile hygiene. Interactions between HIV and other infectious disease agents have caused great medical and public health concern. The major interaction identified so far is with Mycobacterium tuberculosis infection. Persons with latent tuberculous infection who are also infected with HIV develop clinical tuberculosis at an increased rate, with a lifetime risk of developing tuberculosis that is multiplied by a factor of 6 – 8. This interaction has resulted in a parallel pandemic of tuberculosis: in some urban sub-Saharan African populations where 10%–15% of the adult population have dual infections (Mycobacterium tuberculosis and HIV), annual incidence rates for tuberculosis increased 5- to 10-fold during the latter half of the 1990s. No conclusive data indicate that any infection, including M. tuberculosis infection, accelerates progression to AIDS in HIV-infected persons. Other adverse interactions with HIV infection include pneumococcal infection, non-Typhi salmonellosis, falciparum malaria and visceral leishmaniasis.
9. Methods of control—
A. Preventive measures: HIV/AIDS prevention programs can be effective only with full community and political commitment to change and/or reduce high HIV-risk behaviours.

1. Public and school health education must stress that having multiple and especially concurrent and/or overlapping sex- ual partners or sharing drug paraphernalia both increase the risk of HIV infection. The specific needs of minorities, persons with different primary languages and those with visual, hearing or other impairments must also be ad- dressed. Students must be taught the skills needed to avoid or reduce risky behaviours. Programs for school-age youth

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should address the needs and developmental levels of both
students and those who do not attend school.
2) Theonlyabsolutelysurewaytoavoidinfectionthroughsex is to abstain from sexual intercourse or to engage in mutually monogamous sexual intercourse only with some- one known (preferably through serology) to be uninfected. In other situations, latex condoms must be used correctly every time a person has vaginal, anal or oral sex. Both male and female latex condoms with water-based lubricants have
been shown to reduce the risk of sexual transmission.
3) Expansion of facilities for treating drug users reduces HIV transmission. Programs that instruct needle users in decon- tamination methods and needle exchange have been shown
to be effective.
4) HIVtestingandcounsellingisanimportantinterventionfor
raising awareness of HIV status, promoting behavioural change and diagnosing HIV infection. HIV testing and counselling can be undertaken for:
a) persons who are ill or involved in high-risk behaviours, who may have a test for diagnostic purposes;
b) attenders at antenatal clinics, to diagnose maternal in- fection and prevent vertical transmission;
c) couple counselling (marital or premarital);
d) anonymous and/or confidential HIV counselling and
testing for the “worried well”.
5) AllpregnantwomenmustbecounselledaboutHIVearlyin pregnancy and, where culturally and socially appropriate, encouraged to undertake an HIV test as a routine part of standard antenatal care. Those found to be HIV-positive may wish to take a course of ARV treatment, where this is on offer, to reduce the risk of their infant being infected. There is some evidence that exclusive breastfeeding is associated with lower transmission rates than partial breastfeeding.
6) AlldonatedunitsofbloodmustbetestedforHIVantibody; only donations testing negative can be used. People who have engaged in behaviours that place them at increased risk of HIV infection should not donate plasma, blood, organs for transplantation, tissue or cells (including semen for artificial insemination). Organizations that collect plasma, blood or other body fluids or organs should inform potential donors of this recommendation and test all do- nors. When possible, donations of sperm, milk or bone should be frozen and stored for 3–6 months before use. Donors who test negative after that interval can be consid- ered not to have been infected at the time of donation.

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7) Physicians should adhere strictly to medical indications for transfusions. The use of autologous transfusions should be encouraged.
8) Only clotting factor products that have been screened and treated to inactivate HIV must be used.
9) Care must be taken in handling, using and disposing of needles or other sharp instruments. Health care workers should wear latex gloves, eye protection and other personal protective equipment in order to avoid contact with blood or with fluids. Blood should be washed off with soap and water without delay. These precautions must be taken in the care of all patients and in all laboratory procedures
10) WHO recommends immunization of asymptomatic HIV- infected children with the EPI vaccines; those who are symptomatic should not receive BCG vaccine. Live Measles- Mumps-Rubella and polio vaccines are recommended for all HIV-infected children.
B. Controlofpatient,contactsandtheimmediateenvironment:

1. Report to local health authority: Official reporting of AIDS cases is obligatory in most countries. Official reporting of HIV infections is required in some areas, Class 2 (see Reporting). Where nominal reporting is not the rule, care must be taken to protect patient confidentiality.


2. Isolation: Isolation of the HIV-positive person is unnecessary, ineffective and unjustified. Universal precautions apply to all hospitalized patients. Observe additional precautions appro- priate for specific infections that occur in AIDS patients.


3. Concurrent disinfection: Of equipment contaminated with blood or body fluids and with excretions and secretions visibly contaminated with blood and body fluids by using bleach solution or germicides effective against M. tuberculo- sis.


4. Quarantine:Notapplicable.Patientsandtheirsexualpartners should not donate blood, plasma, organs for transplantation, tissues, cells, semen for artificial insemination or breastmilk for human milk banks.


5. Immunization of contacts: Not applicable.


6. Notificationofcontactsandsourceofinfection:Theinfected
   patient should ensure notification of sexual and needle- sharing partners whenever possible. Notification by the health care provider is justified only when the patient, after due counselling, still refuses to notify his/her partner(s), and when health care providers are sure that notification will not entail harm to the index case. Care must be taken to protect patient confidentiality.

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7) Specifictreatment:Earlydiagnosisofinfectionandreferralfor medical evaluation are indicated. Consult current sources of information for appropriate drugs, schedules and doses, including the WHO and UNAIDS websites.
a) Prior to the development of relatively effective antiretro- viral treatment, which, in the industrialized countries, has become routinely available since the mid-1990s, treatment was available only for the opportunistic diseases that complicated HIV infection. Prophylactic use of oral tri- methoprim-sufamethoxazole, with aerosolized pentami- dine as a less effective backup, is recommended to prevent P. carinii pneumonia. All HIV infected persons should receive tuberculin skin tests and be evaluated for active TB. If this is found, patients should be placed on antituberculosis treatment. If no active TB is found, pa- tients who are tuberculin-positive or are anergic but were recently exposed should be offered preventive treatment with isoniazid for 12 months (recommended duration varies).
b) AIDSmustbemanagedasachronicdisease;antiretroviral treatment is complex, involving a combination of drugs: resistance will rapidly appear if a single drug is used. The drugs are toxic and treatment must be lifelong. Adherence is critical for the success of the treatment. A successful treatment is not a cure, although it results in suppression of viral replication. Decisions to initiate or change antiret- roviral treatment must be guided by the laboratory param- eters of both plasma HIV RNA (viral load) and CD4 T cell count, and by assessing the clinical condition of the patient. Laboratory results provide important information about the virological and immunological status of the patient and the risk of progression to AIDS. Once the decision to initiate antiretroviral treatment has been made, treatment should be aggressive with the goal of maximal viral suppression. In general, a protease inhibitor and two non-nucleoside reverse transcriptase inhibitors should be used initially. Other regimens may be used but are con- sidered less than optimal. Special considerations apply to adolescents and pregnant women, with specific treatment regimens for these patients.
c) Precautions to minimize the risk of HIV transmission in health care settings must be implemented worldwide. Management of persons, especially health care workers, exposed to blood and other body fluids suspected of containing HIV is complex. The factors to consider before recommending postexposure prophylaxis (PEP) includes

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the nature of the exposure, whether the exposed worker might be pregnant, and the local occurrence of drug- resistant HIV strains. As of late 1999, recommendations for PEP include a basic 4-week regimen of two drugs (zidovu- dine and lamivudine) for most HIV exposures, as well as an expanded regimen that includes the addition of a protease inhibitor (indinavir or nelfinavir) for HIV expo- sures that pose an increased risk of transmission or where resistance to one or more of the antiretroviral agents recommended for PEP is known or suspected. Health care organizations should have protocols that promote and facilitate prompt access to postexposure care and report- ing of exposures.
C. Epidemic measures: HIV is currently pandemic, with large numbers of infections reported in the Africa, the Americas, southeastern Asia, and Europe. See 9A (Preventive measures) for recommendations.
D. Disasterimplications:Emergencypersonnelshouldfollowthe same universal precautions as health workers. If latex gloves are not available and skin surfaces comes into contact with blood, this should be washed off as soon as possible. Masks, visors and protective clothing are indicated when performing procedures that may involve spurting or splashing of blood or bloody fluids. Emergency transfusion services should use blood donations screened for HIV antibody; when it is not possible to test donated blood, donations should be accepted only from donors who have engaged in no HIV-risk behaviours and preferably from donors who have previously tested negative for HIV.
E. International measures: The United Nations Joint Programme on HIV/AIDS (UNAIDS), which coordinates UN activities, and WHO do not endorse measures such as requirements for AIDS or HIV examinations for foreign travellers prior to entry.