Development of the epidemic
BMJ 2001; 322 doi: https://doi.org/10.1136/bmj.322.7296.1226 (Published 19 May 2001) Cite this as: BMJ 2001;322:1226
This article has a correction. Please see:
- Michael W Adler
The first recognised cases of the acquired immune deficiency syndrome (AIDS) occurred in the summer of 1981 in America. Reports began to appear of Pneumocystis carinii pneumonia and Kaposi's sarcoma in young men, who it was subsequently realised were both homosexual and immunocompromised. Even though the condition became known early on as AIDS, its cause and modes of transmission were not immediately obvious. The virus now known to cause AIDS in a proportion of those infected was discovered in 1983 and given various names. The internationally accepted term is now the human immunodeficiency virus (HIV). subsequently a new variant has been isolated in patients with West African connections—HIV-2.
This article has been adapted from the forthcoming 5th edition of ABC of AIDS. The book will be available from the BMJ bookshop and at www.bmjbooks.com
AIDS defining conditions without laboratory evidence of HIV
Diseases diagnosed definitely
Candidiasis: oesophagus, trachea, bronchi, or lungs
Cryptococcosis: extrapulmonary
Cryptosporidiosis with diarrhoea persisting >1 month
Cytomegalovirus disease other than in liver, spleen, nodes
Herpes simplex virus (HSV) infection Mucocutaneous ulceration lasting >1 month Pulmonary, oesophageal involvement
Kaposi's sarcoma in patient <60 years of age
Primary cerebral lymphoma in patient <60 years of age
Lymphoid interstitial pneumonia in child <13 years of age
Mycobacterium avium: disseminated
Mycobacterium kansasii: disseminated
Pneumocystis carinii pneumonia
Progressive multifocal leucoencephalopathy
Cerebral toxoplasmosis
The definition of AIDS has changed over the years as a result of an increasing appreciation of the wide spectrum of clinical manifestations of infection with HIV. Currently, AIDS is defined as an illness characterised by one or more indicator diseases. In the absence of another cause of immune deficiency and without laboratory evidence of HIV infection (if the patient has not been tested or the results are inconclusive), certain diseases when definitively diagnosed are indicative of AIDS. Also, regardless of the presence of other causes of immune deficiency, if there is laboratory evidence of HIV infection, other indicator diseases that require a definitive, or in some cases only a presumptive, diagnosis also constitute a diagnosis of AIDS.
In 1993 the Centers for Disease Control (CDC) in the USA extended the definition of AIDS to include all persons who are severely immunosuppressed (a CD4 count <200×106 cells/l) irrespective of the presence or absence of an indicator disease. For surveillance purposes this definition has not been accepted within the UK and Europe. In these countries AIDS continues to be a clinical diagnosis defined by one or more of the indicator diseases mentioned. The World Health Organization (WHO) also uses this clinically based definition for surveillance within developed countries. WHO, however, has developed an alternative case definition for use in sub-Saharan Africa. This is based on clinical signs and does not require laboratory confirmation of infection. subsequently this definition has been modified to include a positive test for HIV antibody.
AIDS defining conditions with laboratory evidence of HIV
Diseases diagnosed definitely
Recurrent/multiple bacterial infections in child <13 years of age
Coccidiomycosis—disseminated
HIV encephalopathy
Histoplasmosis—disseminated
Isosporiasis with diarrhoea persisting >1 month
Kaposi's sarcoma at any age
Primary cerebral lymphoma: at any age
Non-Hodgkin's lymphoma: diffuse, undifferentiated B cell type, or unknown phenotype
Any disseminated myobacterial disease other than M tuberculosis
Mycobacterial tuberculosis
Salmonella septicaemia: recurrent
HIV wasting syndrome
Recurrent pneumonia within 1 year
Invasive cervical cancer
Diseases diagnosed presumptively
Candidiasis: oesophagus
Cytomegalovirus retinitis with visual loss
Kaposi's sarcoma
Mycobacterial disease (acid-fast bacilli; species not identified by culture): disseminated
Pneumocystis carinii pneumonia
Cerebral toxoplasmosi
These case definitions are complex and any clinician who is unfamiliar with diagnosing AIDS should study the documents describing them in detail.
HIV Transmission: global summary
Transmission of the virus
HIV has been isolated from semen, cervical secretions, lymphocytes, cell-free plasma, cerebrospinal fluid, tears, saliva, urine, and breast milk. This does not mean, however, that these fluids all transmit infection since the concentration of virus in them varies considerably. Particularly infectious are semen, blood, and possibly cervical secretions. The commonest mode of transmission of the virus throughout the world is by sexual intercourse. Whether this is anal or vaginal is unimportant. Other methods of transmission are through the receipt of infected blood or blood products, donated organs, and semen. Transmission also occurs through the sharing or reuse of contaminated needles by injecting drug users or for therapeutic procedures, and from mother to child. Transmission from mother to child occurs in utero and also possibly at birth. Finally, the virus is transmitted through breast milk.
Transmission of the virus
Sexual intercourse
Anal and vaginal
Contaminated needles
Injecting drug users
Needlestick injuries
Injections
Mother → child
In utero
At birth
Breast milk
Organ/tissue donation
Semen
Kidneys
Skin, bone marrow, corneas, heart valves, tendons, etc
The virus is not spread by casual or social contact. Health care workers can, however, be infected through needlestick injuries, and skin and mucosal exposure to infected blood or body fluids. Prospective studies in health care workers suffering percutaneous exposure to a known HIV seropositive patient indicate a transmission rate of 0.32%. As of December 1999 there have been 96 reported cases of documented seroconversion after occupational exposure in such workers.
The precautions and risks for such groups are covered in detail in chapter 15. Finally, there is no evidence that the virus is spread by mosquitoes, lice, bed bugs, in swimming pools, or by sharing cups, eating and cooking utensils, toilets, and air space with an infected individual. Hence, HIV infection and AIDS are not contagious.
Growth and size of the epidemic
Even though North America and Europe experienced the first impact of the epidemic, infections with HIV are now seen throughout the world, and the major focus of the epidemic is in developing/resource-poor countries.
Worldwide
The joint United Nations programme on AIDS (UNAIDS) has estimated that by the end of 1999 there were 34.3 million people living with HIV/AIDS (33.0 million adults and 1.3 million children <15 years). The new infections during that year were 5.4 million, approximately 15 000 new infections per day.
Regional HIV/AIDS statistics and features, end of 2000
Currently, 95% of all infections occur in developing countries and continents, the major brunt of the epidemic being seen in sub-Saharan Africa and South East Asia. It is now recognised that cases of AIDS were first seen in Central Africa in the 1970s even though at that time it was not recognised as such. Current surveys from some African countries show that the prevalence of infection is high amongst certain groups— 50-90% of prostitutes, up to 60-70% of those attending departments for sexually transmitted diseases and antenatal clinics. In the developing world, HIV is spread mainly by heterosexual intercourse.
At a family level, UNAIDS estimates that by the end of 1999 the epidemic has left behind a cumulative total of 13.2 million AIDS orphans (defined as those having lost their mother or both parents to AIDS before reaching the age of 15 years). Many of these maternal orphans have also lost their father. Orphans in Zimbabwe are expected to total 1 million by 2005 and 2 million in South Africa by 2010. Traditional family structures and extended families are breaking down under the strain of HIV. Population growth and death rates are increasingly affected. Life expectancy in countries with adult prevalences of over 10% (for example, Botswana, Kenya, Zimbabwe, South Africa, Zambia, Rwanda) are expected to see an average reduction in life expectancy of 17 years by 2010-2015. Young, highly productive adults die at the peak of their output, which has a considerable impact on a country's economy.
USA, UK and Europe
By June 1999, 702 748 adult cases of AIDS had been reported in the USA. In addition there were 8596 paediatric cases (<13 years old). Most of the cases in children (91%) occur because a patient suffered from HIV or belonged to a group at increased risk of HIV; 4% occurred through blood transfusion; 3% in children with haemophilia. Information on risk factors for the remaining 2% of the parents of these children is not complete.
Adult cases in Europe totalled 224 359 by June 1999, and those in the UK 12 780. There are five times more people infected with HIV at any one time than have AIDS. The rate for AIDS cases varies throughout Europe, with particularly high rates in Italy, Portugal, Spain, France and Switzerland, where the commonest mode of infection is through injecting drug use and the sharing of needles and equipment.
In North America and the UK the first wave of the epidemic occurred in homosexual men. In the UK, proportionally more homosexual men have been notified than in America: 66% of cases compared with 48% respectively. Even though infections amongst men who have sex with men still arise, an increasing proportion of new infections in the USA is occurring amongst injecting drug users sharing needles and equipment. There is also an increase amongst heterosexuals in both the USA and the UK. Currently in the USA, 16% of cases of AIDS have occurred amongst women, and although the commonest risk factor amongst such women is injecting drug use (42%), the next most common mode of transmission is heterosexual contact (40%).
The nature of the epidemic within the UK is changing with more heterosexual transmission. In the UK 12% of adult cases of AIDS have occurred in women, 70% of which have resulted from heterosexual intercourse. In 1999 there were more new annual infections of HIV than ever before and for the first time more occurring as a result of heterosexual sex than men having sex with men. Most heterosexually acquired infections are seen in men and women who have come from or have spent time in sub-Saharan Africa.
The advent of an antibody test in 1984 has allowed for a clearer understanding of the changing prevalence and natural history of HIV infection. Surveys show that the proportion of individuals infected needs to be high before cases of AIDS start to become apparent. It also underlines the importance of health education campaigns early in the epidemic, when the seroprevalence of HIV is low. Once cases of AIDS start to appear the epidemic drives itself and a much greater effort is required in terms of control and medical care.
Within countries one finds considerable variation in seroprevalence levels for HIV. Over 70% of cases of AIDS and HIV infection within the UK occur and are seen in the Thames regions (London and the surrounding area). Among different groups one also finds geographic differences. For example, the rates among drug users is higher in Edinburgh than London, and for gay men higher in London than anywhere else in the UK. This is also found in the developing world—for example, in Tanzania and Uganda, the urban level of HIV infection in men and women can be five times higher than rural rates.
HIV infected individuals diagnosed in the UK by exposure category: to end of 1999
The use of highly active antiretroviral therapy in resource-rich countries has resulted in an increase in life expectancy. This, in combination with the increase in new HIV infections, means that the prevalent pool of those infected, and potentially infectious, is increasing. This presents a continuing challenge for health promotion and a re-statement of the importance of safe sex techniques, particularly condom use.
AIDS: adult patient groups in the USA and UK
AIDS results in a considerable cost not only in human suffering, but also to health services. Other costs include time off work and the effect of the deaths of young people on national productivity. AIDS represents a major public health problem in the world. A clear understanding of the epidemiology forms the basis of developing a strategy or control ranging from health education to research.
The data on AIDS/HIV in the UK is reproduced with permission from the Communicable Disease Surveillance Centre (CDSC) and the United Nations AIDS Programme.