Page 33 - AIDSBK23C

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PATTERNS FOR HUMAN IMMUNODEFICIENCY VIRUS INFECTION

Worldwide, three patterns of HIV infection have been identified. In pattern 1, affecting
primarily urban areas of the Americas and western Europe, the majority of HIV infections occur
in males having sexual intercourse with other males (homosexual and bisexual males), followed
by infections in injection drug users. Fewer cases are observed among heterosexuals. Pattern 2
occurs in those areas in which HIV has been present longer and the number of HIV-infected
persons in the population is greater. Men and women are affected equally, and heterosexual
intercourse is the major means of transmission for HIV. These areas include sub-Saharan Africa
and parts of the Caribbean where HIV infection occurs throughout the heterosexual population,
and congenital AIDS is a significant problem. Pattern 3 occurs in areas of the world in which
HIV has been introduced only recently, defined risk groups have not emerged, and only sporadic
cases are reported.[188]

RISK GROUPS FOR HUMAN IMMUNODEFICIENCY VIRUS INFECTION

Risk groups for HIV infection based upon behavior patterns that put persons at risk are
detailed in Table 2. In countries such as the United States, through the first decade of the AIDS
pandemic, about half of AIDS cases were reported in men having sex with men (homosexual or
bisexual). The second largest risk group is comprised of injection drug users, accounting for
20% to 25% of reported AIDS cases in the United States. The percentage of HIV infections seen
in heterosexual adults (marital sex, casual sex, commercial sex workers) has increased over time
in developed nations. Pediatric AIDS in the United States and elsewhere is largely a function of
maternal risk factors, particularly from injection drug use. In countries of sub-Saharan Africa
and Asia, HIV infection is spread more widely in the population through heterosexually active
urban adults [3,115,189]
The demography of the spread of HIV depends upon the population subgroups into which
HIV has been introduced and the contact that other segments of the population have with them.
Thus, commercial sex workers and injection drug use may both be important means for spread of
HIV through the heterosexual population. AIDS among heterosexual adults in the United States
is increasing more than any other risk group, and over half of all heterosexually acquired HIV
infections occur in women. This represents a significant risk to the promiscuous or injection
drug using heterosexual person. Screening of blood products for HIV has virtually eliminated
the risk from transfusion or blood product therapy in locations where such screening is routinely
performed.[190]
On average, about 5 to 10% of persons who develop AIDS will report no identifiable risk
factor for HIV infection. Over time, many of them will be found to have a defined risk factor
when historical data becomes available. The number of cases of HIV infection with no
identifiable risk factor has not increased significantly over time, confirming the observation that
HIV infection is not acquired through casual contact.[115,171]