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The Acquired Immunodeficiency
Syndrome: Epidemiology and Risk
Factors for Transmission
Kenneth C. Castro, M.D.,* Ann M. Hardy, Dr.P.H.,* and
James W. Curran, M.D., M.P.H. t
EPIDEMIOLOGY OF AIDS
Acquired immunodeficiency syndrome (AIDS) was first recognized in
the spring of 1981, when the Centers for Disease Control (CDC) received
reports of multiple cases of two rare diseases, Pneumocystis carinii pneumonia and Kaposi's sarcoma, occurring in young, previously healthy homosexual men from New York City and California. 5, 6 All these patients had
similar patterns of underlying immunosuppression without any apparent
cause. Because of the unusual and severe nature of these diseases, the
CDC established a task force to study this apparently new syndrome.
An early observation was that patients with AIDS had a specific
impairment in the cell-mediated component of the immune system and
that they developed diseases predictive of this impairment. 31, 45, 57 This
observation was used to formulate the case definition that the CDC uses
for surveillance purposes. The CDC defines AIDS as a reliably diagnosed
disease at least moderately predictive of underlying cellular immune
deficiency occurring in a person with no known underlying cause of immune
deficiency or other cause of reduced resistance associated with that disease. 10, 56 Eleven opportunistic infections and diseases are considered specific enough to be indicative of AIDS (Table 1). Because the surveillance
case definition was designed with more emphasis on specificity than
sensitivity, the cases of AIDS represent only the "tip of the iceberg" of the
disease spectrum (Fig. 1). Other disease entities, such as non-Hodgkin's
*Medical Epidemiologist, AIDS Program, Center for Infectious Diseases, Centers for Disease
Control, Public Health Service, V. S. Department of Health and Human Services, Atlanta,
Georgia
tDirector, AIDS Program, Center for Infectious Diseases, Centers for Disease Control, Public
Health Service, V.S. Department of Health and Human Services, Atlanta, Georgia
Medical Clinics of North America-Vol. 70, No. 3, May 1986
635
636
KENNETH
G. CASTRO, ANN.\1. HARDY, AND JA:-'IES \V. CURRAN
Table 1. Opportunistic Diseases Considered to Be Indicative of AIDS
PROTOZOAL INFECTIONS
FUNGAL INFECTlOl'iS
Pneumocystis carinii pneumonia
Toxoplasma gondii encephalitis or disseminated
infection (excluding congenital infection)
Chronic (> 1 month) Cryptosporidium enteritis
Noncongenital Viral Infections
Chronic (> 1 month) mucocutaneous herpes
simplex
Histologically evident cytomegalovirus
infection of an organ other than liver or
lymph node
Progressive multifocal leukoencephalopathy
Candida esophagitis
Cryptococcal meningitis or disseminated
infection
Bacterial infection
Disseminated (not just pulmonary or
lymphatic)
Mycobacterium avium-intracellulare
Cancers
Kaposi's sarcoma (in a person under
age 60)
Primary brain lymphoma (limited to
the brain)
lymphoma, generalized unexplained lymphadenopathy, thrombocytopenia,
and oral candidiasis, are part of the AIDS disease spectrum, as well as
infection with the virus without signs or symptoms. 7, 40, 47
Recent laboratory and epidemiologic evidence indicates that a retrovirus is the cause of AIDS. 3, 17, 29, 41, 42, 61 Three morphologically similar
prototype isolates, termed lymphadenopathy-associated virus (LA V), human
T-celllymphotropic virus type III (HTLV-III), and AIDS-associated retrovirus (ARV), have been described,3, 29, 42 and represent independent isolates
of the same virus group. These retroviruses have been isolated from patients
with AIDS, AIDS-related conditions such as generalized lymphadenopathy,
and asymptomatic members of groups with an increased incidence of
AIDS. 3 , 28, 29. 32, 42, 62 Antibodies to HTLV-IIIILAV have been found in 68%
to 100% of AIDS patients and patients with AIDS-related conditions,41, 42.
54, 55 and in 22% to 87% of high-risk-group members.17, 30, 46, 53, 59, 61 In
contrast, antibodies have been detected in less than 1% of persons with no
known risk for AIDS.22a, 41, 42, 46, 54, 55, 61 In one longitudinal study, all the
patients who developed AIDS had anti-HTLV-I11/LAV detected before
there was clinical evidence of disease. 30
The surveillance case definition was recently revised to include other,
more severe clinical manifestations of HTLV-IIIILAV infection. 22 In the
"Iceberg"
Known
Possible
Figure 1. Clinical spectrum of
AIDS.
Other malignancies,
Unexplained lymphadenopathy.
Idiopathic thrombocytopenic
purpura,
Transient immunologic defects,
Asymptomatic carriers
AIDS:
637
EPIDE:'vIlOLOCY A;\ID RISK FACTORS FOR TRANS:'vIISSIOl\:
4500
Reported Cases of AIDS by Half Year of Report
United States, January 21, 1986
4000
3500
Figure 2. AIDS cases by
half-year of report in the United
States, 1981 through 1985. *Includes a backlog of cases identified at the beginning of the
CDC surveillance.
~ 3000-
~ 2500-
~
;
z
2000---'
1500--'
1000 -
o~'-~"
.....--___
19B1
1982
1983
1984
1985
absence of the opportunistic diseases required by the previous AIDS
surveillance case definition, any of the following diseases is considered
indicative of AIDS if the patient has a positive serologic or virologic test
for HTLV-III/LAV:
• Disseminated histoplasmosis, diagnosed by culture, histology, or
antigen detection.
• Isosporiasis, causing chronic diarrhea (> 1 month), diagnosed by
histology or stool microscopy.
• Bronchial or pulmonary candidiasis, diagnosed by microscopy or by
the presence of characteristic white plaques on the bronchial mucosa.
• Non-Hodgkin's lymphoma of high-grade pathologic type and of Bcell or unknown immunologic phenotype, diagnosed by biopsy,
• Histologically confirmed Kaposi's sarcoma in patients who are 60
years of age or older (when diagnosed).
• Histologically confirmed diagnosis of chronic interstitial pneumonitis
in a child under 13 years of age,
Revision of the AIDS case definition resulted in the reclassification of
less than 1% of cases previously reported to CDC, The number of AIDS
cases reported to the CDC is steadily increasing (Fig, 2), By January 21,
1986, 16,574 (16,343 adult, 231 pediatric) cases of AIDS had been reported
in the United States, The first cases of AIDS in the United States were
diagnosed in 1978, Statistical analysis of the trends indicates that cases will
continue to increase substantially through 1986. 25a Thirty-four per cent of
AIDS cases have been reported from New York (Fig. 3); most of these are
New York City residents, California (primarily San Francisco and Los
Angeles) reported 23% of the cases. Other states with more than 500 cases
include Florida (1102 cases), New Jersey (1005 cases), and Texas (884 cases),
Cases of AIDS in adults can be divided into six patient categories that
suggest a possible means of disease acquisition (Table 2), These categories
are arranged hierarchically, so that each patient falls into only the first
appropriate category, Seventy-three per cent of the cases are reported in
638
KE]';"ETH
G.
CASTRO,
AN" M.
HARDY, A~D JAMES
W.
CCRRAN
AIDS Cases in the United States
January 21, 1986
!y
~30e.AA
(N=16,574)
.~
!
1"5639
\
4
RI
77 eT
1005NJ
- 245MD
- 21
DE
Other U.S.
Territories
6
PR
.CJ
188
Figure 3. AIDS cases by state of residence at onset of illness.
homosexual or bisexual men. Past or present abusers of intravenous (IV)
drugs compose 17% of the total. More than half the women with AIDS are
IV drug abusers. One per cent of the patients are hemophiliacs, and another
1% were heterosexual partners of persons in one of the first three groups.
Approximately 2% were recipients of single-donor blood transfusions in the
7 years before diagnosis of AIDS. Finally, 6% of the cases cannot be
classified into any of these categories. This includes 399 persons born in
Haiti or central Africa, where most AIDS cases have not been associated
with known risk factors.
More than half the patients with AIDS were reported with P. carinii
pneumonia, 18% with Kaposi's sarcoma, 6% with both P. carinii pneumonia
Table 2. Reported Cases of AIDS in Adults, by Patient Characteristic and
Gender, United States, June 1981-January 21, 1986
WOME]I;
MEN
PATIENT GROUP
Homosexual or bisexual man
Intravenous drug user
Hemophiliac
Heterosexual con tact
Transfusions with blood/blood
products
Other
Total
No.
%
11,998
2206
128
27
162
79
14
1
<1
1
747
15,268
5
No.
TOTAL
%
572
4
158
101
53
<1
15
9
240
107.5
22
No.
%
11,998
2778
132
165
263
73
17
1
1
2
987
16,343
6
AIDS:
639
EPIDEYlIOLOGY AND RISK FACTORS FOR TRANSMISSION
Table 3. Reported Cases of AIDS, by Disease Category and
Case:Fatality Ratio, United States, June 1981-January 21, 1986
AIDS CASES
CASE,
r;O.OF
FATALITY
PRIMARY DISEASE
No.
%
DEATHS
RATIO (%)
KS without pep
Both KS and pep
pep without KS
or without KS or pep
Total
3056
920
9539
3059
16,574
18
6
58
18
1167
598
4986
1672
8423
38
65
52
55
51
KS = Kaposi's sarcoma. pep = Pneumocystis carinii pneumonia. or = other opportunistic infection.
and Kaposi's sarcoma, and 18% with another opportunistic disease only
(Table 3). The distribution of diseases varies by patient category. Homosexual or bisexual men are more likely to have Kaposi's sarcoma than the other
groups. P. carinii pneumonia is more common in IV drug users and
hemophiliacs.
Fifty-one per cent of patients are reported to have died. Mortality
varies both by disease group and by time from diagnosis of AIDS. Patients
with Kaposi's sarcoma alone appear to have a lower mortality than those in
other disease groups (Table 3). The reported mortality increases as time
from diagnosis of AIDS increases. For patients diagnosed prior to 1983, the
mortality is 77%. Patients diagnosed in 1983 have a 73% mortality, those
diagnosed in 1984 have a 61% mortality, and 31% of those diagnosed in
1985 have died. No patients with definite AIDS have been reported to
have recovery of immune function, although a very small percentage
survive.
The age distribution of AIDS patients has remained relatively constant:
about 90% are between the ages of 20 and 49. Forty-seven per cent are
between 30 and 39 years old. The racial/ethnic distribution of AIDS patients
is as follows: 60% are white, 25% are black, and 14% are Hispanic. Fewer
than 1% of patients are Asian, even though the United States, especially
New York City and San Francisco, has a large Asian population.
The CDC has received reports of 231 children (127 boys, 104 girls)
under the age of 13 who meet a provisional case definition for pediatric
AIDS.15 Six (3%) of these children were diagnosed with Kaposi's sarcoma,
133 (58%) had P. carinii pneumonia (4 also had Kaposi's sarcoma), and 92
(40%) had another opportunistic disease. One hundred thirty-seven (59%)
of these children are known to have died. The pediatric cases can also be
divided into four patient categories: 11 of the children have hemophilia, 33
received blood transfusions, and 175 have at least one parent who belongs
to a risk group for AIDS. The remaining 12 patients cannot be classified.
Cases of AIDS have also been reported from over 47 countries other
than the United States. Canada has reported 248 cases, and the 21 European
countries that make up the World Health Organization European Collaborating Centre on AIDS have reported 1573 cases. 22d. 49. Most cases in these
countries have been reported in homosexual or bisexual men. AIDS has
also been reported from Haiti50. 51 and several countries in Central M-
640
KENNETH
C. CASTRO, ANN M. HARDY, AND JAMES W. CURRAN
rica. 24 . .52. 60 Few of the cases in these countries have been in homosexual
men or IV drug users. Most of these patients were heterosexual, with a
male-to-female ratio of 1.1:1 reported in Zaire. 52 Risk factors for the
occurrence of AIDS in Haitians and Central Africans are currently being
investigated, with heterosexual transmission being the presumed mode of
AIDS transmission.
RISK FACTORS FOR HTLV-IIIILAV TRANSMISSION
Homosexuality
Because more than 70% of those with AIDS in the United States are
homosexual men, much attention has been focused on the transmission of
HTLV-III/LAV in this group. A national case-control study carried out by
the CDC compared 50 homosexual men with AIDS with 120 healthy
homosexual men selected from outpatient clinics and private physician
practices. 38 The most important variables in differentiating AIDS cases from
controls were measures of homosexual activity. AIDS cases had a larger
number of male sex partners per year, began having sex at an earlier age,
and were more likely to have had syphilis and non-B hepatitis than were
controls. Although AIDS cases used a greater variety of "street" drugs over
their lifetime than did controls, no one drug was associated with AIDS.
AIDS cases were also more likely than controls to have inserted their
tongue ("rimming") or hand (" fisting") into a partner's rectum within the
last year; however, a substantial proportion of cases never engaged in either
of these activities.
Another case-control study, carried out in New York City, compared
20 men with Kaposi's sarcoma with 40 homosexual controls from a private
physician's practice. 44 This study also found that the number of male sex
partners in the year prior to diagnosis was significantly higher in AIDS
cases. Other important variables identified included anal-receptive intercourse and "fisting."
The sexual transmission hypothesis generated by the two case-control
studies was further strengthened by the discovery of a cluster of AIDS
cases linked by sexual contact. 2 When 13 of the first 19 AIDS patients
reported from southern California were interviewed, nine were found to
have had sexual contact with one or more AIDS patients within the 5 years
of onset of symptoms. An AIDS patient who did not live in California was
found to have had sex with four of these nine California patients and also
with AIDS patients in New York City. Ultimately, the investigators were
able to link 40 AIDS patients in 10 different cities by sexual contact,
accounting for over 16% of the first 248 cases of AIDS reported in
homosexual men in the United States.
Serologic studies for antibodies to the implicated retrovirus in asymptomatic homosexual men have yielded seropositivity rates ranging from
22% to 65%.17.30,46,61 In a cohort of homosexual men attending a city clinic
in San Francisco, the seroprevalence of anti-HTLV-IIIILAV has increased
from 4.5% (13 of 290) in 1978 to 24,1% (7 of 29) in 1980 and 67.4% (293 of
AIDS:
641
EPIDEMIOLOGY Al'\D RISK FACTORS FOR TRA:-ISYIISSION
AIDS in Adults by Risk Group
United States, January 21, 1986
N=16343
Homosexual/Bisexual Men
11998
Hemophilia/Coagulation
132 Disorder
138
G
L
~
Ur-
None of the
Other Groups
Heterosexual
Contacts*
Ce3\
~ Transfusion
Recipients*
IV Drug User
4098
Figure 4. Overlap of adult groups at increased risk for AIDS in the United States as of
January 21. 1986 (n = 16,343). *Excludes cases in another category.
435) in 1984.37a This increasing seroprevalence is similar to the epidemic
curve for AIDS in San Francisco. Factors associated with anti-HTLV-IIII
LA V seropositivity in homosexual men were found to be similar to those
associated with AIDS in the two case-control studies: seropositive persons
reported a larger number of homosexual partners and more frequent analreceptive intercourse than did seronegative persons. 30 A statistical association has also been seen between AIDS and seropositivity and "fisting";
however, a proportion of subjects in all studies never engaged in this
practice, making its role less clear. Longitudinal studies show that antibody
prevalence is rising in groups of homosexual men; infection with the
implicated retrovirus is much more common than is AIDS itself, and most
of those exposed have not developed overt AIDS.
Intravenous Drug Use
Coincident with the first published reports of AIDS in homosexual
men were reports of the same syndrome in IV drug users. 45 , 58 These
patients were first diagnosed in early 1980, about 2 years after the first
male homosexual patients. 56 By January 21, 1986, 77% of these patients
had been reported from New York or neighboring northern New Jersey.
About 11% of homosexual patients give a history of IV drug use, providing
a potential mechanism of transmission between the two populations (Fig.
4). The route of transmission is presumed to be by parenteral exposure to
contaminated equipment used for injection. Needle-sharing has been reported to be a risk factor in these patients,36 but the significance of this
practice as a risk factor has not been examined in controlled studies.
Seroepidemiologic studies have demonstrated that 87% of recent IV drug
users enrolled in a detoxification program in New York City had anti-
642
KE"lKETH
G. CASTHO, A"lK YI. HARDY, A"'D
JA~1ES
\\1. CURRAN
HTLV-III/LAV.59 In contrast, much lower rates (10%) of antibody prevalence have been reported in IV drug users in San Francisco, where very
few AIDS cases are in IV drug USerS.58a
Hemophilia
In persons with hemophilia, AIDS was first reported in 1982.8 The
number of such cases has increased significantly over time: the first patient
was diagnosed late in 1981, with an additional 6 in 1982, 11 in 1983, 42 in
1984, and another 72 in 1985. Cases have been reported from 32 different
states. Pooled clotting-factor concentrates with widespread geographic
distribution, primarily factor VIII, are clearly the source of transmission of
AIDS, in the same way as for hepatitis B. Each lot of these concentrates
contains cryoprecipitated material pooled from 2500 to 22,500 individual
donations. The average patient with severe hemophilia uses five to ten
different lots per year. 28a The emergence of anti-HTLV-III/LAV in the
hemophilia population has been dated to shortly after cases of AIDS began
being reported. 26 Anti- HTLV-Ill/LAV was detected in only one of 21
hemophilia A patients in California before 1980. However, by 1984 more
than 85% of these patients had detectable antibodies. Another report
documents detection of anti-LAY in 72% (18 of 25) of asymptomatic persons
with hemophilia A.5:) All had used factor VIII concentrates from 1980 to
1982. In contrast, there was a lower incidence (33%) of HTLV -Ill/LAV
seroconversions in patients with hemophilia B who were treated with factor
IX concentrates.
The high prevalence of anti-HTLV-I1I/LAV and the rapidity with
which seroconversion took place in the hemophilia A population suggest
that factor VIII concentrate is a vehicle for spread of this virus, and that
factor VIII concentrate may have contained HTLV-Ill/LAV during the years
1980-1983. 26,27 Heat treatment of factor VIII concentrate has been shown
to inactivate the AIDS virus. IS Revised recommendations for the treatment
of hemophilia issued by the National Hemophilia Foundation include: use
of cryoprecipitate in factor VIII-deficient newborn infants and children
under 4 years of age and in newly identified patients never treated with
factor VIII concentrates; use of fresh frozen plasma in factor IX-deficient
patients in the same categories; use of desmopressin whenever possible in
patients with mild to moderate hemophilia A; and considering use of heattreated factor concentrates in patients who do not meet the above conditions. 48
Blood Transfusions
Additional evidence for blood-borne transmission of AIDS came with
the reporting of probable transfusion-associated cases to the CDC. 1, 12, 39
Transfusion-associated cases were defined for surveillance purposes as AIDS
patients meeting the criteria for adult or pediatric AIDS, having a history
of blood transfusion within 7 years prior to diagnosis, having abnormal
immunologic studies, and having no evidence to suggest that the patient
was a member of a group at risk for AIDS. As of January 1986, 295 such
cases had been reported, of whom 263 were adults and 32 were children.
The ages of the adults ranged from 14 to 86 years (median, 57 years), and
AIDS:
EPIDEYlIOLOGY AND RISK FACTORS FOR TRANSYlISSION
643
the ages of the children ranged from 4 to 96 months (median, 12 months).
Twenty per cent of the cases were from New York and 22% from California;
the rest were scattered over other states. In general, this geographic
distribution parallels that of adult AIDS cases. The male-to-female ratio in
adults was 1.6:1; in children, it was 2.2:1.
The time interval between transfusion and diagnosis of AIDS ranged
from 5 to 62 months (median 28 months) in adults and from 4 to 46 months
(median 14 months) in children. Since most of the pediatric transfusionassociated AIDS occurred in newborn infants, this difference between
adults and newborn infants may be due to the relative immunologic
immaturity of children, resulting in a shorter incubation period. The first
eight cases of transfusion-associated AIDS were diagnosed in 1982, with 35
cases in 1983, 80 cases in 1984, and 139 cases in 1985. The patients had
first received transfusions in 1978, with increasing numbers from 1979 to
1982. Cases with longer incubation periods in patients who had received
transfusions in these years may yet be reported. In adults the transfusion
was usually associated with surgery (49%), primarily cardiac (27%), with
26% having medical reasons. In contrast, 67% of transfusions in children
were for medical reasons. An opportunistic infection was the primary
manifestation of AIDS; P. carinii pneumonia was the most common such
infection (76%).
In investigations of the donors to these transfusion-associated cases, a
"high-risk" donor has been identified in nearly every case. 25. 51a A "highrisk" donor was defined as a person in an AIDS risk group and/or with
persistently abnormal T-helper:T-suppressor cell ratios. Of the 53 "highrisk" donors found in 48 completed investigations, only nine developed
AIDS; an additional nine developed diffuse generalized lymphadenopathy
(part of the broader spectrum of AIDS-associated disease; see article by
Abrams, page 693) and the rest have been asymptomatic. Implicated blood
components included packed red cells, fresh frozen plasma, platelets, and
whole blood, but no single blood component was found to be associated
with a markedly higher risk of AIDS virus transmission than the others.
The discovery of HTLV-IIIILAV and the development of tests for
detecting both the presence of virus and antibodies to this agent has
permitted the identification of asymptomatic carriers. 28 Lymphocyte cultures were evaluated for HTL V-Ill/LAV in 22 of the 24 completed investigations: specimens obtained an average of 28 months (range, 12 to 52
months) after blood donation were virus-positive for 91 % (20 of 22) of the
completed evaluations. At the time of examination, 68% (15 of 22) of the
virus-positive donors remained healthy, two had been diagnosed with
AIDS, and five had generalized lymphadenopathy. In addition, the isolation
of HTLV -Ill/LAV from both donors and recipients in six of the investigations
has further strengthened the etiologic role of HTLV -III/LA V in AIDS. The
study of these transfusion-associated cases has provided important information regarding the natural history of AIDS. Besides confirming that
blood can transmit AIDS, we have learned that the disease has a long
incubation period, and that asymptomatic persons may transmit the disease.
Recommendations for preventing transmission of the disease were
issued by the U. S. Public Health Service in March 1983,14 with subsequent
644
KENNETH
C. CASTRO, ANN ,\1. HARDY, AND JAYlES W. CL'RRAN
specific guidelines being issued by the Food and Drug Administration.
These recommendations have been implemented by the major blood service
organizations and are aimed at discouraging blood and plasma donation by
persons at an increased risk for AIDS. Donated blood will be tested for
anti-HTLV-IIIILAV to supplement these prevention measures.
Heterosexual Transmission
Reports of AIDS from Zaire and Rwanda also implicate heterosexual
transmission as an important mode of spread of this disease in those
countries. 52. 60 In the United States, AIDS has been reported among
heterosexual partners of IV drug abusers, bisexual men, Haitians, hemophiliacs, and partners of other persons at risk for developing AIDSY· 35
Eighty-six per cent of these patients have been residents of New York,
New Jersey, California, and Florida. Twenty-six per cent of men reported
to the CDC who had no risk factors for AIDS gave a history of sexual
contact with female prostitutes. 19 Most lived in New York City, where the
largest number of cases in female IV drug users has been reported. Further
evidence of HTLV -Ill/LAV transmission through heterosexual contact
comes from a study of 25 heterosexual partners of 21 patients with AIDS
and four patients with AIDS-related conditions. 34 Forty-one per cent of the
sex partners (9 of 22) had anti-HTLV-III/LAV antibodies; one of these
heterosexual partners developed AIDS and three others had AIDS-related
conditions. All 21 patients with AIDS and four patients with AIDS-related
conditions had detectable anti-HTLV-IIIILAV. Specific risk factors for
heterosexual transmission of AIDS have not been conclusively identified.
Controlled studies are in progress to explore the potential role of multiple
sex partners and exposure to prostitutes in heterosexual AIDS transmission.
Other Factors
Approximately 6% of AIDS diagnosed in adults occurs in persons who
cannot be classified into one of the previously described groups. This
includes 399 persons born in Haiti or central Africa, for whom risk factors
for HT LV-1111 LAV infection were not identified. The first cases of AIDS in
Haitian-born immigrants without other risk factors were diagnosed in 1980. 9
This characterized a distinct group with increased incidence of AIDS. 33
Most had entered this country after 1977. Ninety-seven per cent of these
patients are residents of Florida, New Jersey, and New York. Eight-four
per cent are male and 16% are female. P. carinii pneumonia and other
opportunistic infections are more prevalent than Kaposi's sarcoma in these
patients.
AIDS has also been well documented in Haiti. 51 Reports from an
epidemiologic study of AIDS in Haiti indicate that, of 93 male patients,
36% gave a history of bisexuality, 5% had received blood transfusions, and
58% had no identified risk factors. 50 Of 35 Haitian women with AIDS, 40%
gave a history of blood transfusions, 6% were heterosexual partners of
persons at risk for AIDS, and 54% had no identified risk factors. In a casecontrol study of the AIDS patients without known risks, significant differences were reported: AIDS patients were more likely to have received
injections from nonmedical personnel than were controls; and both male
AIDS:
EPIDE\1l0LOCY AI\O RISK FACTOHS FOH THANS\IlSSI0N
645
and female patients were more likely to have had multiple sex partners.'50
Factors underlying the occurrence of AIDS in Haitians living in the United
States have recently been described in a case-control study conducted in
New York and Miami. J Haitian men with AIDS differed significantly from
controls in that they were more likely to report a history of previous
gonorrhea and sexual contact with prostitutes. Among women, the variable
most significantly associated with disease was having been offered money
for sexual favors. In conclusion, risk factors for Haitians may well be the
same as in other groups, and heterosexual transmission is likely to be more
important because of a higher prevalence of AIDS in predominantly
heterosexual men and women. The much higher incidence of AIDS in
recent Haitian entrants (post-1977) is consistent with the hypothesis that
AIDS and HTLV-IlI/LAV infection is relatively new as an important public
health problem in Haiti as well as the United States.
An epidemiologic analysis of the first 136 noncharacteristic AIDS cases
reported in the United States revealed that information regarding risk
factors was incomplete for most (65%) of these patients. However, because
many of these patients were similar with regard to age, race, and area of
residence to populations recognized to be at increased risk for AIDS (for
example, IV drug users and heterosexual partners of persons at risk for
AIDS), some may belong to previously recognized risk groups. 23
Surveillance for AIDS and HTLV-IIIILAV infection in health-care
workers has been undertaken. To date, none of the reported cascs of AIDS
in health-care workers can be linked to a specific occupational exposure. In
the United States, prospective evaluations of health workers with documented parenteral exposure to blood and body fluids of patients with AIDS
have only identified four persons with anti- HTL V-IlI/LA V. 16, 21 22b, 61a In
none of these persons was a pre-exposure serum sample available to date
the onset of infection. However, one nurse in London reportedly developed
anti-HTLV-III 49 days after an accidental needlestick injury while she drew
blood from an AIDS patient. J9 Available data suggest that occupational
transmission of AIDS and HTLV -I III LAV infection will remain uncommon.
CONCLUSIONS
Epidemiologic and laboratory observations suggest that HTLV-Ill/LAV
is transmitted through intimate sexual contact or through parenteral contact
with blood or blood products. It also appears likely that this retrovirus
produces a spectrum of disease ranging from subclinical to fatal. Research
for effective therapy and a vaccine for the AIDS virus has an extremely
high priority. In the interim, a better understanding of the epidemiology
of AIDS will aid in designing better prevention strategies. Current recommendations for prevention of AIDS virus transmission have focused on
risk-reduction practices ll , 14, 20, 22c and attempts to decrease blood-borne
transmission. 14, 20, 48 Health-care workers and others should familiarize
themselves with, and follow, the recommended precautions when handling
specimens, secretions, and excretions of persons known to be infected with
HTLV-Ill/LA V. 22c
646
KENNETH
G.
CASTRO, ANN
M.
HARDY, AND .TAMES
W.
CURRAN
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Possible transmission by means of blood products. Lancet, 1:956-958, 1983.
2. Auerbach, D. M., Darrow, W. W., Jaffe, H. W., et a!.: Cluster of cases of the acquired
immune deficiency syndrome: Patients linked by sexual contact. Am. J. 1\led., 76:487492, 1984.
3. Barre-Sinoussi, F., Chermann, J. c., Rey, F., et al.: Isolation of a T-Iymphotropic
retrovirus from a patient at risk for acquired immune deficiency syndrome (AIDS).
Science, 220:868-871, 1983.
4. Castro, K. G., Fischl, M. A., Landesman, S. H., et a!.: Risk factors for AIDS among
Haitians in the United States. In International Conference on Acquired Immunodeficiency Syndrome (AIDS). Atlanta, Georgia, 1985, session U.
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648
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(Dr. Curran)
AIDS Program
Center for Infectious Diseases
Centers for Disease Control
1600 Clifton Road, N. E.
BUilding 6-288
Atlanta, CA 30333