Structured Abstract
Please note: In 2003, the CTF updated its Grades of
Recommendations to include an "I Recommendation" for situations where
insufficient evidence exists to allow a recommendation to be made.
(Formerly, these situations were captured under a "C
Recommendation".) This change is not retroactive, and all
"C Recommendations" made prior to 2003 have not been
reevaluated in light of the new "I" recommendation grade. For a
discussion of these recommendation grades, please link to the 2003 article in
the Canadian Medical Association Journal here.
Screening for HIV Antibody
Prepared by Elaine E.L. Wang, MD, CM, FRCPC, Department of Pediatrics,
University of Toronto
These recommendations were finalized by the Task Force in November
1991
Contents
Objective
To make recommendations about routine screening for the human immunodeficiency
virus (HIV) antibody among general and high risk populations in Canada.
Burden
of Suffering
By October 7, 1991, 5,349 AIDS cases had been reported in Canada, including
63 pediatric cases. Under reporting by up to 20% may result from
efforts to maintain patient confidentiality and the complexity of the reporting
procedure. Behaviours that increase risk of HIV infection include
having many sexual partners, receiving anal intercourse, sharing needles
during injection drug use and receiving blood or blood products prior to
introduction of universal HIV antibody screening by blood banks.
Homosexual or bisexual men, prostitutes, injection drug users, people receiving
blood products between 1978 and 1985, sexual contacts of people with HIV
infection and people from countries with a high HIV prevalence are at high
risk. Of all cases reported in Canada, 78% were associated with homosexual
or bisexual activity only, 1.4% with injection drug use only, and 3.5%
with both. 95% of AIDS cases belonged to an identified risk group.
Options
Routine and targeted screening were considered. Screening measures included
conducting histories of sexual and drug behaviour and laboratory detection
of antibodies (enzyme-linked immunosorbent assay [ELISA] kits), with confirmation
of positive results using Western blot, radioimmunoprecipitation or immunofluorescence
assays. Treatment included zidovudine (AZT), aerosol pentamidine
prophylaxis for Pneumocystis carinii pneumonia, and counselling.
Outcomes
Sensitivity and specificity of screening tests, delayed onset of acquired
immuodeficiency syndrome (AIDS), opportunistic infections, P. carinii
pneumonia, high risk behaviours.
Evidence
MEDLINE was searched to September 1991 using the MeSH headings "HIV antibody
tests", "AIDS" and "sex-education", "sex-counselling", "sex-behaviour",
"attitude", "screening", "truth-disclosure", "counselling" and "patient
education".
Recommendations were graded as:
|
A
|
Good evidence to support the recommendation that the condition
be specifically considered in a PHE. |
|
B
|
Fair evidence to support the recommendation that the condition
be specifically considered in a PHE. |
|
C
|
Poor evidence regarding inclusion or exclusion of the condition
in a PHE, but recommendations may be made on other grounds. |
|
D
|
Fair evidence to support the recommendation that the condition
be specifically excluded from consideration in a PHE. |
|
E
|
Good evidence to support the recommendation that the condition
be specifically excluded from consideration in a PHE. |
Quality of evidence was rated according to 5 levels:
|
I
|
Evidence from at least 1 properly randomized controlled
trial (RCT). |
|
II-1
|
Evidence from well-designed controlled trials without randomization. |
|
II-2
|
Evidence from well-designed cohort or case-control analytic
studies, preferably from more than 1 centre or research group. |
|
II-3
|
Evidence from comparisons between times or places with
or without the intervention. Dramatic results in uncontrolled experiments
could also be included here. |
|
III
|
Opinions of respected authorities, based on clinical experience,
descriptive studies or reports of expert committees. |
Values
The 13-member Task Force of experts in family medicine, geriatric medicine,
pediatrics, psychiatry and epidemiology used an evidence-based method for
evaluating the effectiveness of preventive health care interventions. Recommendations
were not based on cost-effectiveness of options. Patient preferences were
not discussed.
Background papers providing critical appraisal of the evidence and tentative
recommendations prepared by the chapter author were pre-circulated to the
members. Evidence for chapter topics was presented and deliberated upon
in 1- to 2-day meetings, 2 to 3 times per year from November 1992 to January
1994. Consensus was reached on final recommendations.
Benefits,
Harms, and Costs
Sexual histories are routinely obtained by <50% of physicians. Barriers
to obtaining accurate information include worries about self-incrimination,
prejudice, illiteracy, race, ethnic background, language, and socioeconomic
status. Risk factors were identified in <60% of HIV-positive parturient
women. Targeted screening (e.g., in sexually transmitted disease clinics)
has low sensitivity and specificity. Added counselling did not improve
questionnaire sensitivity in identifying seropositive women.
Cohort studies of homosexual men found statistically significant reductions
in risk behaviours of those aware of their seropositive status. Studies
of the effects of counselling persons with hemophilia or those using injection
drugs have shown similar reductions. These studies are limited due to the
specialized populations and difficulties in measuring and validating sexual
behaviour.
ELISA kits are easy to use and inexpensive. They have high sensitivity,
but lower specificity due to cross reactions with other HIV antigen components.
Repeated positive tests must be confirmed with the Western blot, radioimmunoprecipitation
or immunofluorescence assay. Combined sensitivity of the 2 tests is almost
100%. These tests are not accurate for neonates.
Potential adverse effects of screening arise from false positive results
which could lead to discrimination, prejudice, legal prosecution, rejection
and reduced social support, depression and anger and from false negative
results which could lead to treatment delays.
Treatment with AZT delays the onset of AIDS in asymptomatic persons
with CD4 lymphocyte counts of <0.5 x 109. 100 patients would
need to be treated for 1 year to delay the onset of opportunistic infection
in 4 patients. No data are available on survival, quality of life and adverse
effects. No survival difference exists between symptomatic persons given
early vs late AZT, despite a delay in disease onset.
An RCT of aerosol pentamidine prophylaxis reported a 70% risk reduction
for P. carinii pneumonia among asymptomatic patients with CD4 counts
of <0.2 x 109/L, patients with AIDS and patients with advanced
symptomatic HIV infection with no history of P. carinii pneumonia.
Risk of vertical transmission from mother to fetus is about 30%. Maternal
awareness of seropositive status could result in avoidance of procedures
or behaviours that may increase transmission risk, earlier diagnosis of
AIDS-related illnesses and earlier treatment of infected infants.
Recommendations
Recommendation grade [A, B, C, D, E] and level of evidence
[I, II-1, II-2, II-3, III] are indicated after each recommendation. Citations
in support of individual recommendations are identified in the guideline
text.
-
Poor evidence exists to include or exclude, in the PHE of asymptomatic
persons in the general population, history-taking regarding sexual practices
and injection drug use, and counselling [C,
III].
-
Good evidence exists to offer screening with ELISA and confirmatory tests
to asymptomatic persons at high risk [A,
I] (homosexual and bisexual men, prostitutes, injection drug users,
people with sexually transmitted diseases, people who received blood products
between 1978 and 1985, sexual contacts of persons who are HIV-positive,
and persons from countries with a high prevalence of HIV infection). Patients
with seronegative results should be re-tested after 6 months.
-
Poor evidence exists to include or exclude voluntary screening with ELISA
and confirmatory tests of asymptomatic pregnant women [C,
II-2] or asymptomatic persons at low risk [C,
III].
-
Fair evidence exists to include voluntary screening with ELISA and confirmatory
tests of children of women who are HIV-positive [B,
II-2].
Validation
This report was externally peer-reviewed. The U.S. Centers for Disease
Control recommend screening high risk groups. In 1985, they recommended
screening and counselling of women in high-risk groups, and testing of
patients being treated for tuberculosis. The 1989 U.S. Preventive Services
Task Force found fair evidence to recommend screening of high-risk populations
and pregnant women, and insufficient evidence to include or exclude screening
of low risk populations.
Sponsors
The Canadian Task Force on Preventive Health Care
developed this guideline with funding from Health Canada.
Selected
References
Source Document
Link to Full Text of this
review
Link to Summary Table of Recommendations of this review
Link to Selected References list of this review
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