ai dịch hộ tôi bài trên được không,đặc biệt quan tâm đến cum từ:antibodies is now 20 days less ,
đó là điều rất đáng chú ý,một cở thể bình thường thì 20 ngày là sẽ xuất hiện kháng thể,thử nghĩ mà xem nếu H xâm nhập vào cơ thể anh thì sau 20 ngày cơ thể anh chắc chắn sẽ sinh ra kháng thể chống lại H đó,và tui cũng nghĩ vậy
chẳng lẽ tài liệu của CDC lại viết sai,em xin cop toan bộ tài liệu đó cho các bác tham khảo
http://www.cdc.gov/mmwr/PDF/RR/RR4502.pdf
U.S. Public Health Service Guidelines for Testing and
Counseling Blood and Plasma Donors for Human
Immunodeficiency Virus Type 1 Antigen
Summary
The Public Health Service (PHS) has recommended a multifaceted approach
to blood safety in the United States that includes stringent donor selection practices
and the use of screening tests. Blood donations in the United States have
been screened for antibody to human immunodeficiency virus type 1 (HIV-1)
since March 1985 and type 2 (HIV-2) since June 1992. An estimated one in
450,000 to one in 660,000 donations per year (i.e.,18–27 donations) are infectious
for HIV but are not detected by currently available screening tests. Because
maintaining a safe blood supply is a public health priority, the Food and Drug
Administration (FDA) recommended in August 1995 that all donated blood and
plasma also be screened for HIV-1 p24 antigen, effective within 3 months of licensure
of a test labeled for such use. Donor screening for p24 antigen is
expected to reduce the number of otherwise undetected infectious donations by
approximately 25% per year.
Routine testing for p24 antigen in settings other than blood and plasma centers
as a method for diagnosing HIV infection is discouraged because the
estimated average time from detection of p24 antigen to detection of HIV antibody
is 6 days, and not all recently infected persons have detectable levels of
p24 antigen. Among children
³18 months of age and adults, diagnostic testing for HIV infection, including confirmatory testing, should routinely be performed
with FDA-licensed assays for antibodies to HIV-1; p24-antigen tests alone should
not be used for diagnosing HIV infection.
This report provides PHS guidelines for a) interpreting p24-antigen–assay
results, b) counseling and follow-up of blood donors who have positive or indeterminate
p24-antigen–test results, and c) using p24-antigen testing in settings
other than blood banks.
INTRODUCTION
In the United States, the implementation of antibody testing in 1985 of all donated
blood for human immunodeficiency virus type 1 (HIV-1) resulted in a substantial decrease
in the transmission of HIV through blood transfusions (1,2 ). To further
decrease the risk for transmission of HIV by transfusion, the testing of all blood
donations with a combination antibody test for HIV-1 and HIV type-2 (HIV-2) was implemented
by June 1992.
The risk for HIV transmission by transfusion of screened blood is minimal. Nearly
all cases of transfusion-associated HIV transmission are now caused by blood
donated during the infectious window period (i.e., when recently infected donors
are infectious but have not yet developed detectable levels of HIV antibody). When
whole-virus–lysate enzyme immunosorbent assays (EIAs) were used to screen blood
donations from 1985 through 1990, the average length of the window period was
45 days (95% confidence interval [CI]=34–55 days) (3 ). The average window period of
the most sensitive contemporary recombinant protein-based EIA for HIV-1 and HIV-2
antibodies is now 20 days less (4 ), yielding an average infectious window period of
25 days (95% CI=9–41 days) (5 ).
The increased sensitivity of contemporary HIV-antibody EIAs, improved donor interviewing
about behaviors associated with risk for HIV infection, and deferral of
donors who test positive for HIV, hepatitis, human T-cell leukemia virus type 1 (HTLV-I),
or syphilis have considerably improved the safety of the U.S. blood supply. In 1993,
only approximately six per 100,000 blood donations collected by the American Red
Cross tested positive for HIV antibody (6 ). In addition, only an estimated one in
450,000 to one in 660,000 donations per year (i.e., 18–27 donations) were infectious for
HIV but were not detected by current screening tests (5 ).
During the acute period of infection, tests for p24 antigen can detect HIV infection
earlier than antibody tests. P24 antigen, the core structural protein of HIV, is detectable
2–3 weeks after HIV infection during the initial burst of virus replication associated
with high levels of viremia (7,8 ). During this time, the blood of infected persons is
highly infectious, and tests for p24 antigen are usually positive (9–11 ). On average,
p24 antigen is detected an estimated 6 days before antibody tests become positive
(4,9 ). When antibodies to HIV become detectable, p24 antigen is often no longer detectable
because of antigen-antibody complexing and viral clearance (9–11 ).
In August 1995, the Food and Drug Administration (FDA) recommended that all
blood and plasma donations be screened for p24 antigen, effective within 3 months of
licensure of a test labeled for such use (12 ). FDA recommended p24 screening as an
additional safety measure because a) recent studies indicated that p24 screening reduces
the infectious window period (4 ), b) implementation of p24-antigen testing had
become logistically feasible for mass screening, and c) such testing would reduce the
risk for HIV infection for persons who receive donated blood or blood products.
Among the 12 million annual blood donations in the United States, p24-antigen
screening is expected to detect four to six infectious donations that would not be identified
by other screening tests. If each of these units were divided into an average of
1.8 blood components (13 ), antigen testing would result in removal of an estimated
seven to 11 infectious components each year that would otherwise be available for
transfusion. FDA regards donor screening for p24 antigen as an interim measure
pending the availability of technology that would further reduce the risk for HIV transmission
from blood donated during the infectious window period.
This report provides guidelines for a) interpreting p24-antigen–assay results,
b) counseling and follow-up of blood and plasma donors who have positive or indeterminate
antigen-test results, and c) using p24-antigen testing in settings other than
blood banks. These guidelines may be modified when additional information concerning
antigen testing under mass screening conditions is collected and analyzed.
P24-ANTIGEN–TEST ALGORITHM
AND INTERPRETATION OF TEST RESULTS
The p24-antigen screening assay is an EIA performed on serum or plasma.
If the first screening test is nonreactive, the test result is reported as negative
(see Definitions used in interpreting HIV-1 p24-antigen tests according to FDA
