Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Blood borne infections

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Bacterial blood borne infection can occur, typically in

the transfusion of blood. Such infections arise from the con-

taminationof the site of transfusion. While information on the

rate of such infections is scarce, the risk of transmission of

bacterial infections via transfusions is thought to be at least

equal to the risk of viral infection. For example, figures from

the United States Food and Drug Administration indicate that

bacterial infections comprise at least 10% of transfusion-

related deaths in the United States each year.

Another route of entry for bacteria are catheters. For

example, it has been estimated that the chances of acquiring a

urinary tract infection (which can subsequently spread to the

blood) rises by up to 10% for each day a hospitalized patient

is catheterized.

While bacteria can be problematic in blood borne infec-

tions, the typical agents of concern in blood borne infections

are protozoaand viruses. The protozoan Trypanosoma brucei

is transmitted to humans by the bite of the tsetse fly. The sub-

sequent infection of the blood and organs of the body produces

sleeping sickness, al illness that still afflicts millions each

year in the underdeveloped world.

With respect to viral blood borne diseases, hepatitisA,

hepatitis C, and the Human Immunodeficiency Virus(HIV; the

cause of acquired immunodeficiencysyndrome) are the focus

of scrutiny in blood donors and in the setting of a hospital.

Exposure to the blood from an infected person or the sharing of

needles among intravenous drug users can transmit these

viruses from person to person. In Canada, the contamination of

donated blood and blood products with the hepatitis viruses

and HIV in the 1980s sickened thousands of people. As a result

the system for blood donation and the monitoring guidelines

for the blood and blood products was completely overhauled.

For example, in the 1980s, monitoring for hepatitis C was in its

infancy (then only a few agencies in the world tested blood for

what was then termed “non-A, non-B hepatitis”). Since then,

definitive tests for the hepatitis C virus at the nucleic acid level

have been developed and put into routine use.

Within the past 20 years, emerging diseases such the

lethal fever and tissue destruction caused by the Ebola virus

have been important blood borne threats. These so-called hem-

orrhagic feversmay have become more prominent because of

human encroachment onto formerly wild regions, particularly

in Africa.

Health care workers are particularly at risk of acquiring

a blood borne infection. Open wounds present an opportunity

for blood to splatter on a cut or scratch of a doctor or nurse.

Also, the use of needles presents a risk of accidental puncture

of the skin to doctors, nurses and even to custodial workers

responsible for collecting the debris of hospital care.

Thin section electron micrograph of Ebola virus.

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