and the Chain of Infection
HIV is a relatively fragile virus. It is
not spread by casual contact. It is not easy to "catch"; it
must be acquired. HIV is considered to be a fragile virus
when exposed to air and room temperatures. Hepatitis B (HBV)
and hepatitis C (HCV) are both considered "stronger" viruses
that can remain infectious for a longer period of time. When
these viruses are outside the human body, much depends on
environmental factors such as heat, cold, exposure to oxygen,
etc.). HBV and HCV will be discussed later in this course.
The Chain of Infection provides a
model for understanding how any infection is spread. All of
the components below must be present for an infection to occur.
The pathogenic microorganism is the microorganism
that causes infection such as bacteria, viruses, fungi and
parasites. There must be a sufficient dose of the organism,
that is enough concentration and amount of the organism to
The reservoir is the place where microorganisms live,
such as in humans and animals, in soils, food, plants, air
or water. The reservoir must meet the needs of the pathogen
in order for the pathogen to survive and multiply.
The means of escape are how the microorganism leaves
The mode of transmission is how the microorganism
moves from place to place.
The means of entry is how the micro-organism enters
the host. There must be an adequate number of organisms to
The host susceptibility is the person who may become
All of these components together are considered to be the
"chain of infection". In the healthcare setting, all of these
factors come into play in the spread or the control of infection.
There are effective strategies of infection control that will
prevent infection transmission by interrupting one or more
links in the chain of infection (CDC, 2007).
The following is how the chain of infection relates to HIV/AIDS:
- The pathogenic microorganism is the human immune deficiency
virus, or HIV. A sufficient dose, or concentration and amount,
of HIV must be present for infection to occur.
- The reservoir is blood or body fluids of the "source"
patient; anyone with the virus can be an HIV source.
- The means of escape are how the blood or body fluids
of the source patient exit the source patient. This includes
infected blood, semen, vaginal secretions or breast milk.
- Mode of transmission is through direct contact with infected
blood or body fluids noted above.
- The means of entry is through the non-intact skin that
can occur through unprotected sex, injecting drug use, and
rarely splashing onto mucous membranes.
- Host susceptibility is the person who may now become infected
Mr. R. is a middle-aged, married, Caucasian, male
computer salesman who was transported to the ED after
being found unresponsive in his apartment by a neighbor.
Following a thorough exam the provider suspected a
possible drug overdose, which was confirmed when a
urine drug screen was positive for cocaine. Once stabilized,
the staff offered him an HIV test. Mr. R. adamantly
refused the test saying that he did not have any risk
factors. The provider suspected this was not true
and proceeded to perform a social history. Eventually,
the provider was able to solicit answers that indicate
Mr. R. is at risk for HIV: he has been sexually active
since high school and has not always used condoms;
while he is primarily heterosexual and has been married
for almost 15 years, he has occasionally located men
on the internet that he met for dates; he has never
used intravenous drugs, but does share straws when
using cocaine; he was incarcerated for assault when
he was younger, and while in jail had used a common
needle to give himself a tattoo.
Mr. R. thought that since he had only used drugs
with people he knew and had sex with healthy looking
men he did not have risk factors for HIV. He also
thought that someone would have found out he was HIV
positive during a recent hospital admission when he
had labs drawn daily prior to and after major surgery.
The provider convinced Mr. R. that he should have
an HIV test based on the results of his assessment.
He provided him with education focusing on routes
of transmission and appropriate barrier use. He explained
the risk of having unprotected sexual relations and
the fact that you cannot tell someone has HIV/AIDS
by the way they look. The test results were negative,
and the provider stressed the importance of retesting
if he engaged in more high risk behaviors.
To date, there have been less than a dozen known cases of
HIV transmission that have occurred in household settings
in the U.S. and other countries. Reports of these cases have
been thoroughly investigated by the CDC. The researchers determined
that the transmissions were caused by sharing a razor contaminated
with infected blood, the exposure of infected blood to cuts
and broken skin, and possibly deep kissing involving a couple
who both had bleeding gums and poor dental hygiene. It is
important to remember that these cases were extremely unusual.
Sensible precautions with bleeding wounds and cuts and not
sharing personal hygiene items would have prevented these
cases of infection.
There are also isolated cases of transmission from healthcare
workers to patients.
How HIV is NOT Transmitted
No cases of HIV transmission have been linked to sharing
computers, food, telephones, paper, water fountains, swimming
pools, bathrooms, desks, office furniture, toilet seats, showers,
tools, equipment, coffee pots or eating facilities However,
personal items, which may be contaminated with blood, including
but not limited to razors, toothbrushes and sex toys, should
not be shared.
There have been no cases of HIV transmission by children
playing, eating, sleeping, kissing and hugging.
Biting poses very little risk of HIV transmission. The possibility
only exists if the person who is biting and the person who
is bitten have an exchange of blood (such as through bleeding
gums or open sores in the mouth.) Bites may transmit other
infections, and should be treated immediately by thoroughly
washing the bitten skin with soap and warm water, and disinfecting
with antibiotic skin ointment.
Ms. P. decided to have an HIV test after finding out
that an old boyfriend had HIV. She was shocked to
hear the news at first and went to the testing clinic
knowing there was a chance of infection, but she was
confident that she was in good health overall, and
had not been sick or had any unusual symptoms. She
had dated this boyfriend for about 3 months at least
six years ago but they just didn't "click." Eventually,
they went their own ways and began dating other people.
Several years ago she moved to a nearby city and changed
jobs. She only found out about his illness by chance
when she happened to meet a mutual friend at an art
When the test results came back positive she could
not believe it at first. Then, all at once, she began
to think about men she had been involved with since.
How many had she infected?
Ms. P. was given an appointment at an HIV treatment
center to discuss the need for antiretroviral therapy.
Before beginning therapy, the provider ordered a genotype
test to identify any possible viral resistance she
might have. When the results were back, she was informed
that she had been infected with a strain of virus
that was multi-drug resistant (MDR). In other words,
many of the commonly used medications for HIV would
not provide effective treatment. The provider also
explained that infection with HIV that is MDR is more
common than many people realize. In one recent study
in NY City, 10% of people newly diagnosed with HIV
had MDR, and more than 25% had at least some resistance
(Shet et al., 12th CROI, 2005). Medications would
need to be carefully selected to provide the best
treatment possible. Even so, infection with a strain
of MDR HIV makes progression to AIDS and death more
Continue to Part 2. HIV
Transmission and Infection Control, Con't.