Hi,Rick! I have two questions: 1. In your answers you often say that the
virus does not survive more than a few minutes outside the body. I have
read a paper by P.J.G.Butler. In this paper, he says that HIV is not
unstable under normal enviormental conditions as is some times assumed.
Infectivity has been shown to persist for up to seven days following air
drying and for more than 15 days at 23-27c (and>11 days at 37c) in an
aquaous state. Wnich one is correct? 2. If HIV is not transmitted
through every casual contact, why there are 3% of patients haven't
"identified risk"? How are they infected? Thank you very much!
Hi. Thank you for your question.
There has been a lot of misunderstanding (and misinterpretation) of the
scientific data looking at survival of the HIV virus outside the body.
Studies that looked at HIV survival, used concentrations of HIV at least
100,000 times higher than concentrations normally found in nature. Using
these extremely high concentrations of HIV was used out of necessity,
because of scientific and technical limitations. In studies using these
extremely high concentrations, HIV was able to survive for 1-3 days after
drying, but inactivation of the virus was extremely rapid (90-99% within
several hours). Now, does this mean that HIV at normal concentrations will
survive for up to 3 days? No! Remember that these are concentrations of HIV
that are at least 100,000 times higher than that found in nature. When we
extrapolate this data down to natural concentrations of HIV, we can determine
that HIV can only live for several minutes outside the body. If HIV were to
be able to survive outside the body for many hours or days (at natural
concentrations), we would have seen cases of HIV transmission through casual
contact. In the over 15 years that we have been studying HIV transmission,
we have never seen any cases of transmission through casual contact
In regard to cases of AIDS where risk has not been identified, let me tell
you the "statistic behind the statistic". I'll use USA AIDS statistics as an
example. Out of almost 550,000 cases of AIDS in the USA, in only 893 cases,
were we not able to determine the source of infection (as of 30 June, 1996).
Of these cases, this includes heterosexual contact with a person not known
to be HIV positive, persons who chose not to disclose their risk factors for
HIV (which is not an unusual occurrence), and persons with possible
occupational exposures. These 893 persons included:
Individuals having a history of other Sexually Transmitted Diseases
(STD's) indicating high risk sexual exposures,
Individuals with Hepatitis infections (Hepatitis B and C share similar
routes of transmission as HIV),
Individuals having a history of non-IV drug use (alcohol and other
judgement affecting drugs, has a well-known link to HIV, due to behavior
changes while under the influence of these drugs) and,
Individuals having occupational exposures to blood or body fluids.
So out of the literally thousands of cases of AIDS, in only a small number of
cases were we not able to determine a definitive source of infection. But
many of these individuals did have known risk behaviors, and markers of risky
exposures. There is no evidence that anybody has been infected through
casual contact worldwide. It's very easy to misinterpret statistics when it
comes to how a person became infected. For example, if a person refuses to
cooperate with health officials or doctors, is lost to follow-up if they move
out of the area, or if they die before we can determine their risk, these
individuals would be classified as having an unknown risk factor for HIV
infection. This doesn't mean that HIV is being transmitted in a new way.
What it does mean is that we were unable to collect the information.
Statistics like these can be very easily misinterpreted.
In summary, it's important to understand that statistics and scientific
reports can be easily misinterpreted, if a person only tells part of the
data, rather than all of it. I hope this has cleared up some of the
If you have any further questions, please feel free to call the Centers for Disease Control at 1.800.232.4636 (Nationwide).