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!
Mr. Sowadsky's Response:
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 worldwide.
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:
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 misunderstanding.
If you have any further questions, please call the Centers for Disease Control at 1-800-342-2437 (Nationwide).
Rick Sowadsky MSPH CDS
NV AIDS Hotline Coordinator