Survival outside the body

Questions regarding the survival of HIV are frequently raised by people who come into contact with spilled body fluids. Fears over the casual transmission of HIV have also led many people to be concerned over the risk of contact with spilled blood, dried blood or other body fluids, even in microscopic quantities.

It is important to bear in mind that whilst HIV may live for some time outside the body, HIV transmission has not been reported as a consequence of contact with spillages of blood, semen or other body fluids, although many healthcare workers do come into contact with HIV-infected body fluids. Nevertheless awareness of the possible persistence of viable HIV in body fluids will encourage observation of infection control procedures.

Laboratory studies which have looked at the survival of HIV have found that:

• HIV is sensitive to high temperatures but not to extreme cold. Experiments have shown that HIV is killed by heat, but temperatures over 60°C are needed to achieve reliable killing of HIV.
• Levels of virus remain relatively stable in blood at room temperature, and HIV may persist for at least a week in dried blood at 4°C. Blood containing HIV used for laboratory experiments is stored at –70°C without any loss of viral activity.^{1 2}
• HIV may survive for up to four weeks in syringes after HIV-infected blood has been drawn up into the syringe and then flushed out.³ A study of blood gathered from more than 800 syringes filled with small amounts of HIV-infected blood and stored for various periods found that HIV could be isolated from 10% of syringes after eleven days where the quantity of blood was less than 2µl, but 53% of syringes where the quantity of blood was 20µl. Longer survival of HIV was also associated with lower storage temperature (less than 4°C); at higher temperatures (27 to 37°C) survival was not detected beyond seven days.
• HIV is very sensitive to changes in alkalinity or acidity – pH level – and pH levels below 7 or above 8 are unsuitable for long-term survival of HIV. One reason why HIV transmission may be less likely in healthy women is due to the acidity of vaginal secretions.^{2 4}
• HIV may survive in dried blood at room temperature for up to five or six days provided that the optimum pH level is maintained; drying of blood does not seem to affect the infectivity of HIV.²
• Sewage is highly unlikely to pose a risk because infectious HIV has never been isolated from faeces or urine.⁵ However, research by Thames Water has shown that HIV can survive for several days in sewage in the laboratory.⁶
• HIV does not survive as long as other viruses in sea water.⁶
• Infectious HIV has been recovered from human corpses between eleven and 16 days after death in bodies stored at the usual mortuary temperature of 2°C. It is unclear how long infectious HIV may persist in corpses left to decay at normal room temperature, but HIV has been cultured from organs stored at 20°C up to 14 days after death. HIV was not detected in significant quantities later than 16 days, implying that buried corpses or those preserved for long periods pose less of a risk to undertakers and pathologists.^{7 8}
• No studies have investigated the survival of HIV in semen outside the body as such, but studies which have sought to culture HIV from semen in the laboratory have often found it difficult to do so, indicating the low quantities often present in semen.

These findings do not take into account factors such as the dose of virus necessary to establish infection (the tissue culture infectious dose) or the chance that the virus will reach target cells assuming that the skin is injured. Just because an individual comes into contact with tiny quantities of HIV in dried blood, it does not follow that infection will occur.

The effect of environmental conditions such as wind, rain etc. is not taken into account in these laboratory-based studies.

Concerns about contact with blood from corpses may be more realistic depending on the quantities of blood present and given the evidence for long-term survival of HIV after death.

A 2003 review in Australia concluded that HIV can survive outside the human body for periods up to several weeks. “Viral survival is influenced by virus titre, volume of blood, ambient temperature, exposure to sunlight and humidity.” ⁹ The review focused on the risk of transmission following injuries with syringes discarded by drug users, and noted that there had been no reported transmissions of either HIV or viral hepatitis in Australia.