Experiments 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 (Van Bueren; Tjotta).
• 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 (Abdala). 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 11 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 degrees C); at higher temperatures (27-37 degrees 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 difficult in healthy women is due to the acidity of vaginal secretions (Tjotta; Voeller).
• 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 (Tjotta).
• Sewage is highly unlikely to pose a risk because infectious HIV has never been isolated from faeces or urine (ACDG). However, research by Thames Water has shown that HIV can survive for several days in sewage in the laboratory (Slade).
• HIV does not survive as long as other viruses in sea water (Slade)
• Infectious HIV has been recovered from human corpses between 11 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 (Anon; BMJ; Ball; Nyberg).
• 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 TCID) 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 is more realistic given the quantities of blood present and the evidence for long–term survival of HIV after death. Guidelines have been produced by the Advisory Committee on Dangerous Pathogens (see Infection Control).

References

Abdala N et al. Survival of HIV-1 in syringes. Journal of Acquired Immune Deficiency Syndromes and Human Retrovirology 20: 73-80, 1999.

Advisory Committee on Dangerous Pathogens: HIV – the causative agent of AIDS and related conditions, Dept of Health, 1990.

Anon: BMJ report on Forensic Science International 60: 61–66 on post mortem, 1993.

Ball J et al: Long lasting viability of HIV after patient's death, Lancet 338: 63, 1991.

Nyberg M et al: Isolation of human immunodeficiency virus (HIV) at autopsy one to six days post–mortem, Am J Clin Pathol 94(4): 422–425, 1990.

Slade JS et al: The survival of human immunodeficiency virus in water, sewage and sea water, Water Science and Technology 21(3): 55–59, 1989.

Tjotta E: Survival of HIV–1 activity after disinfection, temperature and pH changes or drying, J Medical Virology 35(4): 223–227, 1991.

Van Bueren: Survival of HIV and inactivation by heat and chemical disinfectants, Eighth Int Conf AIDS, Amsterdam, abstract PoA 2401, 1992.

Voeller B: Heterosexual transmission of HIV, JAMA 267(14): 1917–1919, 1992.