Immunodeficiency Virus 1 - Survival


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Human Immunodeficiency Virus 1


HIV-1 survival in needles and on surfaces and probability of transmission

Survival of the virus is defined as persistence in an infectious state.

Transmission probabilities of infectious virus are very difficult to measure for most modes of transmission because they depend on confirmation of the infected source, HIV-1 viral load, viral tropism, and exposure of the source to antiretroviral therapy.

Although for transfusion risk assessments, an infective dose of HIV-1 is estimated to be 10 viral particles (approx. 20 copies of HIV-1 RNA), this is assumed to be an overly conservative estimate because of high ratio of defective (non-infectious viral particles) to viable HIV-1 particles in vivo (some estimate up to 90-99% of HIV RNA is defective).

The TCID50 (50% tissue culture infective dose) is a relative measure of infectivity which differ from ID50 (50% animal model host infectivity). The ID50 is often given in units of TCID50 and not in RNA copy number. For example, for the chimpanzee model, the ID50 ranges from 4 to 300 TCID50 for various isolates of HIV; however, chimpanzees are relatively resistant to HIV. ID50 values for host adapted viruses are much lower. For example, in pig-tailed macaques, the 50% infective dose of SHIV ranges from 0.1 to 1.0 TCID50.

Parenteral transmission

Parenteral is a route of administration that involves piercing of the skin or mucous membrane, which include contaminated injections, needle sharing in intravenous drug use (IDU), accidental percuteneous injuries (for example, needlestick injury), and blood transfusion.

Injection drug users

In review and meta-analysis Baggaley RF et al. have estimated infection probability for IDU ranging from 0.63% to 2.4%.

In an assay of syringes used to simulate injection drug use, after one day of storage the detectable HIV was reduced by 75-90%. Heating of infected needles prior use would greatly reduce possibility of infection because stability of the virus is reduced by a factor of 10 between 48 and 52°C. Flushing of syringes with water also was shown to greatly reduce virus inoculum and infection probability: one flushing removed competent viral particles in 70% of syringes, two flushings eliminated replicative virus in 95% of syringes.

Contaminated injections

Estimated infectivity per contaminated injection was estimated as 1.9-6.9% based on data from outbreaks in Russia, Romania and Libya.

Accidental percuteneous injury

Based on analysis of 22 studies on needlestick exposures (total 644 injuries), Baggaley RF et al. produced estimate of infection probability ranging from 0.18% to 2.38%. The probability highly depends on needle gauge. Reid S, Juma OA. produced the equation for probability of infection per μL inoculum volume for needlestick injuries:
P = 1.3 x volume (μL) + 0.27
If source patients progressed to AIDS, the probability increases by factor of 1.9. For reference, the average inoculum volume in a needlestick simulation for non-venous (i.e. intramuscular) injection using an 18 gauge syringe is 2.87 μL. In a few experiments that simulated accidental injections and needlestick injuries volume of inoculum ranged from 1.3 to 34 μL.

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HIV-1 survival on surfaces

Many parameters influence the capacity of a virus to survive in the environment, including the concentration of virus, temperature, humidity, and surrounding medium.

Reliability of test results on HIV survival in the environment and assays of disinfectant efficacy are both dependent on means for the detection and quantification of infectious HIV. Techniques that are sensitive and specific but do not measure viral infectivity (such as nucleic acid probes) are not suitable. Early studies used reverse transcriptase (RT) activity for indirect detection of infectious virus. The most common detection method is detection of p24 antigen by commercial ELISA assays but it is not sufficient to prove that the remaining virus is still infectious. In this regards, susceptible tissue cultures challenged with HIV can be assumed to be infected if the level of p24 antigen detected in the culture increases with time. Incubation periods of at least 28 days are required to ensure the absence of HIV in particular culture. Infectious dose of virus in tissue cultures is measured by TCID50, which, as mentioned above, can be much higher than 50% host infectivity (ID50).

For person to be infected by infectious virus that persisted on surface in dried or suspended state, the virus has to be collected, reconstituted and inoculated. The probability of such an event is by itself is very low. However, governmental, academic, commercial research establishments as well as health-care institutions often handle quantities of HIV much greater than those normally encountered by general public.

Neither potable nor recreational waters have been implicated in the transmission of HIV infections. There is no information on the capacity of HIV-1 to survive in food and no epidemiologic evidence to indicate that HIV can spread through this route.

HIV-containing aerosols such as generated in dental practice, in orthopedic surgery, and in laboratories must be regarded as potentially hazardous.

Viral inocula dried on the surface of Petri dishes and kept at room temperature were rapidly inactivated, however, potentially infectious virus could be detected for up to 3-7 days after incubation.

HIV can be inactivated by various intermediate-strength disinfectants such as chlorine compounds, ethanol, and isopropyl alcohol. Alcohols are less effective against HIV than chlorine.

In conclusion, probability of infection of members of general public from environment (food, water, household items, etc.) is extremely low (practically zero). Researchers and medical personnel involved in handling of large amount of HIV-1 containing media must follow Occupational Health and Safety Administration (OSHA) standards and most current CDC guidelines and protocols.

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