The Effectiveness of Bleach in the Prevention of Hepatitis C Transmission - Final Report

3. Summary of the Data on the Use of Bleach as a Disinfectant

In an effort to slow transmission of bloodborne pathogens among people who use injection drugs, harm reduction programs have tried to educate injection drug users about the dangers of sharing needles and other injecting equipment. These programs encourage the use of new needles for every injection or, when new equipment is not available, to use bleach to clean needles before each use. However, the effectiveness of bleach disinfection has not been adequately examined.

Liquid bleach is sodium hypochlorite (NaOCl) in a water-based solution. Most household bleach contains 5.25% NaOCl (range 3% to 6%)⁴⁰, with available chlorine of approximately 50,000 parts per million (ppm)¹⁸.

Studies investigating the use of disinfectants for cleaning needles and syringes used by people who inject drugs have focused primarily on the ability of disinfectants and viricides to inactivate HIV. The goal was to find a method of disinfection that was effective, convenient and inexpensive. Bleach was deemed the best agent, as it met five important criteria: it is relatively non-toxic when injected in small quantities; it is a commonly used disinfectant for environmental surfaces; the disinfectant effect is quick; it is easily available; and it is inexpensive and convenient^41,42. Bleach is distributed by needle/syringe exchange programs, often in conjunction with sterile needles and condoms⁴³.

a) HCV Disinfection with Bleach

In vitro studies have shown that bleach is effective for inactivating many pathogens, including HIV and hepatitis B44-46. However, relatively little is known about the inactivation of HCV by chemical germicides¹⁸. The lack of an in-vitro cultivation system for HCV limits the ability to investigate the efficacy of disinfection. Published information comes mainly from experiments in which the integrity of viral particles, antigens, nucleic acid and/or enzymes is used as a measure of the presence or absence of infectious virus. Such tests may show viral presence, but do not necessarily answer questions of infectivity¹⁸. Even polymerase chain reaction (PCR) detection methods cannot distinguish between infectious and inactivated virus⁴⁷.

To address this challenge, some researchers have turned to animal models.

Unfortunately, the only truly appropriate animal model is the chimpanzee. Given their endangered status chimpanzee studies are both ethically difficult and very expensive¹⁸. More recently, other viruses including the bovine diarrhea virus (BVDV) have been used as surrogates for HCV^18,48.

The current challenge of determining true infectivity limits our ability to evaluate appropriate dilution and exposure times. A 1:10 dilution of domestic bleach is commonly recommended for clean up of blood spills, and this concentration should be adequate to deal with HCV (and HBV) in blood¹⁸, although supportive evidence is lacking. However, blood remaining in a syringe poses different challenges than surface blood spills. The risks of transmission from an improperly cleaned and disinfected syringe are much higher than from traces of blood left on an outside surface. Studies have shown that undiluted bleach requires shorter exposure times than diluted bleach to be effective against HIV-1. It may also be more effective in the presence of residual blood in the syringe⁴⁹. Presumably, the same would be true against HCV.

b) Factors Affecting HCV Inactivation

As with any disinfectant, there are factors that reduce bleach's effectiveness against HCV. These include the amount of organic material, e.g., fresh, dried or clotted blood, left in or on the equipment ('soil load'), how long the blood has been sitting in the syringe, the length of time bleach is in contact with the equipment, the "freshness" of the bleach and whether or not the bleach is used properly^42,50.

Studies have shown that contact time and soil load are the two most significant of these. Disinfection with an effective compound for an inadequate time may not succeed in inactivating sufficient amounts of the pathogen to render it non-infective. Likewise, residual organic compounds, such as blood or infected tissue, can significantly impair any disinfectant's ability to inactivate HCV, HBV, HIV or other pathogens. Therefore, even highly effective chemicals can fail to properly inactivate HCV in the absence of proper cleaning (removal of residual blood) of the devices that are being disinfected¹⁸.

The stability of bleach also affects its effectiveness as a disinfectant for injection drug users. For example, dilution and storage in direct sunlight are known to reduce bleach stability and available free chlorine for disinfection^44,51.

Current laboratory methods limit our ability to determine the effectiveness of bleach for inactivating HCV. In the absence of a simple in vitro cultivation system it is difficult for researchers to determine if changes in viruses' physical appearance, reduction of viral load and/or viral inhibition of host cell binding represent loss of infectivity. As well, laboratory test conditions often bear little resemblance to field use. Contact times between the virus and the test product are often too long to be realistic for field use. And the 'soil load' in test virus suspension may not be reflective of difficult-to-deal-with body fluids, such as blood¹⁸.

c) Studies on the Efficacy of Bleach for Disinfecting   Injecting Equipment

There have been a limited number of studies that attempted to demonstrate the effectiveness of bleach or related germicides against HCV. Kapadia et al. examined associations between bleach use and HCV seroconversion using a nested case-control^c design. Compared to participants reporting no bleach use, they found that those who reported using bleach all the time had an odds ratio^d for HCV seroconversion of 0.35 and those reporting bleach use less than all the time had an odds ratio of 0.7652.   However, this study did not have sufficient power to determine if these results were statistically significant.

Agolini et al. showed that another chlorine-based compound, sodium dichloroisocyanurate (NaDCC), at a dilution resulting in 2500ppm chlorine inhibited the binding of HCV to host cells, which might imply reduced infectivity. This inhibition reached a maximum of just 91.7% after a contact time of 10 minutes⁵³. As this chlorine compound is less sensitive than sodium hypochlorite (bleach) to inactivation by organic substances, household bleach might be even less effective.

In another study, Charrel et al. used molecular tests to evaluate the efficacy of two disinfectants for inactivating HCV: a 2% glutaraldehyde solution and a sodium hypochlorite with potassium permanganate and monosodium phosphate solution. Although the sodium hypochlorite-based disinfectant was able to inactivate HCV-positive serum, it did so only at concentrations greater than 90% (4500 parts/million active chlorine) after a contact time of 10 minutes⁵⁴.

Given its disinfectant properties and its success against other pathogens, including hepatitis B, bleach may be effective for disinfecting HCV-infected needles and other IDU equipment. However, the available literature is not conclusive.

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Notes

• Kapadia et al. matched 78 cases (IDU HCV seroconverters) with 390 persistently HCV seronegative injection drug users, all between 18 and 30 years of age. Up to five controls were matched to each case on gender, race/ethnicity, recent (within last six months) injection, date of study entry and length of follow-up.
• 'Odds Ratio' (OR) is the chance that an event will happen (e.g., infection/ seroconversion) compared to the chance that it will not happen (e.g., an odds ratio for group A vs. group B. of 4.0 means group A has 400% (four times) the chance of the event happening).

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