80% Multi-purpose Disinfectants Showed Limited Efficacy in Killing Test Bacteria and Virus in a Short Period of Time Diluted Bleach and Alcohol Preparation Would be an Effective and Economical Option When Used Appropriately

14 January 2021
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80% Multi-purpose Disinfectants Showed Limited Efficacy in Killing Test Bacteria and Virus in a Short Period of Time Diluted Bleach and Alcohol Preparation Would be  an Effective and Economical Option When Used Appropriately

As the pandemic persists, a variety of multi-purpose disinfecting products have cropped up, claiming to be able to disinfect the environment, objects and hands without pre-dilution, making it convenient to use. However, the Consumer Council has tested 15 models of multi-purpose disinfectants and found that the bactericidal and virucidal performance varied. 80% (12) of the models, including 9 models claiming to have a 99.9% kill rate and reduction of viral infectivity, performed not as well as 75% alcohol-based preparation or/and diluted bleach solution containing 500ppm available chlorine (equivalent to diluting household bleach containing 5.25% sodium hypochlorite with water in a 1:99 ratio). From the test results, the Council reminds consumers that diluted bleach solution, as compared with disinfectant sprays, is a relatively more economical, consistently effective and reliable choice for general disinfection.

Also, many consumers have the habit of spraying themselves and their clothing all over after returning indoors in order to kill the virus. The Council reminds consumers that chloride compounds or other chemical substances may cause irritation or undesirable reactions and thus should not be sprayed directly on the human body. On the other hand, the effectiveness of inappropriate fogging of disinfectant in the living environment is doubtful, and it may also contaminate food and beverages, increasing the risk of accidentally consuming the disinfectant or their residues. In fact, simple practices such as maintaining good personal hygiene, washing hands frequently and using alcohol-based handrubs appropriately, are more effective at reducing viral infection than improper use of novel disinfectant sprays.

15 models of multi-purpose disinfectants were tested, including 9 models with claimed hypochlorous acid concentrations ranging from 50ppm to 210ppm (commonly known as “hypochlorous acid water”); 3 were labelled as chlorine dioxide or oxychlorine compound products; the remaining 3 only listed plant extracts as the active ingredient. Test items included the performance in killing test bacteria and inactivating the test virus, as well as determination of available chlorine, pH value, and assessment of the stability of the product.

No Definite Correlation Between Bactericidal and Virucidal Efficacies    Available Chlorine Concentration and Product Stability are Key Factors

The test results showed that models of hypochlorous acid generally have a better performance at inactivating the test virus and boast a decent bactericidal efficacy as well. However, product performance would be affected by other factors such as the formulation stability, pH value and storage condition when used in real-life situations.

Amongst the 9 disinfectant sprays labelled with hypochlorous acid, the available chlorine concentration measured immediately upon opening of the samples ranged from undetected to 230mg/L, with the actual value of 3 models lower than their claims, including 2 models which claimed to contain 220ppm and 1 model which claimed to have 50ppm, but its available chlorine concentration was lower than the detection limit. Of the 3 models labelled as containing chlorine dioxide or oxychlorine compounds, 2 were detected to contain available chlorine at concentrations of 660mg/L and 160mg/L respectively. Available chlorine was not found in the remaining 3 models labelled as containing plant extracts.

The test also simulated the usage of these products in a real-life daily scenario. During the test period, 2ml of disinfectant were sprayed from each model each day, then each model was tested for their available chlorine concentration and pH value in 3 stages, namely when the sample was first opened, then respectively on the 7th and 14th day after simulated use and storage in the test environment. The results showed that the stability of the 3 hypochlorous acid models were generally mediocre, with the available chlorine concentrations of the models dropping by 9.1% to 20.0% after storing till the 14th day. The pH value of 1 model showed a significant change from pH6.1 to pH4.3.

All 15 multi-purpose disinfectants claimed to have bactericidal properties.  Among the 12 models labelled as having a bacterial kill rate as high as 99.9% or 100%, 4 models performed less effective than their claims. The test was conducted with reference to the European standard EN1276:2019 and compared the product performance at 20°C when placed in the test environment with a specific amount of interfering substances for 1 minute, then compared their efficacy of killing Escherichia coli K12 and Staphylococcus aureus. Test results revealed that 8 models were able to eliminate both models of test bacteria, with a kill rate of over 99.999%. The remaining 7 models showed drastic disparity in their performance of killing the 2 test bacteria, with the Escherichia coli K12 kill rate ranging from 14.286% to 72.347%, and the kill rate of Staphylococcus aureus ranging from 11.111% to 98.956%. Amongst these, 2 chlorine dioxide-based models had a worse bactericidal performance, with a disappointing kill rate of less than 28% against both test bacteria.

The results also revealed, however, that consumers should not estimate a product’s efficacy in inactivating viruses within a short period simply by referencing their bactericidal performance. Amongst the 15 test models, 9 that claimed to eliminate 99.9% to 99.999% viruses failed to meet their claim in virucidal efficacy in the test. The test was conducted with reference to the European standard EN14476:2013+A2:2019 and compared their performance at 20°C when placed in an environment with a specific concentration of interfering substances for 1 minute, then tested for their efficacy in reducing the viral infectivity of a harder-to-kill test virus — Adenovirus type 5. Test results revealed that for 13 models, the reduction of viral infectivity of the test virus ranged from 0% to 96.20%, of which the poorest performing model showed 0% efficacy against the virus and was also the poorest performing model in the bactericidal test. 2 other models which had over 99.999% bactericidal efficacy, on the other hand, only achieved 18.72% and 0% in the reduction of viral infectivity. Only 2 models in the test showed a relatively more satisfactory virucidal performance, reducing the viral infectivity by over 99.99% and 99.95% respectively.

75% Alcohol-based Preparation and 1:99 Diluted Bleach    Showed Good Bactericidal and Virucidal Efficacy

Aside from comparing the bactericidal efficacy and reduction of viral infectivity of various models of disinfectant sprays, the test also applied the same test methods and conditions to test 75% alcohol-based preparation (prepared with reference to the formulation recommended by the World Health Organization) and diluted bleach solution containing 500ppm available chlorine (equivalent to diluting household bleach containing 5.25% sodium hypochlorite with water in a 1:99 ratio). The results showed that these 2 models of commonly used disinfectants both achieved a kill rate of 99.999% for the test bacteria, and reduction of viral infectivity of 87.98% and 99.83% respectively. To summarise the test results, only 3 hypochlorous acid-based models (20%) achieved comparable performance to alcohol-based preparation and diluted bleach. However, disinfectant sprays are generally costlier, averaging $88 to $798 per bottle/set, equivalent to around $0.27 to $0.99 per millilitre. Based on the Council’s previous report on disinfecting alcohol published last April, the price per millilitre for disinfecting alcohol ranged from around $0.04 to $0.5 which was cheaper in average. Alcohol-based preparation and diluted bleach solution are cost-effective options sufficient for disinfecting hands and general environments respectively.

Inspection of the labelling information of 15 models revealed that 3 models which claimed to contain plant extracts did not list out the detailed information of the ingredients; 4 models labelled as containing hypochlorous acid or chlorine dioxide also did not clearly state the concentration of the relevant ingredient; only 3 models mentioned that the product requires 30 seconds to 15 minutes to take effect for killing bacteria and disinfection purposes; 2 models did not include any information on the effective period. The Council reminds product suppliers to ensure clear information on the product labels to prevent potential misuse or inappropriate usage of the products due to unclear instructions, which may ultimately affect the efficacy or even increase the risk of virus infection.

The Consumer Council reminds consumers that disinfectant sprays are not invincible anti-pandemic products. Basic and effective prevention measures should not be neglected, such as wearing face masks correctly, washing hands regularly, and always maintaining personal and environmental hygiene. Consumers should pay heed to the following should they decide to purchase and use novel disinfectant sprays:

  • It is possible to come into contact with more than 1 type of bacteria or virus in daily life. The amount of disinfectant spray used, application method, spraying distance and even the period of use may all affect the disinfection effect. Sufficient amount and time are of essence;
  • In a real-life environment, objects may often have dirt on the surface. It is important to clean the surface to ensure proper disinfection;
  • Never spray disinfectants containing chlorine or other toxic chemical substances directly at the human body to avoid irritating the eyes and skin. If inhaled, it may even cause bronchial spasm, nausea or vomiting. Discontinue use immediately if allergic reaction develops after contact;
  • Avoid spraying disinfectants in liberally amounts and extensively in living spaces and interiors. Ensure sufficient distance from food and beverages when applying the disinfectant to avoid the risk of intaking droplets or residue by accident;
  • Hypochlorous acid is easily affected by light and heat. Store it away from heat sources and sunlight. It is recommended to purchase freshly manufactured batches and use as soon as possible after the bottle has been opened.

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