Expert: John Locke - 7/23/2010

Question
Hi John
I read your article on the restaurant dish washing practices. I am constantly concerned by my mothers use of a washing container in the kitchen sink.  

She washes all the food in the same bowl and then does not rinse them - I believe they should be rinses to get off the film of dirty water that must still be on them.

But the other day she also used the basin to wash her summer shoes.  I felt ill knowing my children use dishes in her home that have been washed in that.  She said she washes it out with the antibacterial dish washing detergent and that kills the germs.

Do you know of any studies that show that:
1. Dishes should be rinsed off - to remove
a).dirty dish water and
b). the nasty chemicals they contain
2. that antibacterial dishwashing detergent (generic store brought) will not kill all the germs

thanks in advance - sure appreciate your time
le

Answer
Thanks for using AllExperts, and sorry for the delay. I can provide you with various information regarding the effectiveness of dishwashing methods, in particular the effectiveness of dishwashers compared to handwashing. We have to consider a couple of factors first. There is almost no way to achieve complete sterilization--the killing of all bacteria, viruses, fungi, and spores on a surface--with the tools commonly available in a home. It is possible to significantly reduce the bacterial load on these surfaces to a low level, comparable with that of the other surfaces in the surrounding area. It is very difficult to get something much cleaner than the surrounding environment and maintain it that way for a long period of time.

Let's consider a couple of facts. Most commercial dishwashers use a 75 degree Centrigrade thermostat for the highest hot water setting in the wash cycle. This is far beyond what could be tolerated in hand-washing (for comparison, 60 degree C water is 140 degrees Fahrenheit, which is hot enough to scald with only seconds of exposure), but it still is not sufficient for sterilization: the steam cycles in an autoclave--a device made specifically for the sterilization of laboratory instruments--use steam heated to 125 degrees C under several atmospheres of pressure. The temperature of water used in hand-washing alone is not sufficient to achieve sterilization.

There is, however, a standardized mechanism for evaluating the effectiveness of dishwashers in achieving sterilization put out by the NSF (http://www.nsf.org/consumer/residential_appliances/dishwasher.asp?program=Reside...). Dishwashers that meet these standards don't achieve total sterilization but they do significantly reduce the bacterial load on dishes when using the "sanitize" cycle. This is far above what handwashing is able to attain.

Antibacterial soap uses triclosan or alcohol as microbicidal agents to kill bacteria. There is some controversy at present as to whether these soaps are any more effective than regular soap at removing bacteria from surfaces; the three studies referenced below came to differing conclusions on the matter. For more information about any of them, Google the full title and you will find abstracts that summarize the results. There are a few certain conclusions, however: the effect is not incredibly dramatic, whatever exactly it is, and antimicrobial soaps are no more effective against viruses than regular soap. Antibacterial soap, as such, is not a panacea for decontamination.

J.C. Lucet (2002), Hand Contamination Before and After Different Hand Hygiene Techniques: a Randomized Clinical Trial, Journal of Hospital Infection; L.L. Gibson (2002), Quantitative Assessment of Risk Reduction From Hand Washing with Antibacterial Soap, Journal of Applied Microbiology

Aiello AE, Marshall B, Levy SB, Della-Latta P, Lin SX, Larson E. (2005), Antibacterial cleaning products and drug resistance. Emerg Infect Dis., Oct;11(10):1565-70.

Aiello AE, Larson EL, Levy SB. (2007), Consumer antibacterial soaps: effective or just risky? Clin Infect Dis., Sep 1;45 Suppl 2:S137-47.

There is no question that dirt on a surface will prevent it from being adequately cleaned until the dirt is removed. Visible contamination serves as a reservoir for microorganisms, and it can recontaminate a surface that has been cleaned if it is not removed. A similar effect occurs with any film of organic matter or even dish soap: anything that forms a film between the surface of the object being cleaned and the cleaning agent that is being applied to it will prevent microbes from being completely removed from that surface. The review article linked below discusses the problem of sterilization with food processors, finding that pre-washing and rinsing after washing are important steps in the decontamination process. Taken generally, it is important to rinse initially to remove visible dirt, which serves as a reservoir for microorganisms, and to rinse afterward to remove the film that may prevent adequate cleaning.

http://www.ncbi.nlm.nih.gov/pubmed/19539390

If you require any clarification or desire more information, I would be happy to provide it. Good luck.