May 25, 2000 May 22, 2000 -- Common activities such as using a telephone, turning the kitchen faucet on and off, or wringing out a sponge may result in infection with disease agents such as Shigella, Salmonella, the cold virus and other agents, say researchers from the University of Arizona. They report their results today at the 100th General Meeting of the American Society for Microbiology.
The degree of transfer of Serratia rubidea (a bacterium similar to Shigella and E. coli, agents of diarrheal disease) and PRD-1 (a bacterial virus similar to a human virus) from common articles in the home to the hand was studied. Transfer efficiency was found to be particularly high for faucet handles (28% and 34%) and phone receivers (39% and 66%). Further studies showed that 34% of the Serratia rubidea as well as the PRD-1 virus could be transferred from a contaminated fingertip to the lower lip.
These results were coupled with the published information regarding the infective dose (number of microbes required to cause an infection) and levels of disease-causing microbes called pathogens found in human fluids such as stool and nasal secretions (snot).
The research was performed by Dr. Patricia Rusin, Dr. Charles Gerba and Sheri Maxwell at the University of Arizona, Tucson. The work was funded by Procter and Gamble.
Examples of several possible scenarios of disease transmission from common articles to humans may be drawn from these results. A telephone receiver could easily serve to transmit disease. Large numbers of Salmonella (a common bacterial cause of diarrhea) may be found in the stool of an infected person. Hence, if even only a tiny amount of stool were transferred from an infected person's contaminated hand to a telephone receiver, the next user could have 107,104 Salmonella cells on the fingertip. If this were placed in the mouth, the person would receive a dose of 36,383 cells which could easily result in disease.
We know that viruses can survive (remain infectious) for hours to days on a hard surface, infectious doses are often very low and large numbers are often found in human fluids such as nasal drainage and stools. Hence, if a virus such as the rotavirus (a diarrheal virus) were on the surface of a telephone receiver, infectious doses could easily be transferred to persons using the telephone. For example, if a telephone receiver were contaminated with a low concentration of rotavirus agent (e.g. 10,000 viruses) 6,580 of these would be transferred to the hand during normal use of the telephone with 211 of them found on the fingertip. Our results show that 72 viruses could be ingested by the user which would very likely result in disease.
Faucet handles have also been shown to be highly contaminated sites, especially in the kitchen. We know that high levels of the cold virus may be found in the nasal secretions (snot) of infected persons and the infectious dose is very very low. We also know that this virus can survive for several hours on surfaces such as faucet handles. Hence, if an infected person deposited even a small amount of infected nasal secretion unto a kitchen faucet handle, 1,037 viruses could be deposited unto the hand of another family member who touched the faucet handle. If this person then places the fingertip in the mouth, nose or eye, 11 viruses would most likely be transferred into the opening. This would, again, be quite likely to result in infection.
Previous studies by the authors show that the common household sponge may contain 320,000,000 opportunistic bacterial pathogens. Based on a 0.0009% transfer efficiency to the hand, 2,912 bacteria would be transferred to the hand. Assuming 3.2% (93) of these bacteria are distributed on the fingertip, then 34% or 32 cells would be transferred into the mouth. This means that if pathogenic bacteria were in the sponge, such as E. coli, in high numbers, infectious doses could be transferred to the mouth.
This work shows that everyday activities in a contaminated household or workplace could easily result in the transmission of disease. Disease can probably be transmitted in the home more often than these studies suggest because many of these articles are used repeatedly in the home. For instance, a homemaker will handle a contaminated kitchen sponge many times during the day multiplying the probability of disease transmission.
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