Contamination of Supermarket Shopping Carts

Contamination of Supermarket Shopping Carts

Who would have thought that grocery shopping was such a risky activity? 
For those who partake in the activity of grocery shopping the humble cart holds many perils. First is the one with the stuck wheel that makes it impossible to control to the point that it feels as if it has a mind of its own and seems to go everywhere but straight. Then there is the game of dodgems as fellow shoppers try, but never seem to be successful, in avoiding bumping into each other. 
Then there is the tailgater shopper who almost breaks your ankle when they run into you from the back in a fit of cart-rage. More common these days, half-empty residues of free-sample pots littering the inside baskets with residues wiped on the handles in the absence of tissues. A further interesting feature of shopping carts is that they are the most highly contaminated surface encountered in public settings in a list that includes washrooms, drinking fountains, reusable grocery bags and even mobile phones. Indeed, it almost appears that cart handles are a magnet for microbes. The underlying reasons for poor sanitary status of shopping cart handles is due to be handled by multiple people coupled with infrequent sanitation.
So apart from shopping, what does a cart carry?
The first notable study linked to assessing the sanitary status of shopping carts was performed by Reynolds et al (2005) and later by Gerba & Maxwell (2012) with Morris (2010) also contributing to the area. The general conclusion of the studies was that the handles of shopping carts have a high microbial loading (>6 log cfu) that includes populations of the fecal indicator E. coli (50- 92% incidence).  Of more concern is the recovery of pathogens such as Shiga Toxin producing Escherichia coli (STEC), Salmonella and Staphylococcus aureus (including MRSA). The prevalence on carts vary from 0.2 -13% thereby representing a significant public health risk. It should also be noted that the likelihood of additional pathogens such as norovirus and other parasites likely exists but has yet to be confirmed.
What are the potential sources of contamination?
Contamination of shopping cart handles can occur when shoppers handle raw meat that could carry pathogens on the packaging surface or through contact with exudate that leaks out of packs. Among other sources of contamination are from shoppers themselves. Specifically, if a person suffering a cold sneezes into their hands and contacts the cart handle, then the virus would be transferred. In other instances, if shoppers don’t wash their hands after visiting the washroom or changing their youngsters diper, then a broad range of pathogens, including Clostridium difficile, could be transferred to handles. The question if microbes can grow on the handles of carts is debatable but possible if food residues are wiped on the surface. One would also suspect temperature and moisture would be factors in determining the extent of microbial growth.
Who is at risk?
One of the highest risk groups of contracting pathogens from handles are the young children due to intermit contact with the handle as they sit in the cart. The elderly, pregnant and those taking immune-suppressive drugs are additional groups at risk. The pathogen type is also likely significant given that norovirus, protozoan, STEC and C. difficile have low infectious doses.  
With healthy people there may be a low risk of contracting illness but it is possible to bring pathogens into the home environment that can lead to health issues down the road.
So is the risk real?
To answer this question we decided to run a test whereby fluorescent dye (Glowgerm) was deposited on the handle of a shopping cart before I went around doing my weekly shop. I looked for traces of fluorescent dye on my hands and food items following the shopping trip. Sure enough, the dye had transferred from the handle to my hands then onto the food items that included fresh produce, meat, whey cheese and bread (see video insert). We also took ATP swabs of handles of 20 random selected shopping carts and found counts in the range of 1100 – 3400 RLU which is higher than what would be defined as a sanitary surface (300 RLU). The experiment confirmed that the handles of carts harbor microbial populations and exchange between persons and products occurs.
So what can be done to enhance sanitary status of shopping carts?
In response to the study by Reynolds et al (2005) many retailers provided disinfection wipes and/or hand rubs for shoppers to disinfect cart handles. However, like relics from a lost civilization, the wipes disappeared and rub dispensers left empty. Other initiatives tested are copper handles along with washers. Although both approaches proved effective at reducing contamination neither have been adopted by retailers due to the additional costs incurred. This may be short sited as preventing illness is more cost effective than treating conditions. Therefore, if retailers will not provide wipes or hand rubs then shoppers should consider taking their own to give the cart handles a wipe-down before use. Nevertheless, one hopes that retailers will step up and consider the health of their customers. 
Gerna, C. P. and Maxwell, S. (2012). Bacterial contamination of shopping carts and approaches to control. Food Prot Trends 32; 747-749.
Morris , M. A (2010). Molecular detection of fecal-bacterial contamination on grocery store shopping cart handles within the Sacramento region. MSc thesis. California State University (
Reynolds, K.A., P. M. Watt, S. A. Boone, and C. P. Gerba. (2005). Occurrence of bacteria and biochemical markers on public surfaces.  Int. J. Environ. Health Res. 15:225-234

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Date published: 22/09/2017
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