By Siouxsie Wiles 03/10/2016


A story about a baby catching a life-threatening infection from a shopping trolley has made the headlines. So what was this life threatening infection, and was the trolley really to blame?

This story originally appeared in the DailyMail Australia which saw Vivienne Wardrop’s Facebook post warning other parents about shopping trolley hygiene. Her 10 month old son is currently recovering from what clearly looks like a serious illness, which his mum has narrowed down to him catching after being sat in a shopping trolley (or a cart, for any Americans reading this..). The article says the youngster had “adenovirus, rotavirus, salmonella and meningitis” so what are all those, and was the shopping trolley to blame?

Salmonella and salmonellosis

Salmonella is a family of bacteria that is divided into 2 species, S. enterica and S. bongori. S. bongori is found in cold-blooded animals, especially reptiles, but S. enterica (of which there are over 2000 different types) is found in warm-blooded animals all around the world. S. enterica can cause typhoid fever and paratyphoid fever as well as a form of food poisoning called Salmonellosis with fever, vomiting and diarrhoea. Salmonella infections can be caught by eating or handling contaminated food (including meat, cheese, eggs, milk, fruit and veggies*) or by contact with contaminated surfaces or people.

Infected people and animals shed the bacteria in their poop, and can continue to shed the bacteria for months after they have recovered from an infection. Symptoms usually appear 6-72 hours after infection, and those most at risk of severe disease are young children, the elderly, and people with compromised immune systems. According to the Ministry for Primary IndustriesSalmonella is the second most common cause of bacterial food-borne illness in New Zealand, with around 1000 cases a year [pdf].

Adenovirus, rotavirus and meningitis

Adenovirus is a virus that rarely causes severe illness although it can be a problem for infants and people with weakened immune systems. It most commonly causes respiratory symptoms, but can also cause diarrhoea and fever, usually 2-14 days after infection. The virus is spread though close contact, coughing and sneezing and touching contaminated surfaces. This is another one that can be shed by people in their poop, again for months after they’ve recovered.

Rotavirus is a really common virus which causes vomiting and diarrhoea, again spread though contaminated poop, with symptoms appearing 1-2 days after infection. 90% of NZ kids will have had a rotavirus infection by the time they are 3, and a vaccine against this virus is now part of the childhood immunisation programme in New Zealand. Meningitis is inflammation of the protective membranes covering the brain and spinal cord (the meninges), and can be caused by a host of different bacteria and viruses. In this case, the meningitis could have been caused by the Salmonella infection.

It’s possible that the mention of rotavirus and adenovirus are red herrings. They could have been viruses picked up by the tests but that weren’t actually causing any symptoms (perhaps being shed by the baby after previously being infected). Alternatively, the baby could have caught these infections after the Salmonellosis because of his weakened immune system.

So was it the shopping trolley?!

Maybe, maybe not. The mother is adamant that after ruling everything out, it must have been the shopping trolley that was the source of her son’s illness, but in reality, people are very bad at remembering important things like what they have eaten and who they have been in contact with. The Salmonellosis could just have easily been caught by contact with an infected but asymptomatic person or animal, or their poop. But it is not beyond the realms of possibility that the trolley seat/handle was contaminated with traces of Salmonella-containing bird poop, or the poop of a previous occupant.

Searching the medical literature I was able to find one study that has looked at bacteria contamination of shopping baskets (1). Carried out in Japan, the authors grew 56 isolates of Staphylococcus aureus from 760 shopping basket handles.  But it’s not just shopping baskets. There have also been plenty of studies showing just how “contaminated” our whole environment is. For example, a study of over 1000 surfaces from a range of environments, including shops, airports, restaurants and offices, found that 5-10% of the surfaces tested positive for coliforms, the bacteria associated with poop (2). Interestingly, the authors identified children’s playground equipment as a priority for more research into potential exposure to infectious diseases.

While this case has clearly been awful for the family involved, its likely to be a fairly rare event, so I’m not sure we should all become terrified of shopping trolleys as a result. In reality, bacteria and viruses are EVERYWHERE. Rather than attempting to decontaminate every surface we touch (and its not clear how effective a quick once over with a disinfectant wipe actually is…), the best way to avoid diseases like Salmonellosis is to practice good hand hygiene, admittedly a tall order for young kids.

*Earlier this year, hundreds of people in Australia became infected after eating contaminated pre-packaged salad.

References:

  1. Mizumachi E, Kato F, Hisatsune J, Tsuruda K, Uehara Y, Seo H, Sugai M (2011). Clonal distribution of enterotoxigenic Staphylococcus aureus on handles of handheld shopping baskets in supermarkets. J Appl Microbiol. 110(2):562-7.
  2. Reynolds KA, Watt PM, Boone SA, Gerba CP (2005). Occurrence of bacteria and biochemical markers on public surfaces. Int J Environ Health Res. 15(3):225-34.