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Children's plastic toys can 'harbour viruses for hours'

07 July 2016

This laboratory study aimed to assess virus survival on a plastic toy at 22C and two different humidity levels – 40% (similar to indoor levels) and 60%.

Researchers used a virus called bacteriophage Φ6, which is harmless for humans. It acts as a useful "surrogate virus" for research, as its structure is similar to common causes of viral infection, such as the influenza virus.

The study found that viral survival was significantly less at the lower humidity – at two hours, virus survival had reduced by 99.9%. At high humidity, it took 24 hours to reduce by 99%.

Children's toys – particularly shared ones like in daycare centres and hospitals – have often been implicated in spreading infection during outbreaks. However, this study can't provide all the answers. For example, it can't inform us about the survival of other bacteria and viruses (e.g. tummy bugs spread hand-to-mouth), or whether viral survival may be the same on other surfaces.

What is probably most useful is the standard hygiene measure of ensuring that your child washes their hands regularly, after playing, after using the toilet and before eating.

Employees in settings where toys are likely to be shared should also be aware of the importance of regularly cleaning the toys.
Where did the story come from?

The study was carried out by researchers from Georgia State University, Atlanta, US. It was funded by a grant from the university, and the authors declare no conflict of interest. The study was published in the peer-reviewed Pediatric Infectious Disease Journal.

The Mail article may suggest that this study has directly shown that viruses on plastic toys lead to infection, which isn't the case. As is so often the case, its headline verges on scaremongering. This study had a valuable purpose, but its results weren't conclusive.

These criticisms aside, the body of the article was largely accurate and informative.
What kind of research was this?

This was a laboratory study aiming to assess the survival of viruses on plastic toys in different environmental conditions.

The researchers explain how toys may transmit viruses to children, particularly shared toys in daycare centres, hospitals and doctors' waiting rooms. They go on to say how many cross-sectional studies have assessed the presence of viral DNA or RNA, but it's difficult to tell whether actual enveloped viruses are present and how long they survive.

This study aimed to assess an enveloped virus that infects and replicates within Pseudomonas bacteria – a virus called bacteriophage Φ6, which has similar characteristics to influenza. Enveloped viruses have a protective shell, so they can survive longer on external environments, such as objects and surfaces.

The researchers looked at its survival on non-porous plastic toys in different conditions.
What did the research involve?

The researchers incubated the Pseudomonas bacteria with the bacteriophage Φ6 virus in the lab. They cut up a disinfected plastic toy (a squeaking frog) into 1cm2 pieces and put the culture onto them.

They then incubated for 24 hours, some at 22C and 40% humidity, and others at 22C and 60% humidity. They assessed virus survival over the 24 hours.
What were the basic results?

Over 24 hours, there was a 99% reduction (2log10) in the number of infective viruses when incubated at 60% humidity. The number had already halved by 8 hours (1log10).

There was a significantly increased rate of decline at 40% humidity. There was a 3log10 decline at two hours, and 6.8log10 decline by 10 hours.

Log10 is a reference to measurements on the logarithmic (log) scale, which is a useful method of talking about very large numbers and very small numbers at the same time (in this case, viral load).
How did the researchers interpret the results?

The researchers conclude: "a lipid-enveloped virus [a virus with a protective shell] can survive on the surface of a nonporous children's toy for hours at indoor temperature and relative humidity levels, and the relative humidity level affects how rapid the inactivation is".

This laboratory research assessed the survival of a single type of bacteria-infecting virus on a plastic toy at 22C and two different humidity levels.

The bacteriophage Φ6 virus was chosen to be representative of influenza and other enveloped viruses, and indicated how they would survive under the same conditions. Certain characteristics of the bacteriophage, though, make it easier to study than the actual viruses.

The 40% humidity was meant to be typical of indoor environments. The researchers found that even at this humidity, it may take up to two hours to achieve a 99.9% reduction in levels of infectious virus – similar to previous findings about the rate of inactivation of the flu virus on non-porous surfaces. High humidity was associated with even longer viral survival.

However, this study is limited as it doesn't address many other issues, such as:

viral decline at other temperatures – combined with these and other humidity levels
survival of other types of non-respiratory viruses – or bacteria – on plastic toys, such as gastrointestinal viruses and bacteria that are spread hand-to-mouth, like norovirus or E.coli bacteria; whether the viral levels detected here at different time-points would directly lead to infection in a child if they were to touch the object is unknown
levels of viruses and bacteria on environmental surfaces all around us – for example doors and door handles, tables, work surfaces, taps, etc – all of which children would equally come into contact with
the effect of disinfecting or cleaning the items

Toys and children's play equipment has previously been linked to transmission of viruses during outbreaks. In environments such as nurseries, daycare, hospitals or surgeries where toys are shared, regular cleaning and/or disinfection of the items may be beneficial in helping to limit the spread of infection.

However, what is probably most useful is ensuring that your child washes their hands regularly, after playing, after using the toilet and before eating.