Coronavirus has made us all more aware of the potentially contaminated surfaces on objects we once didn’t worry about touching and sharing. That includes the balls used in sports for exercise and entertainment.
Because a sports ball is usually passed from one player to the next, it could potentially act as a vector that spreads the SARS-CoV-2 coronavirus. A ball’s surface can become contaminated by virus particles in respiratory droplets expelled by infected people who show no symptoms (asymptomatic carriers) via breathing or sweating during physical activity, for instance.
Science has some good news about sports balls: they seem to be relatively easy to disinfect, according to a study from a mainly-British multidisciplinary group led by cancer researcher Justin Stebbing at Imperial College London and fund manager Peter Davies, non-executive chairman of Oxford Sciences Innovation.
The new study involved testing sports balls after they had been ‘infected’ with SARS-CoV-2. Their contaminated surfaces were disinfected using common cleaning wipes and then tested for the presence of virus particles.
Several experiments were carried out using various concentrations of virus and disinfectants, such as cloths containing 70% isopropyl alcohol and ‘wet-wipes’ similar to moist toilet tissue. The balls were those used in cricket, tennis, golf and football (soccer), covered by materials like leather, felt or plastic. A cricket balls is similar to a baseball and possibly the most-handled in sport.
One experiment used a solution of SARS-CoV-2 diluted by 50%. The solution was smeared onto the balls, which were rolled around a grass field for 5 minutes to mimic having been played with, then wiped thoroughly with an alcohol-based cloth for 2 minutes, rinsed with water and left to dry at room temperature for 2 hours — a procedure replicating how a ball might be disinfected after a game — while the dilution might represent mixing infectious respiratory droplets with sweat. No virus was detected following that experiment.
In another experiment, undiluted virus was pipetted directly onto the surface of a cricket ball, mimicking the effect of a cough, spitting or sneezing into a player’s hands. Virus was detected on the ball’s surface 1 hour later, but when the solution was diluted by 50%, the virus could only be detected 5 minutes later. That result illustrates the importance of disinfecting sports equipment after use.
Surprisingly, one experiment showed that the cloth used to clean the surface of a ball doesn’t matter much: regardless of whether a wet-wipe or dry paper tissue was used, no virus was detected from a 50% diluted solution. That suggests that in real-world settings, where droplets have dried-up and any virus particles are wiped away, the ball is unlikely to be ‘infectious’.
Little is known about environmental contamination by SARS-CoV-2, and we still don’t know how long it lasts on surfaces. According to a review led by Günter Kampf of the Institute of Hygiene and Environmental Medicine in Germany, coronaviruses persist on inanimate surfaces for between 2 hours to over a month — depending on conditions such as temperature and humidity.
Although the new study focused on sports balls, its results can be compared to previous research. An early study under laboratory conditions found that SARS-CoV-2 remains stable on metals and plastic for three days. Such materials are used to make objects with a large surface area, like furniture, so testing the materials used in small balls provides an interesting contrast.
Overall, the results suggest that the concentration of virus affects whether it is detected later, and that you might prevent a ball from becoming a vector for transmission with relatively little cleaning.
As the study’s authors conclude, “Sports objects can only harbour inactivated SARS-CoV-2 under specific, directly transferred conditions, but wiping […] removes all detectable viral traces. This has helpful implications to sporting events.”
The implications will be reassuring for those of us who play with our balls on a regular basis. That group includes not only amateur sportsmen and people who use them in physical activity (like an exercise ball at a gym) but also professional athletes who are constantly handling balls that have been touched by others.
At a time when any news about Covid-19 is almost always depressing, being entertained by sports and science stories is probably good for mental health.