BMJ 2014;349:g7185 doi: 10.1136/bmj.g7185 (Published 16 December 2014) Page 1 of 7 Research BMJ: first published as 10.1136/bmj.g7185 on 16 December 2014. Downloaded from RESEARCH CHRISTMAS 2014: MEDIA STUDIES Transmissibility of the Ice Bucket Challenge among globally influential celebrities: retrospective cohort study OPEN ACCESS Michael Y Ni clinical assistant professor, Brandford H Y Chan research officer, Gabriel M Leung chair professor, Eric H Y Lau assistant professor, Herbert Pang assistant professor School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China Abstract Introduction Objectives To estimate the transmissibility of the Ice Bucket Challenge The Ice Bucket Challenge, a campaign to raise awareness and among globally influential celebrities and to identify associated risk 1 factors. support for people with amyotrophic lateral sclerosis, is widely http://www.bmj.com/ recognised to have gone socially viral. Although there are Design Retrospective cohort study. variations to the trial, participants typically complete the Setting Social media (YouTube, Facebook, Twitter, Instagram). challenge (they are doused in ice water or make a donation) and 2 Participants David Beckham, Cristiano Ronaldo, Benedict Cumberbatch, nominate three others to undertake it. As of 1 September 2014, Stephen Hawking, Mark Zuckerberg, Oprah Winfrey, Homer Simpson, more than 17 million videos related to the Ice Bucket Challenge and Kermit the Frog were defined as index cases. We included contacts were shared on Facebook alone, and these were viewed more 3 up to the fifth generation seeded from each index case and enrolled a than 10 billion times by more than 440 million people. Socially on 28 September 2021 by guest. Protected copyright. total of 99 participants into the cohort. viral phenomena include videos that are made popular by sharing on the internet, and a video is said to have gone viral if it spreads Main outcome measures Basic reproduction number R , serial interval 0 rapidly as a result of frequent sharing.4 5 However, the infectious of accepting the challenge, and odds ratios of associated risk factors disease modelling framework has seldom been used to quantify based on fully observed nomination chains; R is a measure of 0 the transmissibility of such socially viral phenomena.6 The most transmissibility and is defined as the number of secondary cases commonly used metric of transmissibility is the basic generated by a single index in a fully susceptible population. Serial reproduction number (R ), defined as the number of secondary interval is the duration between onset of a primary case and onset of its 0 cases generated by a single index in a fully susceptible secondary cases. 7 population. The value of R0 is a major determinant of the size Results Based on the empirical data and assuming a branching process of an epidemic, and an infection can only be self sustaining if we estimated a mean R0 of 1.43 (95% confidence interval 1.23 to 1.65) R0 is greater than 1. The R0 also provides a measure of the effort and a mean serial interval for accepting the challenge of 2.1 days required to control the epidemic.7 8 We estimated the (median 1 day). Higher log (base 10) net worth of the participants was transmissibility of the Ice Bucket Challenge among globally positively associated with transmission (odds ratio 1.63, 95% confidence influential celebrities and identified the associated risk factors. interval 1.06 to 2.50), adjusting for age and sex. Conclusions The Ice Bucket Challenge was moderately transmissible Methods among a group of globally influential celebrities, in the range of the pandemic A/H1N1 2009 influenza. The challenge was more likely to be Participants spread by richer celebrities, perhaps in part reflecting greater social We considered globally influential celebrities who had influence. undertaken the Ice Bucket Challenge to be eligible for inclusion. Correspondence to: M Y Ni [email protected] Extra material supplied by the author (see http://www.bmj.com/content/349/bmj.g7185?tab=related#datasupp) Tree structure showing nominations associated with Cristiano Ronaldo Tree structure showing nominations associated with Oprah Winfrey No commercial reuse: See rights and reprints http://www.bmj.com/permissions Subscribe: http://www.bmj.com/subscribe BMJ 2014;349:g7185 doi: 10.1136/bmj.g7185 (Published 16 December 2014) Page 2 of 7 RESEARCH Global influence was defined by the criteria: listed in TIME Results BMJ: first published as 10.1136/bmj.g7185 on 16 December 2014. Downloaded from 100: The Most Influential People in the World9 or TIME: Great People of the 20th Century,10 or having at least five million view Eight index cases complied with the inclusion criteria. In total counts for the Ice Bucket Challenge on YouTube. Among the we included 91 nominees up to the fifth generation seeded from small pool of potentially eligible participants we arbitrarily each index case, and a total of 99 participants were enrolled into chose David Beckham, Cristiano Ronaldo, Benedict the cohort. Overall, 24.2% of participants had zero successful Cumberbatch, Stephen Hawking, Mark Zuckerberg, Oprah nominations, 32.3% had one, 26.3% had two, and 17.2% had Winfrey, Homer Simpson, and Kermit the Frog as index cases three. Twelve (4.9%) out of the 247 nominations had already (table 1⇓). We also included successful nominations up to the participated in the Ice Bucket Challenge and were therefore fifth generation seeded from each index case. “immune” from future participation. Among those observed were a Nobel laureate, a university vice chancellor, “heart Data collection throbs”, and Muppets (both the actors and the puppets). Among the index cases, Mark Zuckerberg’s nomination chain produced We completed a marathon viewing of 145 Ice Bucket Challenges the most successful number of contacts (total of 41) up to the up to 13 September 2014. For each case we recorded the age, fifth generation (figure⇓). No serious adverse events arising sex, occupation, net worth, popularity (proxied by number of from the Ice Bucket Challenge act were observed in this series, likes on Facebook and number of Twitter followers), number but adverse events have been reported elsewhere,16 including of successful nominations, and total number of nominations. falls, head injuries, a temporomandibular joint dislocation, cuts, We obtained personal details of the celebrities from Wikipedia and at least one fatality. We estimated the measure of and specialised websites, although the validity of such 11 transmissibility, R0, to be 1.43 (95% confidence interval 1.23 information cannot be reliably ascertained. Wikipedia has been to 1.65) and a mean serial interval of accepting the challenge used in previous studies12 13 and its comparative accuracy has 14 of 2.1 days (median 1 day). We excluded Homer Simpson and been reported. From verified accounts we obtained the number Kermit the Frog in the regression models because of difficulty of Facebook likes and Twitter followers. Where these were not in ascertaining their personal characteristics. Participants with available, we used the unofficial accounts with the most likes a higher log (base 10) net worth were more likely to spread the or followers. We excluded unofficial accounts with fewer than Ice Bucket challenge (odds ratio 1.63, 95% confidence interval 1000 likes or followers. 1.06 to 2.50), adjusted for age and sex. One unit change on a We traced contacts through Google, YouTube, Facebook, log (base 10) scale is equivalent to a 10-fold change in net worth. Twitter, and Instagram. Online written or video responses by We tested the proportional odds assumption for the regression the nominated contacts were used to determine completion of model and found no indication of violation. Age, sex, the challenge. If we found no evidence for a response to the occupation, number of Facebook likes, or number of Twitter challenge on social media, it was assumed that the contact had followers were not associated with transmissibility (table 2⇓). http://www.bmj.com/ declined. We included all successful contacts. Two of the Data were missing for 24.0% of net worth, 15.6% of Facebook authors (MYN, BHYC) independently collected the data. After likes, and 13.5% of Twitter followers. Sensitivity analysis by the fifth generation seeded from each index case they stopped multiple imputation yielded similar results (not shown). data collection owing to investigator fatigue. We did not seek previous consent from participants as they presumably Discussion participated in the Ice Bucket Challenge without coercion, albeit with varying degrees of peer and social pressure. The Ice Bucket Challenge—a campaign to raise awareness and support for people with amyotrophic lateral sclerosis by dousing on 28 September 2021 by guest. Protected copyright. Statistical analysis oneself with a bucket of iced water or giving a donation—was moderately transmissible among a group of globally influential We used fully observed nomination chains to estimate the R0, celebrities. The celebrities took a mean 2.1 days (median 1 day) a measure of transmissibility, for a celebrities based cohort, up to accept the challenge (the serial interval). Our finding of an to the fifth generation seeded from each index case (the first R0 value greater than unity (1.43), indicating sustained spread, generation). R0 was estimated as the product of the mean number in a celebrities based cohort is consistent with observations of nominations (n) and the probability of successful nomination reported in the press. Indeed this social viral pandemic shares (p), assuming a branching process in which each participant of a similar R0 with pandemic A/H1N1 2009 influenza, or the high the Ice Bucket Challenge generates a random number of next end of the Middle East respiratory coronavirus since 2012 (table generation participants.