We have estimated the numbers of aerosols exiting the vuvuzela when blown by male and female adults. In triplicate experiments from eight individuals the mean concentration of particles exiting the vuvuzela was 658,000 per litre. The mean peak volume of air exiting the instrument was 6.1 litres per second. Thus we estimate that approximately 4 million particles per second were being disseminated from the vuvuzela at peak blowing times. For shouting we estimated a peak aerosol concentration of 3,700 per litre or 7,000 particles per second (assuming peak flow volume of 1.8 Ls−1
). The data we obtained for shouting is in broad agreement with a recent study of particles exhaled by healthy adults during normal to deep breathing (tidal volume range: 20–80%) where between 5 and 5,000 droplets per litre were recorded 
. The differences we observed between male and female volunteers might be explained by differences in their lung capacities, however this was not measured 
. Our results suggest that the vuvuzela is an efficient means of propagating large numbers of aerosols. The great majority of particles measured were of a size that could remain suspended in the air as droplet nuclei and would be capable of entering the alveolar airspaces of the lung. During normal (resting) breathing an adult inhales approximately 7 litres of air each minute, of which 5 litres reaches the respiratory bronchioles 
. When attending a sporting event and surrounded by vuvuzela players a spectator could expect to inhale large numbers of respiratory aerosols over the course of the event. Actual exposure would be affected by the proximity of the vuvuzelas and ambient ventilation which would serve to dilute the stream of particles.
The large number of aerosols emitted by the vuvuzela raises the possibility that, if used by persons with an infection of the respiratory tract, they could act a conduit for the spread of infectious particles. For ethical and safety reasons we only examined healthy volunteers during this study; assessment of pathogenicity of aerosols disseminated by the vuvuzela will require further study using patients with known respiratory infections. Aerosols can be created at various locations within the respiratory tract 
and carriage of pathogens by exhaled aerosols depends on the site of infection and the quantity pathogenic particles in the airways 
We speculate that aerosols propagated while blowing the vuvuzela may originate in either the lower or upper respiratory tract, or the mouth. To obtain the desired trumpet sound when blowing the vuvuzela air is forced through the lips into the opening of the instrument which may serve to create further aerosols, or alter the size of droplets produced elsewhere in the respiratory tract. In addition to the manner in which the instrument was blown the number of contaminated particles expelled will vary according to the pathogen, the site of infection and the extent of disease. Some infections may result in inflammation and physiological changes within the respiratory tract that would affect the person's capacity to blow the vuvuzela 
. In addition, some conditions are associated with changes in the rheology of respiratory secretions that might affect aerosol formation 
. Studies of cough aerosols from pulmonary tuberculosis patients and cystic fibrosis patients with bacterial infections found that the concentration of infectious particles varied widely between patients 
. To attain an accurate assessment of the vuvuzela's potential to disseminate infected aerosols, sample sizes will need to be increased to include individuals having a range of upper and lower respiratory tract infections. Symptomatic and non symptomatic carriers should be assessed. In addition to counting the number and size of particles, the viability of infectious particles should also be assessed. For bacterial infections this might be achieved by modification of a cough aerosol sampling system previously used to assess tuberculosis patients 
Coughing, sneezing, singing and talking can all produce aerosols capable of transmitting airborne respiratory diseases 
. Reports from earlier investigators suggest that coughs may produce up to 5,000 droplet nuclei and a sneeze may generate as many as 900,000 particles 
. The data we present suggests that blowing the vuvuzela for even a short time period has the potential to create more droplet particles than either coughing or sneezing.
There were some limitations to this study that may have had an impact on the results. The particle counter used to assess the concentration of particles recorded measurements at one second intervals and it is possible that the peak values recorded were not the maximum level of particle produced. As it was not possible to assess variation in flow rates over the blowing period the total number of particles expelled during a blowing or shouting event could not be estimated. The performance of individuals and production of aerosols may have been influenced by their respective lung capacities 
, this factor was not assessed in the experiment. The use of a paper cone to assess the droplets from shouting was not ideal as the surface areas and shape of the paper cone may increase the chance that particles attach to the surface rather than remain in the airstream, affecting the number and size of particles reaching the counter. As exhaled air cools and mixes with ambient air condensation droplets may form. Although ambient air temperature and humidity remained similar in all experiments, the difference in shape between the cone and the vuvuzela may have affected the mixing and rate of formation of these transient droplets. A further consideration is that only healthy individuals were recruited for this study, and as described above, it is possible that people with respiratory illness with impaired lung function would perform differently when blowing the vuvuzela. Nonetheless we have demonstrated that these plastic trumpets provide an excellent means of propagating respiratory aerosols, exceeding both sneezing and coughing as a means of disseminating droplet nuclei and we conclude that their potential to spread respiratory diseases requires further investigation. The frequency, duration, and vigor of vuvuzela playing will vary considerably from person to person, depending on the occasion and their expertise at blowing and we are unable to comment on the number of aerosols produced during an entire sporting event. A further factor is the environment in which they are used; open situations with a strong draft or breeze will serve to rapidly dilute the aerosols produced but transmission risks may be considerably higher in enclosed arenas. A further risk factor for disease transmission will be the density of vuvuzela players and the prevalence of respiratory infections in the population.
As far as we are aware this is the first report in the scientific press regarding the issue of aerosol dissemination by the vuvuzela and no epidemiological data regarding impact of the instrument on disease transmission have been reported. Similarly there have been no reports of disease transmission from sharing vuvuzelas, or from transfer of non aerosolized respiratory secretions that collect inside the instruments. The vuvuzela has become popular in South Africa, a country with the highest urban prevalence of tuberculosis in the world and that recently experienced a measles epidemic 
. It has been used at domestic soccer games for the past decade and was adopted by many visiting fans during the 2010 FIFA World Cup competition. The tournament was held during late June and early July and coincided with the annual flu season. Surveillance reports show an increase in the proportion of influenza B compared to previous years, but evidence to link this to the presence of visiting spectators is not presented 
. Similarly a number of measles cases were confirmed amongst visitors from other countries but evidence as to the source of their infections is not available 
. The plastic vuvuzela is believed to have emerged as a child's toy, before being adopted by sports fans in Africa and parts of Asia, where it is a multi-million dollar industry. In Africa it has become a symbol of the soccer industry but vuvuzelas are also blown by fans of cricket and rugby football. They have been banned from a number of sports grounds due to the volume of noise emitted and safety concerns arising from their ability to nullify public address systems. Studies have previously suggested that vuvuzela playing poses a risk of noise induced hearing loss 
. We recommend that consideration is taken of their propensity to disseminate respiratory aerosols and that persons with respiratory infections be advised not to blow their vuvuzela in places where they risk infecting others. This should include enclosed spaces and crowded venues such as large sporting events. We also recommend that research be commissioned to determine the risks to public health posed by the vuvuzela.