Assessing Mycoplasma hyopneumoniae aerosol movement at several distances

followed by a manual injection of 200 ml of air (Dee and others 2005). Throughout the study, this mixture was considered to be one aliquot of aerated M hyopneumoniae. For the dissemination of each aliquot over the three distances, a Dayton split capacity blower was used to pull aerated M hyopneumoniae down a straight plastic tube 10 cm in diameter. Finally, a portable air centrifuge (Spin Con 450; Camber) was used to collect M hyopneumoniae-inoculated air samples exhausted from the blower following transport through the tube (Fig 1). This instrument was capable of collecting 450 litres of air per minute. During the process of air collection, sterile saline was automatically injected into the air centrifuge, rinsing the interior of the centrifuge drum and pooling any particles in a 10 ml aliquot for diagnostic evaluation. The study consisted of a total of six replicates, two replicates being conducted at each distance. During each replicate, one aliquot of aerated M hyopneumoniae was dispersed and a 60 minute air-collection period was employed. Each replicate also included a positive control, a protocol control and a sanitation control. The positive control consisted of collecting aerated M hyopneumoniae dispersed directly from the utensil without the use of the tube model, while the protocol control consisted of testing M hyopneumoniae-free Friis medium to ensure that the aforementioned procedure itself did not result in cross-contamination. Both controls were conducted between each replicate that utilised M hyopneumoniae-positive aerosols. Between each replicate, the model and the air centrifuge were sanitised. To thoroughly sanitise the pipe, it was disassembled into separate 10 m sections and swabbed using a rag immersed in 10 per cent bleach solution and another immersed in sterile water, which were attached to a 10 m extension pole and applied to the inner surface of each section of pipe. The air centrifuge was disinfected by an automated process that involved rinsing the interior of the instrument with 10 per cent bleach solution according to the manufacturer’s instructions. Following completion of the sanitation of the centrifuge, its inner workings were rinsed with sterile saline and a 10 ml sample was collected for diagnostic testing to ensure the absence of M hyopneumoniae (the sanitation control). During all replicates, the temperature, relative humidity and velocity of the air transported through the tube were measured using a Kestrel weather meter (Nielsen-Kellerman). The instrument’s impeller was inserted 5 cm into the lumen of the pipe and readings were taken at 1, 75 and 150 m. All air samples and the sanitation controls were tested for the presence of M hyopneumoniae DNA by the nPCR assay as previously described by Calsamiglia and others (1999). The results of air flow parameters are summarised in Table 1. Air velocity readings of 11·75 m/s (42 km/hour) were recorded over the 150 m distance, while the mean temperature and relative humidity recorded over this distance were 9·2°C and 49 per cent, respectively. All air