The influence of building characteristics including ventilation on the spread of viral respiratory infections has begun to receive increased attention from the public, government, media and scientists [10] . Brundage et al. [11] studied the risk of febrile acute respiratory diseases at four army training centers and found that disease rates were significantly higher among trainees in modern energy efficient barracks that had a low ventilation rate. Menzies et al. [12] suggested that there was a relationship between lower ventilation rates and more frequent tuberculosis infections among hospital workers. Milton et al. [13] reported an association between sick leave of employees and outdoor air supply rate. Myatt's [14] study showed that the probability of detecting airborne rhinoviruses was positively associated with weekly average CO 2 concentration in an office. Other factors found to be associated with rate of infectious diseases include occupancy level [15] , cleaning routines and ''damp'' buildings [16] . With respect to crowding, direct and surface contact as well as airborne transmission both appears to be factors in disease transmission. Hoge et al. found that severe overcrowding and inadequate ventilation contributed to an outbreak of pneumococcal disease in a large urban jail [17] .