SHORT-DURATION EXPOSURE AND THE TRANSMISSION OF RHINOVIRAL COLDS

Transmission of infection with rhinovirus type 55 was attempted under natural circumstances of interaction among 26 experimentally infected donors and 33 antibody-free (titer, < 1:3) recipients. In a total of 3 experiments, only 2 recipients (6%) became infected. In the 1st experiment no transmissions from 5 donors to 9 recipients occurred after 2-3 h of loud vocalization and card playing in a small room. In the 2nd experiment a cold was transmitted to 1 (9%) of 11 recipients living in dormitory rooms for 36 h in groups consisting chiefly of 2 donors and 2 recipients. In the 3rd experiment, 1 (8%) of 13 recipients was infected after kissing an infected donor. In studies with rhinovirus type 16, the median human infectious dose was found to be 0.28 TCID50 (median tissue culture infectious dose) in the nose, 2260 TCID50 on the tongue and 11,000 TCID50 on the external nares. Rhinoviral infections are difficult to transmit by short-term natural exposure, perhaps because the agent must be present in overwhelming numbers to reach susceptible mucosal cells.