Attempts had been made in 1961 to recover smallpox virus by air sampling in smallpox wards and close to the mouths of smallpox patients, but these had been largely unsuccessful, possibly owing to the air sampling method used. Further attempts were therefore made in 1963, with a fluid impinger for air sampling and with Petri dishes placed below the orifice of the impinger to collect large droplets or particulate matter that the impinger might miss.Air samples from near the patients' mouths yielded little virus, this being more readily recovered from the settling-plates. Patients' bedclothes sampled with the impinger yielded rather more virus, but again even more was obtained from the Petri dishes.The results suggest that contamination of the air in the vicinity of smallpox patients is due to relatively large particles of infected dust from the patients' bedclothes rather than from fine droplets or droplet nuclei coming from the upper respiratory tract. Secretions from the mouth and upper respiratory tract appear to be responsible for the early contamination of pillows and bedclothes.
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