“An Outbreak of Common Colds at an Antarctic Base After 17 Weeks of Complete Isolation”, T. R. Allen, A. F. Bradburne, E. J. Stott, C. S. Goodwin, D. A. Tyrrell1973 (biology, microbiome)⁠:

6⁄12 men wintering at an isolated Antarctic base sequentially developed symptoms and signs of a common cold after 17 weeks of complete isolation.

Examination of specimens taken from the men in relation to the outbreak has not revealed a causative agent.

[They simply carried the cold with them in their microbiomes the whole time?]