There is a close genetic relationship between SARS coronavirus (SARS-CoV) and the causative agent of COVID-19, SARS-CoV-2. The predominant expression of ACE2 in the lower respiratory tract is believed to have determined the natural history of SARS as an infection of the lower respiratory tract 5. Although the positive detection of SARS-CoV-2 in clinical specimens from the upper respiratory tract has previously been described 9, 10, these observations do not address the principal differences between SARS and COVID-19 in terms of clinical pathology. The patients who were studied here were enrolled because they acquired their infections upon known close contact to an index case, thereby avoiding representational biases owing to symptom-based case definitions. All patients were treated in a single hospital in Munich, Germany. Virological testing was done by two closely collaborating laboratories that used the same standards of technology for PCR with reverse transcription (RT-PCR) and virus isolation; these two laboratories confirmed each other's results in almost all of the individual samples. Owing to the extremely high congruence of results, all data--except for the serological data (which are based on results from one laboratory only)--are presented together. The patients are part of a larger cluster of epidemiologically linked cases that occurred after 23 January 2020 in Munich, as discovered on 27 January (ref. 11). The present study uses samples taken during the clinical course in the hospital, as well as from initial diagnostic testing before admission. In cases in which this initial diagnostic testing was done by other laboratories, the original samples were retrieved and retested under the rigorous quality standards of the present study.