On 9 March, a patient who had recently traveled to Europe and had symptoms of COVID-19 visited the emergency department of St. Augustine’s, a private hospital in Durban, South Africa. Eight weeks later, 39 patients and 80 staff linked to the hospital had been infected, and 15 patients had died—fully half the death toll in KwaZulu-Natal province at that time. Now, scientists at the University of KwaZulu-Natal have published a detailed reconstruction of how the virus spread from ward to ward and between patients, doctors, and nurses, based on floor maps of the hospital, analyses of staff and patient movements, and viral genomes. Their 37-page analysis, posted on the university’s website on 22 May, is the most extensive study of any hospital outbreak of COVID-19 so far. It suggests all of the cases originated from a single introduction, and that patients rarely infected other patients. Instead, the virus was mostly carried around the hospital by staff and on the surfaces of medical equipment.