IT NOW seems almost certain that SARS is caused by a coronavirus. This family of viruses is known to cause serious disease in animals, and colds and intestinal infections in humans.
The steps necessary to prove that a particular pathogen causes a disease are called Koch’s postulates, after the 19th-century germ theory pioneer: you must find the agent in every victim, isolate it and grow it in culture, and then show the isolated agent causes the disease in lab animals.
Initially researchers in Germany and Canada reported seeing a paramyxovirus under the electron microscope in samples from SARS patients, while…
