In tort law, the stream of commerce theory refers to a principle that a person or entity that participates in placing a defective product in the general marketplace is strictly liable for harm caused by the product.

A Mississippi woman was give

n a vitamin shot in a doctor’s office and developed a severe infection with permanent scarring at the site of the injection. She claimed the injection had been contaminated and sued both the doctor and the manufacturer of the vitamin solution. The manufacturer said that nobody had tested the vial to show the vitamin solution was actually contaminated. However, the court said the injury was of the type

caused by a contaminated injection. The manufacturer was held liable under strict liability.

In a Texas case, a vial of medicine to be used in an eye operation was sterilized by placing it in a pan of strong formaldehyde solution. When the drug was drawn out of the vial and into a syringe, it was contaminated with the formaldehyde and caused serious eye damage. The patient sued the hospital and won. The court said that the hospital had made an implied warranty that the drug was fit for use in the eye. When it injured the patient, the hospital was liable. The woman could also have sued the manufacturer.

In a Nebraska case, a woman fell and fractured her hip. The doctors put in a prosthesis (artificial hip joint) that broke because of a manufacturing defect and had to be replaced. During the second operation, the patient died of a pulmonary embolism (blood clot to the lung). Since the second surgery would not have been necessary, if the prosthesis had not been defective, the family sued the manufacturer. They also sued the hospital as the retailer, because it had charged her insurance company for the prosthesis. Some surgeons buy their own surgical implants. If that had happened in this case, the doctor could have been held liable as the retailer. However, since he had not, and the patient’s death was not due to medical malpractice, the doctor was not sued.

There is an important exception to the stream of commerce theory. If a piece of equipment has been changed or modified in any way, after it was bought, that may cut off the liability of the manufacturer and everybody else “upstream”, who are only responsible for the device as it was sold. The people who altered it would be the only ones liable, especially if the alterations or repairs played any part in the injury. If the wheelchair’s brakes in the Wisconsin case we discussed earlier had failed because a hospital repairman had worked on them, the hospital would have been liable for the faulty repairs, and the manufacturer would have been cleared.