The U.S. Food and Drug Administration issued four warning letters to companies selling over-the-counter products that claim to prevent methicillin-resistant Staphylococcus aureus bacteria, or MRSA, infections. The companies that received FDA warnings are Tec Laboratories, JD Nelson and Associates, Dr. G.H. Tichenor and Oh So Clean. Among the products the FDA says are mislabeled are several hand sanitizers and antiseptic gels. The FDA said the companies also claim to prevent infection from other disease-causing agents including E.coli bacteria and H1N1 flu viruses. The letters explain that the companies are violating federal law because there is no evidence to support that these products are effective for these purposes.