Acupuncture is generally safe when done by an appropriately trained practitioner using clean technique and single-use needles. When properly delivered, it has a low rate of mostly minor adverse effects. Accidents and infections are associated with infractions of sterile technique or neglect of the practitioner. A 2013 review stated that the reports of infection transmission increased significantly in the prior decade. Serious adverse effects are rare, and as training standards and licensure requirements have been enhanced, the number of incidents has declined. A meta-analysis found that acupuncture for chronic low back pain was cost-effective as an adjunct to standard care, while a systematic review found insufficient evidence for the cost-effectiveness of acupuncture in the treatment of chronic low back pain.