Respiratory infections, including the common cold and acute sinusitis, affect millions of individuals every year. Colds are caused by viruses, are easily spread from person to person, and are usually short-lived. Sinusitis (infection of the paranasal sinuses) usually occurs as a result of a cold but also can result from swelling of the nasal passages, obstruction from a medical device or a nasal deformity, or as part of a general infectious process in the body. Acute sinusitis is often caused by bacteria. Other, less common causes include fungus infection and parasites. Because sinusitis is often a bacterial infection (not just from a virus), antibiotic treatment may be used. It is important to understand that antibiotics do not help a cold. Using antibiotics improperly (such as for a viral infection) can cause resistant bacteria (that cannot be killed by the usual antibiotics) to form, leading to antibiotic-resistant infections. The December 5, 2007, issue of JAMA includes an article about acute sinusitis.