Dear Dr. Theriot: Please clarify something for me. Ever since my daughter started pre-school, she has been getting colds. I usually take her to the doctor, and some of the times he gives her antibiotics, and other times not. Can you tell me when a cold needs an antibiotic?
First of all, a "cold" refers to an upper respiratory tract infection that is caused by a virus. There is usually sneezing, clear nasal discharge, nasal congestion and occasionally a low grade fever. Colds typically run their course within a week, after which, they resolve completely without any specific treatment.
In some cases, a lingering cold may become secondarily infected by a bacteria. This is usually the result of increased mucus production, congestion, and weakened body defenses (from the viral infection) which make the conditions just right for certain bacteria to take over and cause a secondary infection. When this occurs, the runny nose becomes thicker and is more yellow/green, the congestion becomes worse, there may be a deeper and more productive cough (bronchitis), the ears may have become infected, and there may be more of a fever. At this point, antibiotics are useful to fight the bacterial infection.
Viruses and bacteria are two very different groups of organisms. They differ greatly in size (bacteria are much larger), structure, and method by which they reproduce. Some antibiotics work by interfering with the bacteria's ability to reproduce. Other antibiotics work by attaching to, and destroying specific structures of the bacteria. Because of these differences, antibiotics are useless against viruses. There are scores of antibiotics available today, and only a few anti-viral drugs available.
The decision to use antibiotics (in a secondary infection) might seem arbitrary, but that is because each case is different and must be dealt with on an individual basis. There are no clear-cut rules--it boils down to a judgment call on the part of the doctor. This is a dynamic and changing process, and in most cases the "cold" clears up on it's own with time. Only a small number of these do go on the become secondarily infected.