Why is it that a cold has to run its course, but antibiotics can cure a sinus infection?

Ginny

Colds are caused by viruses, but sinusitis may be caused by bacteria. Viruses respond only to antiviral medications, and there are precious few of these. We currently have drugs to treat HIV (human immunodeficiency virus, which causes AIDS) and the influenza and herpes viruses. The common cold is not caused by any of these viruses, so -- at least at present -- there is no "cure" for the common cold.
Viruses are small, simple microbes (compared with bacteria). A typical virus consists of a string of nucleic acids (DNA, for example) wrapped in a protein coat. They are little renegades that have the ability to commandeer a cell, "forcing" it to produce more viruses. The cell often dies in the process. At the very least, the commandeered cell is unable to perform its normal functions. When enough cells are affected, this results in illness.

Viruses are true parasites. They must parasitize living cells in order to reproduce themselves. They are not really "alive," so it is notoriously difficult to "kill" them once they are inside a living creature. (Most viruses can be destroyed by relatively simple maneuvers -- a little bleach, or some hot, soapy water -- IF they are outside the body.)

Bacteria, on the other hand, are, as microorganisms go, large and complicated. With few exceptions, bacteria do not require the living tissues of an animal in order to reproduce themselves. They must do all of the things that living things do to stay alive. They have to eat, reproduce and defend themselves from the environment and from predators. While they are only single-celled organisms, they are far more complex than even the largest viruses.

You may be wondering where I am going with this. Here's the bottom line: The more complex an organism is, the easier it is to kill. For example, imagine trying to "kill" (destroy the function of) a knife versus a food processor. With the knife, you don't have many choices. You can break it in half, you can melt it, or you can dull its edge so that it cannot cut. But a food processor is "dead" if you unplug it, snip any number of wires within the chassis, break the blade (or lose it), break (or lose) the plastic chamber that holds the food, break the buttons, fry the motor and so forth.

Since bacteria have many separate "components" that are necessary for bacterial life, there are many potential targets. Interfere with function A, B, C, D or E and the bacterium dies. Viruses, being simpler critters, offer fewer targets. And that's why bacterial infections are a whole lot easier to treat than viral infections.