chemical formula a combination of symbols used to express the chemical components of a substance. empirical formula a chemical formula that expresses the proportions of the elements present in a substance.
The bacteria streptococcus pneumoniae is the most common cause of acute bacterial sinusitis. This type of bacteria can be resistant to the most common types of antibiotics at standard dosages, although there are other antibiotics that can be used to treat the condition.
Bacteria are the most common direct cause of acute sinusitis. (Other organisms might be the infecting cause in less common cases.) The ability of bacteria or other organisms to infect the sinuses, however, must first be set up by conditions that create a favorable environment in the sinus cavities.