What is the main clinical marker for bacterial pharyngitis when testing a throat swab?

The primary clinical marker for bacterial pharyngitis, particularly when analyzing a throat swab, is the presence of Gram-positive cocci in chains. This finding is characteristic of Group A Streptococcus (GAS), the bacteria most commonly responsible for bacterial pharyngitis. When a throat swab is examined microscopically and shows this specific morphology, it strongly supports a diagnosis of streptococcal pharyngitis.

For further context, a negative rapid test would suggest that there is no significant finding of streptococcal infection, while viral cultures are typically not useful in the diagnosis of bacterial pharyngitis, as they target viral pathogens rather than bacterial ones. The presence of pus cells can indicate an inflammatory response, which may accompany either bacterial or viral infections, but does not specifically confirm a bacterial infection. Therefore, the identification of Gram-positive cocci in chains is the most definitive marker in this context.