The microbiology of the middle meatus is similar in CRS patients and healthy individuals. Despite this, there was an important difference between the WBC count in these two groups, which helps to distinguish an infective from a saprophitic microorganism.

Thi s was a prospective study which assessed endoscopically collected middle meatus secretions in patients with chronic rhinosinusitis (CRS) and compared those findings with microbiological data of healthy individuals. Methods: Middle meatus samples were collected from 134 CRS patients. In the laboratory, samples were Gram stained for microscopic examination with white blood cels (WBCs) count and also send for aerobic, anaerobic and fungal cultures. Fifty volunteers served as control. Results: In CRS patients a total of 220 microorganisms were isolated. The most frequent microorganisms were Staphylococcus aureus (31%), coagulase-negative Staphylococcus (CNS) (23%). Gram-negative or facultative microorganisms were isolated in 37% of the samples, anaerobes in 12% and fungi in 14%. Seventy four percent of the samples with positive cultures presented many or few WBC. In the control group, 76% of cultures were positive for aerobes and 12% for fungi. No anaerobes were isolated. There were rare or no WBC in the fifty samples. The most frequent microorganisms were CNS (40%), Staphylococcus aureus (18%). Conclusion: The microbiology of the middle meatus is similar in CRS patients and healthy individuals. Despite this, there was an important difference between the WBC count in these two groups, which helps to distinguish an infective from a saprophitic microorganism.