Microbiology of Acute Sinusitis

Viral infection (mostly Rhino, influenza, adeno, and para-influenza viruses) is the most common predisposing factor for URTIs, including sinusitis. Viral infection can also concur with the bacterial infection. The mechanism whereby viruses predispose to sinusitis may involve viral-bacterial synergy, induction of local inflammation that blocks the sinus ostia, increase of bacterial attachment to the epithelial cells, and disruption of the local immune defense.

The bacteria recovered from pediatric and adult patients with community-acquired acute purulent sinusitis, using sinus aspiration by puncture or surgery, are the common respiratory pathogens (S. pneumoniae, H. influenzae, M. catarrhalis, and Group A beta-hemolytic streptococci) and Staphylococcus aureus (Table 1) (7-12). Following the introduction of vaccination of children with the 7-valent pneumococcal vaccine on 2000 in the U.S.A., the rate of S. pneumoniae

FIGURE 2 Viral and bacterial causes of sinusitis.

FIGURE 3 Dynamic of sinusitis: changes in bacteria recovered from the sinuses of two patients over time. Abbreviations: amox, amoxicillin; amox\clav, amoxicillin\clavulanic acid; cipro, ciprofloxacin; clinda, clindamycin. Source: From Ref. 3.

FIGURE 3 Dynamic of sinusitis: changes in bacteria recovered from the sinuses of two patients over time. Abbreviations: amox, amoxicillin; amox\clav, amoxicillin\clavulanic acid; cipro, ciprofloxacin; clinda, clindamycin. Source: From Ref. 3.

declined and H. influenzae increased (13). S. aureus is a common pathogen in sphenoid sinusitis (14), while the other organisms are common in other sinuses.

The infection is polymicrobial in about a third of the cases. Enteric bacteria are recovered less commonly, and anaerobes were recovered only from a few cases with acute sinusitis. However, appropriate methods for their recovery were rarely employed in most studies of acute sinusitis.

Anaerobic bacteria account for about 8% of isolates and are commonly recovered from acute sinusitis associated with odontogenic origin, mostly as an extension of the infection from the roots of the premolar or molar teeth (15,16).

Pseudomonas aeruginosa and other aerobic gram-negative rods are common in sinusitis of nosocomial origin (especially in patients who have nasal tubes or catheters), the immunocom-promised, patients with human immunodeficiency virus (HIV) infection and cystic fibrosis (17). However, anaerobic bacteria can also be recovered in these patients.

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