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   Microbiology of Sinusitis (The microbiology of sinusitis is influenced by the   
   previous antimicrobial therapy, vaccinations, and the presence of normal flora   
   capable of interfering with the growth of pathogens)   
      
   Microbiology of Sinusitis    
    Authors    
   Itzhak Brook1    
   1Georgetown University School of Medicine, Washington DC    
   Correspondence and requests for reprints should be addressed to Itzhak    
   Brook, M.D., M.Sc., 4431 Albemarle Street, NW, Washington DC 20016. E-    
   mail: i...@georgetown.edu    
   Abstract    
      
   Most sinus infections are viral, and only a small proportion develops    
   a secondary bacterial infection. Rhinoviruses, influenza viruses, and    
   parainfluenza viruses are the most common causes of sinusitis. The    
   most common bacteria isolated from pediatric and adult patients with    
   community-acquired acute purulent sinusitis are Streptococcus    
   pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, and    
   Streptococcus pyogenes. Staphylococcus aureus and anaerobic bacteria    
   (Prevotella and Porphyromonas, Fusobacterium and Peptostreptococcus    
   spp.) are the main isolates in chronic sinusitis. Pseudomonas    
   aeruginosa and other aerobic and facultative gram-negative rods are    
   commonly isolated from patients with nosocomial sinusitis, the    
   immunocompromised host, those with HIV infection, and in cystic    
   fibrosis. Fungi and Pseudomonas aeruginosa are the most common    
   isolates in neutropenic patients. The microbiology of sinusitis is    
   influenced by the previous antimicrobial therapy, vaccinations, and    
   the presence of normal flora capable of interfering with the growth of    
   pathogens.    
   sinusitis bacteria Streptococcus pneumoniae Staphylococcus aureus    
   anaerobes    
   The upper respiratory tract, including the nasopharynx, serves as the    
   reservoir for pathogens capable of causing respiratory tract    
   infections, including sinusitis (1). Potential pathogens can relocate    
   during a viral respiratory infection from the nasopharynx into the    
   sinus cavity, causing sinusitis (2). Establishment of the microbiology    
   of all forms of sinusitis is of primary importance as it can serve as    
   a guide for choosing the adequate antimicrobial therapy. This review    
   presents the microbiology of all forms of sinusitis.    
   NASAL FLORA    
      
   The origin of organisms that are introduced into the sinuses and may    
   eventually cause sinusitis is the nasal cavity. The normal flora of    
   that site includes Staphylococcus aureus, Staphylococcus epidermidis,    
   α- and γ-streptococci, Propionibacterium acnes, and aerobic    
   diphtheroid (3–5). Potential sinus pathogens have been infrequently    
   isolated from healthy nasal cavities. These included Streptococcus    
   pneumoniae (0.5–15%), Haemophilus influenzae (0–6%), Moraxella    
   catarrhalis (0–4%), Streptococcus pyogenes (0–1%), and anaerobic    
   bacteria (Peptostreptococcus spp. [7–16%] and Prevotella spp. [6–8%])    
   (3–5).    
   The nasal cavity flora of patients with sinusitis is different from    
   healthy flora. Although the recovery of Staphylococcus spp. and    
   diphtheroids is reduced, the isolation of pathogens increases: S.    
   pneumoniae was found in 36% of patients, H. influenzae in more than    
   50%, S. pyogenes in 6%, and M. catarrhalis in 4% (6–10).    
   In many studies of the nasal bacterial flora in sinusitis a    
   simultaneous sinus aspirate was not taken (8, 9). Some studies found    
   the correlation between the floras to be poor (8, 11), whereas others    
   illustrated good correlation (9, 6, 11). In one study (6) in which the    
   sinus aspirate culture yielded a presumed sinus pathogen, the same    
   organism was found in the nasal cavity sample in 91% of the 185    
   patients. The predictive value of a pathogen-positive nasal finding    
   was high for S. pyogenes (94%), H. influenzae (78%), and S. pneumoniae    
   (69%), but was low for M. catarrhalis (20%).    
   Hsin and colleagues (12) demonstrated that when performed in pediatric    
   patients, the correlation between endoscopic middle meatal culture and    
   maxillary sinus puncture was only in 78%. The authors concluded that    
   endoscopic sampling is not as favorable in children as in the case of    
   adult patients.    
   Despite these encouraging data, nasopharyngeal culture is not an    
   acceptable alternative to culture through aspiration.    
   NORMAL SINUS FLORA    
      
   The question of whether normal bacterial flora in the sinuses exists    
   is controversial. The communication of the sinuses with the nasal    
   cavity through the ostia could enable organisms that reside in the    
   nasopharynx to spread into the sinus. After closure of the ostium,    
   these bacteria can become involved in the inflammation. Organisms have    
   been isolated from uninflamed sinuses in several studies (13–16). The    
   bacterial flora of noninflamed sinuses were studied for aerobic and    
   anaerobic bacteria in 12 adults who underwent corrective surgery for    
   septal deviation (13). Organisms were found in all aspirates with an    
   average of four isolates per sinus aspirate. The predominant anaerobic    
   isolates were Prevotella, Porphyromonas, Fusobacterium, and    
   Peptostreptococcus spp. The most common aerobic bacteria were S.    
   pyogenes, S. aureus, S. pneumoniae, and H. influenzae.    
   In another study, specimens were processed for aerobic bacteria only,    
   and Staphylococcus spp. and α-hemolytic streptococci were isolated    
   (14). Organisms were isolated in 20% of maxillary sinuses of patients    
   who underwent surgical repositioning of the maxilla (15). In contrast,    
   another report of aspirates of 12 volunteers with no sinus disease    
   showed no bacterial growth (16).    
   Jiang and colleagues (17) evaluated endoscopically the bacteriology of    
   normal maxillary sinuses. Organisms were recovered from 14 of 30 (47%)    
   swab specimens and 7 of 17 (41%) mucosal specimens.    
   Gordts and colleagues (18) reported the microbiology of the middle    
   meatus in healthy adults and children. Fifty-two (75%) adults had    
   bacterial isolates present, mostly S. epidermidis (35%),    
   Corynebacterium spp. (23%), and S. aureus (8%). In children, the most    
   common organisms were H. influenzae (40%), M. catarrhalis (34%), and    
   S. pneumoniae (50%).    
   INTERFERING FLORA    
      
   The nasopharynx of healthy individuals is generally colonized by    
   relatively nonpathogenic aerobic and anaerobic organisms (19, 20),    
   some of which are able to interfere with the growth of potential    
      
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