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Microbiology of Acute Otitis Media

D. Vicheva, I. Jovchev

Department of Otorhinolaryngology, Medical University, Plovdiv, Bulgaria

ABSTRACT

Objective: Acute otitis media is one of the most common causes of pain children and newborn infants. The aim of this study is to review the current concepts for diagnosis and treatment of this disease.
Setting: Department of Otorhinolaryngology, Medical University, Plovdiv, Bulgaria
Data sources: Literature data collected from 22 different sources, personal observations and findings.
Conclusion: The frequency of acute otitis media caused by Streptococcus pneumoniae and Haemophilus influenzae as the most important pathogens is stable over the time. Streptococcus pneumoniae shows exellents susceptibility to (amino) penicillins. The great majority of strains indicated in acute otitis media maintain aminopenicillin susceptibility. Branhamella catarrhalis must now be considered as the third most important pathogen. There are no essential differences between the microorganisms cultured in primary acute otitis media compared to those isolated recurrent acute otitis media. Amoxicillin-clavulanate (Augmentin, Amoksiklav, Curam) shows good antimicrobial activity agains all major pathogens responsible strains of Haemophilus influenzae and Branhamella catarrhalis. This drug also shows good penetration of middle ear fluids in therapeutic concentration.
Key words: Microbiology, Acute Otitis Media, Review of Literature.
Pro Otology 2-3:104—106, 2004

INTRODUCTION

The aim of this study is to review current knowledge on the microbiology of acute otitis media, with special reference to its relevancy for clinical management. In studying acute otitis media a proper understanding of its microbiological aspects is essential.

ROLE OF BACTERIA: Bacteria play an important role in the pathogenesis of acute otitis media. A complication of 13 studies, in which 4157 cases of acute otitis media were bacteriologic ally evaluated, showed positive cultures in approximately 70% of the cases (1-3). Similar finding were reported from 12 different studies conducted in United States, Finland and Sweden (2,4). More recent reports showed even higher percentages of positive cultures in acute otitis media, ranging from 84% to 93% (5,6).

ROLE OF VIRUS: A direct role of viruses in the etiology of acute otitis media does not seem to be present at the level of the middle ear (7). Directly isolated from middle ear effusions, viruses were reported in only 4.4% and 4.5% of acute otitis media (8). However, as clinical experience shows, acute upper respiratory tract infection or is preceded by it. Viral involvement of the upper respiratory tract mucosa, including eustachian tube and middle ear cavity, may facilitate the concurrent development of the middle ear infection.

Henderson and co-workers showed a clear correlation between isolation of viruses in the upper respiratory tract and the presence of otitis media. In this longitudinal study a concurrent or recent viral infection was found in 26.3% of the cases (9).

Isolation of viral antigens is another way to detect a possible role of viruses in patients suffering from acute otitis media. This yields virus antigens from ±25% of the cases (10). Various studies showed that particularly respiratory syncytial virus (RSV) is associated with acute otitis media (11).

STERILE CULTURES: Negative culture results, reported in around 30% of the cultures, do not necessary imply that pathogenic microorganisms are not associated with the infection process. The bacterial organism, such as an anaerobic bacterium, may not have been isolated by usual laboratory techniques (12). Also, the presence of antimicrobial enzymes such as lypozymes, alone or in combination with immunoglobulins, or recent administration of antibiotics may already have suppressed bacterial growth (12). Non-bacterial organisms as viruses, Chlamydia, or Mycoplasma may be involved (12).

In this respect the use of the Gram stain is of value in identifying fastidious bacterial organisms. This technique may demonstrate their presence in cases where antibiotics or antimicrobial substances may have inactivated bacterial growth (12).

Another way to determine bacterial involvement in acute otitis media is by detecting antibodies to specific microorganisms during the course of an episode of acute otitis media. Using this technique Karjalainen et al. clearly demonstrated that in culture – negative acute otitis media, bacteria specific secretory antibodies were found in 21% of the ears with “culture-negative” acute otitis media at the initial visit, compared to 36% of the ears with “culture-positive” acute otitis media. Also, they found that the appearance of secretory antibodies did not correlate with the number of preceding acute otitis media attacks, a percentage increasing during the course of the infection (11).

PREDOMINANT BACTERIAL PATHOGENS: Streptococcus pneumoniae is consistently reported to be the most frequently occurring pathogen, followed by Haemophilus influenzae. In earlier years the third most frequent microorganism was Streptococcus Group A (3). However, studies conducted in the eighties showed an increasing number of Branhamella catarrhalis (4). Culture results from the Pittsburg Otitis Media Research Center between 1980 and 1989 clearly showed Branhamella catarrhalis to be the third most frequent pathogen in acute otitis media (5). In one recent report this microorganism emerge as the second most frequent pathogen in acute otitis media, found in 26% of the cultures (6).

In a later study the most predominant microorganism was Streptococcus Group A (14). Thus far this isolated finding cannot be confirmed by other studies. This anomalous finding cannot be explained. Even when the fact is taken into account that the study population consisted of children whose acute otitis media episode took an unsatisfactory course; all patients suffered from persistent earache and/or fever three days from onset of an untreated acute otitis media episode. Recently, a study from Denmark reported the reappearance of Streptococcus Group A in acute otitis media, with an increasing percentage of this microorganism in cultures (15). The decrease in Streptococcus pneumoniae was not statistically significant, with unchanged percentages of Haemophilus influenzae and Branhamella ctarrhalis. Latter finding suggest a transient epidemic of Streptococci Group A, rather than a consistent rise and reappeance of Streptococcus Group A, rather than a consistent rise and reapperance of streptococcus Group A as an important microorganism in acute otitis media (15).

Although in children younger than tree months a more predominant role is found for gram-negative enteric bacteria, such as Escherichia Coli, Klebsiela and Enterobacter species, even in this group the most common pathogens an acute otitis media are Streptococcus oneumoniae and Haemophilus influenzae (16).

ORIGIN BACTERIAL PATHOGENS IN ACUTE OTITIS MEDIA: By now, it is well understood that the source of the most common middle ear pathogens is in the nasopharynx and that they belong to the normal flora of both healthy and otitis-prone persons (15). A study on antibiotics sensitivities of nasopharyngeal pathogens in a relapse of acute otitis media again demonstrated the nasopharynx as the source of microbial invasion of the middle ear (16). The lower frequency of acute otitis media in older children may be explained by the finding that middle ear pathogens in the nasopharynx diminish in number with advancing age (15). Because of their clear predominance only the three most important pathogenic microorganisms are discussed separately below.

STREPTOCOCCUS PNEUMONIAE: This microorganism is consistently reported to be the sole pathogen in 30% to 40% of the cultures. This proportion does not seem to vary much with age (9). Pneumococci, isolated from otitis media, are invariably encapsulated with plysaccharides, pneumococci without capsular polysaccharides may be considered non-pathogenic (17). Currently, 85 capsular polysaccharide types are recognized. Of these, relatively few types are associated with acute otitis media; 10 to 15 types 1, 3, 6A, 7F, 14, 18C, 19F, 23F. Less commonly associated are types 2, 4, 5, 8, 9N, 12F, 25F (19). The capsular type does not have direct implications for possible antibiotics therapy, but it determines the pneumococcal vaccine composition. Because immunoprophylactic therapy is beyond the score of this review, it will not be discussed further.

HAEMOPHILUS INFLUENZAE: This microorganism is consistently reported to be the sole pathogen in about 20% of the cultures. Non-typable or unencapsulated types account for 85% to 90% of the cases of acute otitis media caused by Haemophilus influenzae, where by Haemophilus influenzae type B is responsible for the remaining 10% to 15% (18). Typable Heamophilus influenzae strains are found in six different capsular types, a through F (18). The earlier notion that Haemophilus influenzae otitis media is predominantly a disease of children in the preschool age is not entirely accurate. The microorganism is comparably frequent in acute otitis media at older age. The first reports of β-lactamase produsing strains of Haemophilus influenzae, causing resistance to aminopenicillins. The some investigators reported, that the microorganisms was cultured somewhat more frequently (17% in recurrent or prolonged episodes of acute otitis media than in primary attacks (8%) (21). In a large European multicenter study Haemophilus influenzae strains from different specimen sources were compared in standardized way with respect to β-lactamase – production, capsular types and resistance to different antibiotics (20). This revealed an overall mean percentage of 11% β-lactamase – producing strains, more often (17%) in type B, than in non-B strains (10%).

BRANHAMELLA CATARRHALIS: This microorganism has emerged during the past two decades as an increasingly important pathogen in acute otitis media. In some studies it is detected in up to 26% of the children suffering from acute otitis media (10). A predilection for the younger children has been reported (12), though others could not confirm this finding within the first four years of life (20). A majority of the strains are β-lactamase – producing.

INDIRECT PATHOGENICITY OF β-LACTAMASE PRODUCING MICROORGANISMS: apart from playing a direct role in the infectious process, β-lactamase – producing strains of Haemophilus influenzae or Branhamella catarrhalis may also act as indirect pathogens by protecting penicillin – susceptible organisms from this drug. This concept of indirect pathogenicity by β-lactamase – producing microorganisms has been illustrated by Brook (22).

CONCLUSIONS

In our review of current knowledge on the microbiology of acute otitis media, the following conclusions can be drawn.

Firstly, considerable stability over time exists in the frequency of acute otitis media caused by Streptococcus pneumoniae and Haemophilus influenzae as the most important pathogens. Up to now, Streptococcus pneumoniae shows exellents susceptibility to (amino) penicillins. Although β-lactamase – production is reported for Haemophilus influenzae, the great majority of strains indicated in acute otitis media maintain aminopenicillin susceptibility.

Secondly, Branhamella catarrhalis must now be considered as the third most important pathogen. The majority of strains from this microorganism are reported to be β-lactamase – producing.

Thirdly, so far the literature gives no evidence of essential differences between the microorganisms cultured in primary acute otitis media compared to those isolated recurrent acute otitis media.

Fourthly, in view of current knowledge of the most likely pathogens involved in acute otitis media, cultures from middle ear aspirates are not necessary in overwise healty children of six months and older. Amoxicillin-clavulanate (Augmentin, Amoksiklav, Curam) shows good antimicrobial activity agains all major pathogens responsible strains of Haemophilus influenzae and Branhamella catarrhalis. This drug also shows good penetration of middle ear fluids in therapeutic concentration (13,14,22).

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