Viral and bacterial interaction in acute otitis media (2000)

Researchers have long known that viruses and bacteria can mutually interact in the pathogenesis of disease; however, the specific interactions in cases of acute otitis media (AOM) have not been fully examined. Evidence gathered in the past two decades suggests that viruses play a significant role not only in the pathogenesis but also in the recovery from the disease. Viral infection of the upper respiratory tract induces Eustachian tube dysfunction and microbial invasion of the middle ear. These conditions lead to acute inflammatory changes and signs and symptoms of middle ear infection. 1 By the time AOM is diagnosed viral infection of the upper respiratory tract may have been aborted, and the virus may never enter the middle ear. If the virus enters the middle ear along with bacteria or if the viral upper respiratory tract infection (URI) is still ongoing at the time of AOM diagnosis, evidence suggests that the virus may interact with the bacteria, leading to adverse outcomes of AOM. The role of viruses in the pathogenesis of AOM is reviewed in the preceding article. This review presents (1) clinical evidence of viral and bacterial interaction that occurs by the time AOM has been developed, (2) effects of the interaction on the clinical course of AOM and recovery and (3) potential mechanisms of the interaction. VIRUS TYPES IN AOM AND THEIR RELATIONSHIP WITH BACTERIA Although 3 types of bacteria, Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis, cause almost all AOM involving an intact tympanic membrane, many types of viruses are associated with URI that can lead to AOM. 2 Evidence indicates that from time to time these viruses do enter the middle ear. Overall viruses have been detected in 8 to 25% of the middle ear fluid (MEF) from children with AOM. 3–11Table 1 summarizes data from 708 patients with AOM whose MEFs were studied for viruses and bacteria. 6, 9, 12, 13 These data show that bacteria alone were in the MEF of 55% of these patients, viruses and bacteria together were detected in 15% and viruses alone were detected in another 5% of cases. The types of viruses detected in the MEF include respiratory syncytial virus (RSV), parainfluenza viruses (types 1, 2 and 3), influenza (A and B), rhinovirus, adenovirus, enterovirus, herpes simplex virus, cytomegalovirus and coronavirus. 3–11, 14Table 2 illustrates various types of viruses detected in the MEF from 708 children with AOM shown in Table 1. 6, 9, 12, 13Table 1: Presence of bacteria and viruses in the middle ear fluid of children with acute otitis media*Table 2: Types of viruses detected in the middle ear fluid from 708 patients with acute otitis media*Similar to the varying importance of different types of bacteria in the cause of AOM, the importance of each virus type may vary. At present data on types of the viruses show RSV to be one of the most common viruses associated with AOM. Of all the viruses listed previously the frequency of AOM in children with URI associated with RSV was the highest (33 to 57%). 15, 16 RSV also had the highest middle ear invasion rate (74%), as determined by detection of specific virus or virus antigen in the MEF vs. detection of the same pathogen in all patients’ clinical samples. 12 The rate of middle ear invasion by other viruses was lower: 52% for parainfluenza viruses; 42% for influenza; 11% for enterovirus; and 4% for adenovirus. The data on the role of rhinovirus in AOM are controversial, probably because of the different methods of diagnosis used in the published studies. An earlier study in which tissue culture was used for viral diagnosis has shown that children infected with rhinovirus have the lowest frequency of AOM (10%) compared with those infected with other respiratory viruses (16 to 33%). 15 A recent study of children with AOM, using multiplex reverse transcription polymerase chain reaction (RT-PCR) assay for viral diagnosis, has found rhinovirus to be a more common cause of OM than RSV and coronavirus. 14 This latter study also found that the rate of middle ear invasion by rhinovirus was the highest (69%) compared with RSV (65%) and coronavirus (44%). These new data about the prevalence of rhinovirus in AOM are most important because when rhinovirus interacts with bacteria it may cause more severe AOM than other viruses. Sung and colleagues, in a study of 71 children who had combined bacterial and viral infection of the middle ear compared 2 groups of patients according to bacteriologic response to treatment. 17 The group with bacteriologic failure 2 to 4 days into appropriate antibiotic treatment were similar to the group with bacteriologic cure in all respects (i.e. patients’ age, gender, race, history of recurrent AOM, duration of respiratory symptoms, type of antibiotic used and type of bacteria in the MEF). The only difference noted was the type of viruses found in the MEF. The presence of rhinovirus was associated with a higher rate of bacteriologic failure than other virus types. Further studies are required to confirm the relative virulence of rhinovirus and to explore the mechanisms of rhinovirus-bacterial interaction in AOM. Although influenza viruses (types A and B) are less commonly found associated with AOM, they are of interest for 2 reasons. First, because influenza virus vaccines are the only respiratory virus vaccines available at present, they offer the only strong evidence for the effect of viral vaccines on AOM. Studies have shown that prevention of influenza by vaccines can also prevent AOM associated with this virus during influenza season. 18, 19 Second, influenza viruses offer evidence of relationships between types of viruses and bacteria. Influenza A seems to be synergistic with S. pneumoniae in producing otitis media (OM) in experimental animals. 20 A recent study of children with AOM has also shown close relationship between S. pneumoniae and influenza virus. 12 In the MEFs that contained both bacteria and virus, S. pneumoniae was cultured significantly more often in the MEF containing influenza virus than in those containing RSV or parainfluenza virus. EFFECTS OF VIRAL AND BACTERIAL INTERACTION ON CLINICAL COURSE AND RECOVERY OF AOM Studies support the hypothesis that viruses interact with bacteria and that concurrent viral infection of either the middle ear or the respiratory tract outside the middle ear can significantly worsen the clinical course of bacterial AOM. In the chinchilla model of experimental OM, studies have shown that bacteria (S. pneumoniae or H. influenzae) and/or virus (influenza A or adenovirus) can induce OM. 20, 21 The incidence of OM was higher in animals with combined bacterial and viral infection than those with either bacterial or viral infection alone. In this model the severity of OM (as measured by the degree of tympanic membrane inflammation, middle ear pressure and ciliary activity) was also greater in animals receiving both bacteria and virus (combined infection) than in those receiving bacteria or virus alone. 21 Despite the availability of numerous effective antibiotics, children with AOM often experience poor clinical response. Physicians generally change the type of antibiotic when this happens, assuming that bacteria resistant to the initial antibiotic cause the treatment failure. However, resistant bacteria have been responsible for only a small percentage (19 to 22%) of cases of treatment failure. 22, 23 Investigations indicate that concurrent viral infection of the middle ear and/or respiratory tract cause antibiotic treatment failure in children with AOM. In a small study of 58 children with AOM during a respiratory viral season, bacteriologic failure at 2 to 4 days into antibiotic therapy occurred in a significantly higher proportion of patients who had both bacteria and viruses cultured from the MEF (50%) than in the group with bacteria alone (13%, P < 0.01). 9 The patients with persistently positive viral cultures of the MEF also had purulent OM of longer duration. In a subsequently larger prospective study of 271 children with AOM, which included comprehensive virologic studies, including viral antigen detection, culture and serologic screening, similar results were obtained (Table 3). 10 More patients with combined bacterial and viral infection had persistent OM than did patients with only bacterial infection or only viral infection. In a third study of 88 patients Arola et al. 8 reported that respiratory viral infection caused prolonged symptoms of AOM. Viruses were isolated from the MEF and/or nasopharynx significantly more often in the patients unresponsive to antibiotic treatment (68%) than in those initially diagnosed with AOM (41%;P < 0.05). A follow-up of patients who were initially diagnosed with AOM also showed that prolonged symptoms occurred in a higher proportion of children for whom viruses were present in the MEF (44%) than of those with no virus in the MEF (11%, P < 0.05). Table 3: Clinical course of acute otitis media according to the types of associated pathogens*MECHANISMS OF VIRAL AND BACTERIAL INTERACTION The mechanisms by which viruses interact with bacteria and result in enhanced severity of AOM or in adverse clinical and bacteriologic outcomes of the disease are still unclear. Concurrent viral infection of the respiratory tract and/or the middle ear may enhance the degree of inflammation, leading to increased mucosal damage; or it may affect immunologic and physiologic responses, leading to delayed bacterial elimination from the middle ear. Some hypothetical mechanisms that have been explored include: (1) virus causing delayed clearance of bacteria from the middle ear; (2) virus interfering with penetration of antibiotic or diluting antibiotic concentrations in MEF; and (3) virus inducing local production of cytokines and inflammatory mediators, leading to enhanced severity and more prolonged infection. Virus-induced delayed clearance of bacteria from the middle ear. In the chinchilla model of OM the animals that were inoculated intranasally with influenza A virus or S. pneumoniae with influenza A demonstrated neutrophil dysfunction, as expressed by decreased chemiluminescent, chemotactic and bactericidal activities. 24 Direct inoculation of influenza A virus into the middle ear of the animals resulted in capillary engorgement, subepithelial hemorrhage, tissue edema and acute inflammatory cell infiltration, as well as decreased ciliated activity of the Eustachian tube epithelium and Eustachian tube transport function. 25, 26 These findings suggest some mechanisms of virus-induced delayed bacterial clearance from the middle ear. Middle ear pharmacokinetics of antibiotics The data to support the hypothesis that viral infection induces local inflammation and immunologic reactions that interfere with penetration of antibiotic or dilute antibiotic concentration in the MEF first came from an experimental animal model studying middle ear antibiotic penetration. Jossart et al. 27 compared middle ear drug penetration rates for amoxicillin, sulfamethoxazole and trimethoprim. They found decreased penetration of antimicrobials occurring with virus infection (influenza A) and combined virus and bacterial infection (influenza A and S. pneumoniae) compared with infection with bacteria alone. More recently amoxicillin MEF penetration and pharmacokinetics were studied in 30 children with AOM. 13 The data from this small study were consistent with those shown in the chinchilla model. After a 25-mg/kg oral dose amoxicillin reached its peak in the MEF in ∼3 h. Geometric mean amoxicillin concentrations in the MEF were lowest in virus-infected children (2.7 μg/ml), higher in children with combined bacterial and viral infection (4.1 μg/ml) and highest in children with bacterial-only infection (5.7 μg/ml). Further clinical studies with larger numbers of subjects are required to confirm these findings. Cytokines and inflammatory mediators in bacterial, viral and combined infections As in the case of any acute infection within a normally sterile space, clinical signs and symptoms of the middle ear infection are most likely derived from activation of the inflammatory defense system against invasion of microbes. 28 Bacteria and viruses are capable of inducing complex interaction of proinflammatory cytokines and inflammatory mediators at the infected sites (i.e. meninges, respiratory tract). 29–36In vitro data have also shown that respiratory viruses are capable of inducing production of leukocyte histamine-releasing factor, as well as enhancing IgE-mediated histamine release. 37, 38 Although data on the molecular pathogenesis of AOM are sparse, the findings of numerous cytokines and inflammatory mediators in the MEF from patients suggest that the operating mechanisms in OM are similar to those observed in other infectious processes such as meningitis, sepsis, or respiratory tract infections. Tumor necrosis factor alpha (TNF-alpha) and interleukin 1-beta (IL-1-beta) are important proinflammatory cytokines that are initially produced. These cytokines lead to the stimulation of complex humoral and cellular pathways and production of numerous secondary mediators such as other ILs, interferons, histamine, bradykinins, phospholipases, platelet-activating factor, arachidonic acid metabolites (i.e. leukotrienes and prostaglandins), complement components and other substances yet to be identified. 29, 39, 40 Numerous cytokines and inflammatory mediators (e.g. IL-1-beta, IL-2, IL-6, IL-8, TNF-alpha, histamine, leukotrienes and prostaglandins) have been detected in the MEF from experimental animals or from patients with OM. 41–49 Higher cytokine levels have been found in bacteria-positive samples than in bacteria-negative samples. 48, 49 Eradication of the bacteria was associated with reduction of concentrations of some cytokines, such as TNF-alpha, but not the others (i.e. IL-1) in the MEF samples collected 4 to 5 days into antibiotic treatment. The effects of viral infection on various cytokines and inflammatory mediators in the MEF of children with AOM have been studied at the University of Texas Medical Branch. Concentrations of histamine, tryptase, histamine-releasing chemokines, leukotrienes B4 (LTB4) and IL-8 in the MEF from children with AOM were determined and correlated with the presence or absence of bacteria and viruses, data are described below. Concentrations of histamine, a potent pharmacologic mediator of inflammation that causes vasodilatation and increases the permeability of middle ear mucosa, 50, 51 were determined in 677 MEF samples from 248 children with AOM. 52 Forty-seven percent of these children had documented concurrent viral infection. Histamine content was higher in bacteria-positive than in bacteria-negative MEF samples and higher in samples from patients with viral infection than in those from patients with no viral infection (Table 4). 52 Bacteria and viruses together had an additive effect on histamine content in the MEF. Antibiotic treatment for 3 to 5 days had no effect on reduction of histamine content in the MEF, and the pretreatment histamine content tended to be higher in patients with persistent OM than in those with good response to treatment. Table 4: Histamine concentrations in relation to presence of bacteria in the initial middle ear fluid sample in patients with acute otitis media with or without viral infection 52 *Tryptase content in the MEF and its correlation with histamine content was determined in a small study of MEF from 20 children with AOM. 53 Whereas histamine can be produced by both tissue mast cells and peripheral blood basophils, tryptase is specific to the mast cell origin. Tryptase concentrations were higher in the MEF containing bacteria and virus than in the MEF containing bacteria alone; MEF containing virus alone had the lowest concentrations of tryptase. However, because of small sample size, the differences were not significant statistically. There was no correlation detected between histamine and tryptase content in the MEF, suggesting that both mast cells and peripheral blood basophils may have produced histamine in the MEF. A study of 2 chemokines (macrophage-inflammatory protein 1-alpha and monocyte chemotactic protein 1), which are considered histamine-releasing factors, has also shown higher concentrations of these chemokines in the MEF containing both bacteria and virus than in the MEF containing bacteria alone. 54 LTB4 is a product of arachidonic acid metabolite, a potent inflammatory product of neutrophils, and relates directly to the acuteness of the middle ear disease and to the degree of inflammation. 55 IL-8 is a potent neutrophil-chemotactic cytokine. 56 LTB4 and IL-8 concentrations were measured in 271 MEF samples from 106 children with AOM, 42% of whom had evidence of concurrent viral infection. 11 The highest concentrations of LTB4 and IL-8 were found in the MEF containing both bacteria and virus (Table 5). 14 In 5 patients whose MEF samples were obtained from both right and left ears, the presence or absence of bacteria was identical in both ears. Levels of LTB4 and IL-8 were higher in the MEF that contained virus compared with the MEF without virus. High concentrations of LTB4 at the time of diagnosis and before antibiotic treatment were strongly correlated with an increased rate of treatment failure, and antibiotic treatment did not reduce the concentrations of these mediators. Table 5: LTB4 and IL-8 contents in initial middle ear fluid in relation to microorganism in specimen and concurrent viral infection 14Recovery from OM appears to be a very complex process. First it requires eradication of the pathogens by both nonimmunologic and immunologic mechanisms. Second it requires the return to normal Eustachian tube function and normal ventilation of the middle ear. 57 When Eustachian tube dysfunction continues and middle ear effusion persists, even after elimination of bacteria, immunologic activities and inflammatory cascades continue in the middle ear and can be self-perpetuated, leading to more prolonged disease and further tissue injury. The data presented here, taken together, suggest an active role of viruses in inducing the production of various cytokines and mediators which, in turn, may enhance the degree of inflammation or prolong the inflammation in the middle ear and Eustachian tube mucosa. Viruses may also affect neutrophil function causing delayed bacterial elimination from the middle ear, even when appropriate antibiotic is given. Finally the data suggest that antibiotic alone may not be adequate to arrest these complex inflammatory cascades. FUTURE DIRECTIONS Future research is needed to further elucidate the mechanisms of viral and bacterial interaction in OM recovery and to explore the strategies other than antibiotic treatment for AOM. Because of the significance of viruses in the pathogenesis and recovery of AOM, prevention of viral URI will lower the incidence of and improve the outcome of AOM. Although AOM can be induced by a wide variety of viruses and the realization of preventing disease by using vaccines against a variety of viruses may be a long way off, further about specific virus types and importance to OM will viral vaccines and other of the data the presence of viruses with adverse AOM outcomes are on methods for viral detection (i.e. viral viral antigen The that no pathogen or can be detected in of the MEF from patients with AOM suggests that these methods have viruses. a and for diagnosis of a wide of respiratory viruses has not been This has the of significance of various virus types molecular such as multiplex have been used in detection of a of viruses in MEF samples from AOM 58 These studies have shown that more respiratory viruses may be in AOM than previously If these can be for detection of a wide of viruses in clinical they will have potential to to further of the of OM. will be for such as the prevention of OM by using viral the treatment of URI or AOM with the reduction of antibiotic or the of as therapy of AOM. AOM, which is generally considered a bacterial is more likely a bacterial of viral however, can also induce signs and symptoms of AOM. The virus that causes URI enters the middle ear. When the middle ear is infected with both virus and bacteria or when viral URI is still ongoing at the time of bacterial AOM diagnosis, viral and bacterial interaction is of the middle ear is enhanced and and bacterial clearance from the middle ear is leading to adverse outcomes of the disease. Viruses affect recovery of AOM by a variety of some of which are not yet types of viruses may in to interact with bacteria. More methods for detection of a wide variety of viruses in a are needed to the relative significance of each virus This will vaccines or specific Further in the of the mechanisms of viral and bacterial interaction in AOM as well as in will be to the of new strategies for prevention or to this common disease. In the study of pharmacokinetics of amoxicillin in the MEF of was the amoxicillin highest in the MEF containing bacteria compared with MEF containing bacteria and virus or virus alone. The was but the data are consistent with the clinical findings that presence of virus in the middle ear with bacteriologic response to antibiotic treatment of AOM and support the that presence of virus has an adverse effect on antibiotic penetration into the middle ear. In the chinchilla model viral infections had no effect on the middle ear or however, bacteria increased either transport or the it is that in bacterial OM, more antibiotic the middle ear than in viral alone or viral bacterial infections. There is known about transport of antibiotics the epithelium of the and the however, is known about membrane transport in the middle ear. There is to about In viral infections be that the are the longer may the virus and the it is to the virus. the to the of the viral the infection is more In the studies presented did for the time after the of viral symptoms and for In the study of 271 children at all including and the duration of respiratory symptoms to OM. of symptoms did not a difference in Overall patients with persistent OM were significantly However, was significantly different only in the bacterial otitis without viral infection. The frequency of herpes virus infections in study was however, recent data suggest that herpes virus in the ear In studies but have tissue samples for As a in the and pathogenesis of OM, to culture viruses from Viruses be for at the the infection that is the MEF. is more to the MEF than it is to However, virus data from nasopharynx are also Presence of viruses in the nasopharynx is different from presence of bacteria but viruses detection of viruses in the active viral infection of the respiratory Some of these viruses enter the middle ear and some do was by of