BACTERIOLOGY OF ACUTE OTITIS MEDIA IN SPAIN: A PROSPECTIVE STUDY BASED ON TYMPANOCENTESIS

Abstract

Acute otitis media (AOM) is the most common bacterial infection in pediatric patients, therefore the evolution and spread of antibiotic resistance among ear pathogens has created justified concern. However, the etiology and antibiotic resistance patterns of the involved bacteria are unknown in many countries. The only reliable samples for such studies are those obtained by puncture of the tympanic membrane in the acute phase of otitis media. Aside from well-documented series mainly from the United States and Finland, the information remains scarce. Some English translations of papers published in Latin American countries illustrate to the English-speaking scientific community the etiology of the AOM in that area of the world.1 This paper presents the bacteriology of middle ear fluid collected prospectively from 104 AOM cases in Madrid. Patients and methods.Subjects and study design. Infants and children between 1 month and 14 years of age were enrolled for this study from June, 1989, to June, 1995. All children were previously healthy and were outpatients. Patients were excluded from the study if any of the following items were present: (1) previous history of otologic illness; (2) otorrhea; (3) craniofacial anomalies; (4) antibiotics taken in the preceding 7 days. Oral informed consent was obtained from parents or legal guardians. Diagnosis and definitions. We defined AOM by acute symptoms: earache (infant's irritability) and/or fever; and signs of middle ear effusions. The middle ear status was evaluated by pneumatic otoscopy (Welch Allyn Model 211). Tympanocentesis. Tympanocentesis was performed by one of the authors (FC) using a surgical head attached to a Riester® otoscope (Riester GmbH & Co.). Before tympanocentesis the external auditory canal was cleansed of cerumen with a blunt curet or by irrigating the ear canal. The canal was then filled with 70% ethyl alcohol for 1 to 2 min followed by a flush with saline solution. Tympanocentesis was performed with an Abbocath-T® 20-gauge needle (Abbott, Ltd.) attached to a tuberculin syringe. The syringe and the sheathprotected needle were promptly taken to the Department of Microbiology for immediate processing. Transport media were not used. Microbiology. All samples were cultured for aerobic/facultative, anaerobic bacteria and fungi. For aerobic/facultative bacteria plates of McConkey's agar, sheep blood Columbia agar and chocolate agar supplemented with Factors X and V were seeded. Incubation was at 35°C, in 10% CO2 atmosphere. For anaerobic organisms blood agar plates supplemented with hemin and vitamin K1, and phenylethyl alcohol blood agar plates were used; incubation was performed at 35°C under strict anaerobic conditions. For enrichment tubes of thioglycolate broth supplemented with hemin and vitamin K1 were used. The presence of fungi was investigated by seeding the samples in Sabouraud's agar (with and without chloramphenicol). All organisms recovered by culture were identified according to standard procedures.2 All samples were Gram-stained to evaluate the polymorphonuclear leukocyte content and the presence of typical bacterial or fungal morphotypes. Results. One hundred four children were enrolled in the study. Forty-six cases (44%) were in the infant age group; 31 cases (30%) were 1 to 3 years old and 27 cases (28%) were 4 to 11 years old. There were 55 female and 49 male patients. Symptoms. In 27 patients only the right ear was affected, in 21 patients only the left ear was affected and both ears were involved in 56 patients. The main symptoms in our patients were: earache/irritability 83%, fever 56% (only 5 cases exceeding 39°C), rhinitis/cough 51%, vomiting 26.5%, tiredness 18.6%. Septic clinical symptoms were not observed. Microbiology. Culture of middle ear effusion provided a total of 110 isolates (Table 1). In three-fourths (75.5%) of the 110 isolates a microbial pathogen was recovered by culture. In the other isolates (24.5%) the samples were either sterile or contained only saprophytic microorganisms from the external canal. Streptococcus pneumoniae was the most frequently isolated pathogen (36 cases, 32.7%), and in most of them (31 cases) as a single isolate. The second most common bacterial pathogen was Haemophilus influenzae (30 cases, 27.3%), again in most cases as a single infecting organism (26 cases). Therefore either S. pneumoniae or H. influenzae accounted for 79.5% of all bacteriologically documented and 59.6% of all the studied cases. Other isolated organisms were: Streptococcus pyogenes (5 cases, 4.5%); Escherichia coli (4 cases, 3.6%); Pseudomonas aeruginosa (3 cases, 2.7%); Staphylococcus aureus (2 cases, 1.8%); Bacteroides fragilis and Bacteroides gingivalis (one case each) and Moraxella catarrhalis (1 case, 0.9%). In 6 cases mixed cultures were obtained: S. pneumoniae and H. influenzae (4 cases); S. pneumoniae and E. coli (1 case); and E. coli and P. aeruginosa (1 case). Bilateral tympanocentesis was performed in 21 cases. In 16 of them the microbial organism recovered from both sites was identical: S. pneumoniae (7 cases); H. influenzae (3 cases); and 1 case each of S. pyogenes, Staphylococcus aureus and P. aeruginosa. In 3 cases culture was sterile in both sites. In 5 patients bacterial pathogens were recovered from only one site, the opposite being sterile: H. influenzae (2 cases), S. pneumoniae (1 case) and Bacteroides spp. (2 cases). Pathogen distribution according to age group. S. pneumoniae and H. influenzae were isolated in all age groups. S. pyogenes was obtained in 5 children ages 2 months (1 case), 2 years (2 cases), and 4 years (2 cases). Children with P. aeruginosa were aged 2 months, 3 months and 4 years. Eleven children were 3 months of age or less and the bacterial isolated were: S. pneumoniae (3 cases); E. coli (2 cases); and 1 case each of P. aeruginosa, S. pyogenes, Staphylococcus aureus, E. coli + P. aeruginosa, E. coli + S. pneumoniae and sterile. Antibiotic resistance among AOM pathogens. Fourteen (38.9%) of the 36 S. pneumoniae isolates had intermediate or high resistance to penicillin (MIC >0.125 μg/ml). High level penicillin resistance (MIC 2 μg/ml) was found in 6 cases (16.7%). Of the 30 H. influenzae strains 7 (23.3%) were beta-lactamase producers. Discussion. Acute otitis media is a clinical condition extensively studied and analyzed in a variety of papers published in the English literature. Nevertheless most of this work refers to US or Scandinavian series.3 In Europe, with the previously mentioned exception of Scandinavian countries, there is scant information about the etiologic agents of AOM. In a French series4, 5 the frequency of isolated pathogens was 25 to 37% S. pneumoniae, 25 to 40% H. influenzae, 1 to 5% M. catarrhalis and 1 to 8% S. pyogenes. The relative frequency of bacterial pathogens obtained in our study does not differ from that found in most international series of developed countries.6 As in our series, in most published studies about one-third of the cultured effusions were sterile.7 M. catarrhalis is scarcely represented in our series (a single isolate obtained in 1995). Before the 1980s M. catarrhalis was also considered as an infrequent AOM pathogen. Nevertheless during the last years, there has been a striking increase in M. catarrhalis isolates in the United States series,8 being currently higher than 10%.6 The same phenomenon has not been documented in some other countries. No isolate of M. catarrhalis was documented in a series of 105 infants with AOM studied in Israel during 1987 and 1988.9 Similarly, there was only 1% M. catarrhalis isolates in the Colombian series.1 In most French studies the rate of isolation of M. catarrhalis was only 1 to 3%, but these rates may be increasing for the latest years.4, 5 Very few data are available for the situation in Spain. The frequency of M. catarrhalis isolates among respiratory tract samples from children in Spain (1979 through 1987) was only 0.44%.10 In our series 39% of the S. pneumoniae isolates had intermediate (22.2%) or high level resistance (16.7%) to penicillin. The frequency of penicillin-resistant S. pneumoniae isolates in Spain is very high.11 In a national study involving 2,197 strains isolated from patients with systemic infections, the frequency of penicillin-resistant pneumococci rose from 6% in 1979 to 44% in 1989.12 A recent publication showed that the frequency of penicillin-resistant pneumococci in Madrid was 24% for strains with intermediate resistance and 22% for those with high resistance during 1992.13 The rate of beta-lactamase producers among our H. influenzae isolates was 23.3%. In a recent study in 10 Spanish towns an average rate of 35% beta-lactamase producers was found, the frequency being particularly high in the Madrid area (58.7%).14 In summary M. catarrhalis is an infrequent AOM pathogen in our series, 0.9%. The distribution frequency of AOM pathogens among Spanish children is similar to that found in the US at the beginning of the last decade. The rates of antibiotic resistance found in S. pneumoniae and H. influenzae AOM isolates reflect the general pattern of resistance previously described for these pathogens in Spain. Fernando del Castillo, M.D.; Adela Garcia-Perea, M.D.; Fernando Baquero-Artigao, M.D. Departments of Pediatrics (FC, FBA) and Microbiology (AGP) Hospital La Paz Universidad Autónoma de Madrid Madrid, Spain