Acute mastoiditis caused by Moraxella catarrhalis

1. Introduction 

Acute mastoiditis is the most frequent intratemporal complication of otitis media [1]. The bacterial etiology of acute mastoiditis varies, but Streptococcus pneumoniae (S. pneumoniae) is the most commonly found bacteria, representing 29–32% of cultures. Other commonly recovered pathogens in acute mastoiditis are Pseudomonas aeruginosa and Streptococcus pyogenes [1], [2], [3]. Haemophilus influenzae (H. influenzae) is found only rarely in the bacterial culture of acute mastoiditis [1], [4], [5].

The importance of Moraxella catarrhalis ( M. catarrhalis) as a pathogen in otitis media has increased during the last two decades [6], [7]. These gram-negative cocci, once considered harmless opportunists now form the third most common pathogen found in the cultures of middle ear-effusions (MEE), both in acute and secretory otitis media [6], [8], [9]. Today the incidence of M. catarrhalis in bacterial cultures taken in case of acute otitis media is almost equal in certain geographic areas with that of S. pneumoniae and H. influenzae [6]. Despite the fact that M. catarrhalis is an important middle ear pathogen, to our knowledge there are no reports of acute mastoiditis caused solely by it, although one report has indicated that when found together M. catarrhalis and S. pneumoniae have caused acute mastoiditis [10]. In this paper we describe a case of a 2-year-old girl with acute mastoiditis and M. catarrhalis in the bacterial culture of MEE.

2. Case report 

A previously healthy 2-year-old girl, without any past episode of acute otitis media, was admitted to a hospital because of suspected acute mastoiditis. Five days earlier she had developed symptoms of a common cold with rhinitis, cough and mild fever. Three days later her fever reached 40°C, and in addition to the respiratory symptoms, she vomited. Her physician had primarily diagnosed upper respiratory tract infection. The ear canal was clean and there was no otorrhea, but her left tympanic membrane was slightly reddish and cloudy, and its mobility was decreased. She was prescribed amoxicillin with the instructions to start the antibiotic treatment if the symptoms did not improve in a few days. However, the patient was not put on the medication. Two days later she still had a fever, there was a period of purulent discharge from her left ear, her left postauricular area was swollen, erythematous and tender and the pinna was protruded forward. At the second visit to her physician the left ear canal was cleaned. There was no signs of external otitis in the ear canal and the left tympanic membrane was bulging but otherwise intact. An otolaryngologist performed tympanocentesis, which revealed purulent discharge from the left tympanum and a bacterial culture was taken from the aspirate. The right tympanic membrane was also bulging, and there was purulent discharge in the right tympanum. Acute mastoiditis was diagnosed on the basis of the clinical picture of the disease, and the patient was sent to the Department of Otolaryngology, Helsinki University Central Hospital, for treatment and follow-up.

When admitted to the hospital, the patient was afebrile and alert, and there were no signs of meningeal irritation or facial paralysis. She weighed 10 kg. The auricular and periauricular status was as described earlier. Laboratory examination revealed a white blood cell count of 18 700/mm3, a hemoglobin level of 112 g/l and a c-reactive protein (CRP) level of 71. The patient was admitted to the children's ward, and cefuroxim (25 mg/kg) was given intravenously thrice daily. The patient's ears were cleaned twice a day with saline irrigation and suction, and chloramphenicol eardrops were used locally in the ears. Conventional radiographs taken of the mastoids the day after the patients admission to the hospital showed infective changes in the left tympanum and mastoid. Mastoid cells were small, undeveloped, totally opaque and filled with effusion. However, there were no radiological signs indicating that the bony trabeculae separating the mastoid cells had been destroyed. The child's clinical response to treatment was good. After 3 days of treatment, the discharge from the left ear ended, the clinical signs of acute mastoiditis disappeared, and CRP was 27 in the laboratory examinations. M. catarrhalis, which was resistant to penicillin and amoxicillin but susceptible to cephalosporins, was cultured from the MEE. The patient continued taking cefuroxime orally for 7 days, and she recovered uneventfully.

3. Discussion 

The bacteriology of otitis media has changed markedly over the last century, and this change has also contributed to the bacteriology of acute mastoiditis. In the beginning of the 20th century Streptococcus pyogenes was the most common bacteria in acute otitis media [11], but S. pneumoniae dominated during the last half of the century. During the last two decades the proportion of positive cultures of H. influenzae and M. catarrhalis in acute otitis media have markedly increased. S. pneumoniae and H. influenzae are known to cause acute mastoiditis, but this is the first report of acute mastoiditis caused solely by M. catarrhalis.

The use of antibiotics has decreased the number of complications of acute otitis media and the need for operative treatment of acute mastoiditis, but, at the same time, the clinical presentation of acute mastoiditis has somewhat changed [12], [13], [14]. Rapidly developing pain, tenderness, erythema and edema in the mastoid area following acute otitis media is still the most frequently seen clinical picture of acute mastoiditis. However, sometimes the clinical course of mastoiditis is much more obscure. Latent mastoiditis is usually preceded by a period of prolonged or recurrent otitis media treated with antibiotics [13]. Signs of otitis media can be found in most cases of latent mastoiditis, but the classical clinical picture of acute mastoiditis may be missing. On the other hand, latent mastoiditis can also appear without signs and symptoms of otitis media and an intratemporal or intracranial complication as the only presenting feature of the disease [14].

Our patient had not had otitis media episodes previously. In this case she primarily had symptoms of acute otitis media, and after 2 days she developed classical signs of acute mastoiditis. She took no antibiotic that could have interfered with bacterial culture. Therefore, the growth of M. catarrhalis alone in the culture of MEE makes it plausible to assume that this bacterium was the causative agent of acute mastoiditis in this case.

The pathogenic potential of M. catarrhalis is nowadays well established [15], although in otitis media it is still often considered clinically quite harmless bacteria. However, bacterial resistance to antibiotics is an increasing problem worldwide and today almost all strains of M. catarrhalis are β-lactamase producing [16], as in this case too. Furthermore, M. catarrhalis has been associated with an elevated risk of clinical failure to antibiotic treatment in acute otitis media [17]. Our patient was prescribed amoxicillin with instructions to start the treatment if the symptoms did not improve in a few days. The patient was not started on the medication, and in this particular case the prescribed antibiotic would probably not have cured her ear, but instead would have possibly prolonged the time before the correct diagnosis was made. This scenario indicates the importance of adequate patient follow-up by a physician and accurate diagnosis of acute otitis media and its complications. Today myringotomy and bacterial culture of MEE should always be done when there are signs of complications of acute otitis media or an unsatisfactory response to the treatment to identify the bacterial etiology of the infection.

The clinical significance of M. catarrhalis in acute otitis media has increased markedly over the past two decades [7], [18]. Now it seems that M. catarrhalis is also capable of provoking more serious consequences of acute otitis media and should be considered as an etiological factor of acute mastoiditis.